DOT/FAA/AR-04/11 

Office of Aviation Research 

Washington, D.C. 20591 

Fire-Safe Polymers and Polymer 

Composites 

September 2004 

Final Report 

This document is available to the U.S. public 

through the National Technical Information 

Service (NTIS), Springfield, Virginia 22161. 

U.S. Department of Transportation 

Federal Aviation Administration
NOTICE 

This document is disseminated under the sponsorship of the U.S. 

Department of Transportation in the interest of information exchange. The 

United States Government assumes no liability for the contents or use 

thereof. The United States Government does not endorse products or 

manufacturers. Trade or manufacturer's names appear herein solely 

because they are considered essential to the objective of this report. This 

document does not constitute FAA certification policy. Consult your local 

FAA aircraft certification office as to its use. 

This report is available at the Federal Aviation Administration William J. 

Hughes Technical Center’s Full-Text Technical Reports page: 

actlibrary.act.faa.gov in Adobe Acrobat portable document format (PDF). 
 Technical Report Documentation Page

1. Report No.

DOT/FAA/AR-04/11

2. Government Accession No. 3. Recipient's Catalog No.

 4. Title and Subtitle

FIRE-SAFE POLYMERS AND POLYMER COMPOSITES 

5. Report Date

September 2004

6. Performing Organization Code

7. Author(s)

Huiqing Zhang

8. Performing Organization Report No. 

9. Performing Organization Name and Address

Polymer Science and Engineering 

University of Massachusetts 

10. Work Unit No. (TRAIS)

Amhurst, MA 01003 11. Contract or Grant No.

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration

13. Type of Report and Period Covered

Office of Aviation Research

Washington, DC 20591

14. Sponsoring Agency Code

 ANM-110

15. Supplementary Notes

The FAA William J. Hughes Technical Center COTR was Dr. Richard Lyon. 

Copyright by Huiqing Zhang 2003 All Rights Reserved

16. Abstract 

The intrinsic relationships between polymer structure, composition, and fire behavior have been explored to develop new fire-safe

polymeric materials. 

Three milligram-scale methods (pyrolysis-combustion flow calorimetry (PCFC), simultaneous thermal analysis, and pyrolysis gas

chromatography/mass spectrometry (GC/MS)) have been combined to fully characterize the thermal decomposition and 

flammability of polymers and polymer composites. Thermal stability, mass loss rate, char yield, and properties of decomposition 

volatiles were found to be the most important parameters in determining polymer flammability. Most polymers decompose by

either an unzipping or a random chain scission mechanism with an endothermic decomposition of 100-900 J/g. Aromatic or 

heteroaromatic rings, conjugated double or triple bonds, and heteroatoms such as halogens, N, O, S, P, and Si, are the basic

structural units for fire-resistant polymers. The flammability of polymers can also be successfully estimated by combining the

pyrolysis GC/MS results or chemical structures with the thermogravimetric analysis. 

The thermal decomposition and flammability of two groups of inherently fire-resistant polymers—poly(hydroxyamide) (PHA)

and its derivatives and bisphenol C (BPC II) polyarylates—have been systematically studied. PHA and most of its derivatives

have extremely low heat release rates and very high char yields upon combustion. PHA and its halogen derivatives can

completely cyclize into quasi-polybenzoxazole structures at low temperatures. However, the methoxy and phosphate derivatives 

show a very different behavior during decomposition and combustion. Molecular modeling shows that the formation of an enol

intermediate is the rate-determining step in the thermal cyclization of PHA. BPC II-polyarylate is another extremely flameresistant polymer. It can be used as an efficient flame-retardant agent in copolymers and blends. From the PCFC results, the total

heat of combustion of these copolymers or blends changes linearly with composition, but the change of maximum heat release 

rates also depends on the chemical structure of the components. 

The flammability of various polymers and polymer composites measured by PCFC; cone calorimeter, ASTM E1354; and the

Ohio State University (OSU) calorimeter, ASTM E906, were also compared. For pure polymers, there was a relatively good 

correlation between different methods. However, for polymer composites with inert fillers or flame-retardant additives, the OSU 

and cone calorimetries are more suitable evaluation methods. 

17. Key Words 

Polymer, Fire, Flammability, Thermal analysis, Combustion

18. Distribution Statement 

This document is available to the public through the National 

Technical Information Service (NTIS), Springfield, Virginia 

22161.

19. Security Classif. (of this report)

 Unclassified 

20. Security Classif. (of this page)

 Unclassified

21. No. of Pages

 209

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY xix 

1. FIRE AND POLYMERS 1-1 

1.1 Introduction 1-1 

1.2 Polymer Combustion Process 1-2 

1.3 Standard Assessments and Tests 1-3 

1.4 Flame-Retardant Chemistry 1-4 

1.5 Inhibition of Polymer Combustion 1-5 

1.5.1 Intrinsically Fire-Resistant Polymers 1-5 

1.5.2 Flame-Retardant Additives 1-6 

1.6 Thermal Decomposition Mechanisms of Polymers 1-11 

1.7 Experimental Techniques for Thermal Decomposition of Polymers 1-12 

2. QUANTATIVE MEASUREMENTS ON THE THERMAL DECOMPOSITION

AND FLAMMABILITY OF POLYMERS 2-1 

2.1 Introduction 2-1 

2.2 Methodology of Flammability Calculations 2-2 

2.2.1 Calculation of the Composition of the Volatiles 2-3 

2.2.2 Calculation of Total Heat of Combustion and Heat Release Capacity 

of Polymers 2-4 

2.3 Experimental 2-5 

2.3.1 Pyrolysis GC/MS 2-5 

2.3.2 Simultaneous Thermal Analysis 2-5 

2.3.3 Pyrolysis-Combustion Flow Calorimeter 2-6 

2.3.4 Materials 2-7 

2.4 Results 2-8 

2.4.1 Thermal Stability and Decomposition Process of Polymers 2-8 

2.4.2 Thermal Decomposition Products of Polymers 2-13 

2.4.3 Flammability 2-16 

2.4.4 Bond Dissociation Energies of the Polymers 2-18 

iii
2.4.5 Flammability Calculated by Pyrolysis GC/MS and STA Results 2-21 

2.4.6 Flammability Estimated by Using Chemical Structure and TGA 

Results 2-22

2.5 Discussion 2-28 

3. LOW FLAMMABILITY AND THERMAL DECOMPOSITION OF POLY

(HYDROXYAMIDE) AND ITS DERIVATIVES 3-1 

3.1 Introduction 3-1 

3.2 Experimental 3-2 

3.2.1 Materials 3-2 

3.2.2 Film Preparation 3-3 

3.2.3 Characterization 3-3 

3.3 Results 3-3 

3.3.1 Thermal Stability and Decomposition Process of PHAs 3-3 

3.3.2 Flammability 3-10 

3.3.3 Characterization of Chars by IR and Elemental Analysis 3-13 

3.3.4 Identification of Volatiles by GC/MS 3-15 

3.3.5 Thermal Decomposition Mechanisms 3-19 

3.4 Discussion 3-23 

4. FIRE-RESISTANT, UV/VISIBLE-SENSITIVE POLYARYLATES,

COPOLYMERS, AND BLENDS 4-1 

4.1 Introduction 4-1 

4.2 Experimental 4-2 

4.2.1 Materials 4-2 

4.2.2 Characterization 4-2 

4.3 Results 4-2 

4.3.1 Flammability and Thermal Decomposition of BPA-Polyarylates 4-2 

4.3.2 Thermal Decomposition and Flammability of Homopolyarylates 4-3 

4.3.3 UV/Visible-Sensitive Chalcon II-Polyarylate 4-6 

4.3.4 Thermal Decomposition and Flammability of Copolymers and 

Terpolymers 4-8

iv
4.3.5 Thermal Decomposition and Flammability of Blends 4-12 

4.4 Discussion 4-15 

5. EFFECTS OF FLAME-RETARDANT ADDITIVES AND CORRELATIONS

AMONG PCFC, OSU, AND CONE CALORIMETERS 5-1 

5.1 Introduction 5-1 

5.2 Experimental 5-2 

5.2.1 Test Samples 5-2 

5.2.2 Sample Preparation 5-2 

5.2.3 Characterization 5-2 

5.3 Results 5-5 

5.3.1 Poly(Methyl Methacrylate)/Clay Nanocomposites 5-5 

5.3.2 Poly(Ether Ether Ketone) and Composites 5-7 

5.3.3 Xydar and Its Composites 5-12 

5.3.4 Polyphthalamides and Composites 5-17 

5.3.5 Epoxy Resins With Phosphate Flame Retardants 5-28 

5.3.6 Ignitability 5-32 

5.3.7 Heat Release Rate 5-33 

5.3.8 Correlation Between Different Flammability Tests 5-35 

5.4 Discussion 5-39 

6. STRUCTURE-COMPOSITION-FLAMMABILITY RELATIONSHIPS OF

POLYMERS 6-1

6.1 Introduction 6-1 

6.2 Experimental 6-1 

6.2.1 Materials 6-1 

6.2.2 Characterization 6-1 

6.3 Chemical Structure 6-1 

6.3.1 Main Chain—Polysulfones 6-1 

6.3.2 Semiorganic Network Structure—Polycarbynes and Polysilynes 6-11 

6.3.3 Substituents 6-14 

6.3.4 Flame-Retardant Comonomers 6-20 

6.4 Composition—Copolymers and Blends 6-26 

6.4.1 Poly(Methyl Methacrylate)/Polystyrene Random Copolymers 6-26 

6.4.2 Poly(Methyl Methacrylate)/Polystyrene Blends 6-26 

v
6.5 Molecular Weight 6-28 

6.5.1 Poly(Methyl Methacrylate) 6-28 

6.5.2 Polystyrene 6-30 

6.5.3 Poly(Ethylene Oxide) 6-32 

6.5.4 Mechanisms of the Effects of the Molecular Weight 6-32 

6.6 Free-Radical Scavenger—TEMPO 6-33 

6.6.1 Polystyrene or PMMA/TEMPO Blends 6-34 

6.6.2 The PMMA/PS Random Copolymers Initiated by TEMPO 6-34 

6.7 Discussion 6-38 

7. MOLECULAR MODELING OF THERMAL CYCLIZATION OF

POLY(HYDROXYAMIDE) 7-1

7.1 Introduction 7-1 

7.2 Previous Experimental Results 7-1 

7.3 Results 7-3 

7.4 Discussion 7-7 

8. CONCLUSIONS AND RECOMMENDATIONS 8-1 

8.1 Conclusions 8-1 

8.1.1 Characterization of Thermal Decomposition and Flammability of 

Polymers 8-1

8.1.2 Inherently Fire-Resistant Polymers 8-2 

8.1.3 Effects of Flame-Retardant Additives and Correlations Among 

Different Flammability Tests 8-4 

8.1.4 Structure, Composition, and Flammability Relationships 8-5 

8.1.5 Thermal Cyclization Mechanism of PHA 8-6 

8.2 Recommendations 8-6 

9 REFERENCES 9-1 

10. BIBLIOGRAPHY 10-1 

APPENDIX A—SUPPLEMENTARY DATA

vi
LIST OF FIGURES

Figure Page 

1-1 Schematic Diagram of Polymer Burning 1-2 

1-2 Intrinsically Fire-Resistant Polymers 1-6 

1-3 Intumescent Compounds 1-9 

1-4 Some Preceramic Polymers 1-10 

2-1 Schematic Picture of PCFC 2-6 

2-2 Chemical Structures of Some Polymers 2-7 

2-3 The STA and DTG Curves of Aliphatic Polymers (10°C/min in N2) (a) HDPE, (b) 

PS, (c) PMMA, and (d) PVC 2-10 

2-4 The STA and DTG Curves of Aromatic Polymers (10°C/min in N2) (a) PC and 

(b) PPhS 2-11 

2-5 The STA and DTG Curves of Polymers With Exothermic Decomposition 

(10°C/min in N2) (a) PAN and (b) BPC II-Polyarylate 2-11 

2-6 Activation Energies of Thermal Decomposition Calculated by TGA Data (a) 

HDPE, (b) Nylon 66, and (c) PPhS 2-12 

2-7 Pyrolysis GC/MS Traces of Additional Polymers (4.3°C/s to 930°C) (a) PMMA, 

(b) PE, and (c) PS 2-14 

2-8 Pyrolysis GC/MS Traces of Aromatic Polymers (4.3°C/s to 930°C) (a) PC and 

(b) PPhS 2-15 

2-9 Pyrolysis GC/MS Traces of Polymers at a Fast Heating Rate (10°C/ms to 930°C) 

(a) HDPE and (b) PC 2-16 

2-10 The TGA Curves of Kevlar and Nylon 66 2-21 

2-11 Calculation of Gross Heat of Combustion of Small Organic Compounds 

(a) Oxygen Consumption and (b) Atom Additivity 2-24 

2-12 Comparison of Calculated Net Heat of Combustion of Polymers With PCFC 

Results (a) Oxygen Consumption and (b) Element Additivity 2-25 

2-13 Comparison of Calculated Heat Release Capacity of Polymers With PCFC 

Results (a) Oxygen Consumption and (b) Element Additivity 2-27 

vii
2-14 Correlation Between Char Yield and Molar Fraction of Effective Char-Forming 

Atoms in Polymers 2-28 

3-1 Structures of PHA and Its Derivatives 3-2 

3-2 The TGA Curves of PHA-1 and 2 in N2 3-5

3-3 X-Ray Diffraction of PHA-1 and 2 3-5 

3-4 The TGA Curves of PHA-1 and Its Derivatives in N2 (a) PHA-1 and Halogenated 

PHAs, (b) PHAs With Methoxy Groups, and (c) PHAs With Phosphinate or 

Phosphate Groups 3-6 

3-5 Effects of Oxygen on the Decomposition of PHA-1 and Its Derivatives (a) PHA-1 

and Its Methoxy Derivative, (b) Halogenated PHAs, and (c) Phosphate PHAs, 

(1) in N2 and (2) in Air 3-8 

3-6 High-Temperature DSC Curves of PHA-1 and Its Derivatives (a) PHA-1 and 

Halogenated PHAs, (b) PHAs With Methoxy groups, and (c) PHAs With 

Phosphinate or Phosphate Groups 3-9 

3-7 Derivative TGA Curves of PHA-1 and Its Derivatives (a) PHA-1 and 

Halogenated PHAs, (b) PHAs With Methoxy Groups, and (c) PHAs With 

Phosphinate or Phosphate Groups 3-12 

3-8 Infrared Spectra of PHA-1 at Different Temperatures 3-14 

3-9 Pyrolysis GC/MS Traces of PHA-1 and Its Derivatives (Heating to 930°C at 

4.3°C/s) (a) PHA-1, (b) PHA-3, (c) PHA-5, (d) PHA-7, (e) PHA-10, and 

(f) PHA-12 3-16 

3-10 Pyrolysis GC/MS Traces of PHA-1 at Different Temperature Ranges 

(Heating Rate, 4.3°C/s) (a) 250° ~ 383°C and (b) 383° ~ 930°C 3-17 

3-11 Pyrolysis GC/MS Traces of PHA-7 at Different Temperature Ranges 

(Heating Rate, 4.3°C/s) (a) 350° ~ 469°C and (b) 469° ~ 930°C 3-18 

3-12 Pyrolysis GC/MS Traces of PHA-10 at Different Temperature Ranges 

(Heating Rate, 4.3°C/s) (a) 250° ~ 500°C and (b) 500° ~ 930°C 3-19 

3-13 Presumed Cyclization of PHA and Its Derivatives 3-20 

3-14 Water Generated by Intermolecular Reaction 3-20 

3-15 Proposed Thermal Decomposition Mechanisms of PHAs 3-21 

4-1 Structures of BPA-, Chalcon II-, and BPC II-Polyarylates 4-2 

viii
4-2 The TGA and DTG Curves of BPA-, Chalcon II-, and BPC II-Polyarylates 4-3 

4-3 High-Temperature DSC Curves of BPA-, Chalcon II-, and BPC II-Polyarylates 4-4 

4-4 Pyrolysis GC/MS Traces of BPA-, Chalcon II-, and BPC II-Polyarylates

(Temperature Range: 250° ~ 930°C, Heating Rate: 4.3°C/s) (a) BPA-Polyarylate, 

(b) Chalcon II-Polyarylate, and (c) BPC II-Polyarylate 4-5 

4-5 Ultraviolet Spectra of Polyarylates Containing Chalcon II-Monomer 

(a) Homopolymers and (b) BPA-Chalcon II Copolymers 4-6 

4-6 Photo-Cross-Linking of Chalcon II-Polyarylate 4-7 

4-7 Thermal Decomposition of Chalcon II-Polyarylate After UV/Visible-Exposure 

(a) Full TGA Curves and (b) Initial Decomposition 4-7 

4-8 Thermal Decomposition of Chalcon II-BPC II Copolymers (The Numbers Are 

Molar Ratios) (a) TGA and (b) DSC 4-8 

4-9 Thermal Decomposition of BPA-Chalcon II-BPC II Terpolymers (The Numbers 

Are Molar Ratios) (a) TGA and (b) DSC 4-9 

4-10 Ternary Plot of Flammability of Copolymers and Terpolymers 4-10 

4-11 Composition and Flammability Relationship of Copolymers (a) Heat Release 

Capacity, (b) Total Heat Released, (1) BPA-Chalcon II, (2) BPA-BPC II, and 

(3) Chalcon II-BPC II 4-11 

4-12 The TGA Curves of PSF (BPA-)/BPC II-Polyarylate Blends (a) PSF/BPC IIPolyarylate and (b) BPA-/BPC II-Polyarylate 4-12 

4-13 The TGA Curves of PS (PEO)/BPC II-Polyarylate Blends (a) PS/BPC IIPolyarylate and (b) PEO/BPC II-Polyarylate 4-13 

4-14 Structure-Composition-Flammability of Blends Containing BPC II-Polyarylate 

(a) Heat Release Capacity, (b) Total Heat Released, and (c) Char Yield, (1) PS, 

(2) PEO, (3) BPA-polyarylate, and (4) PSF 4-14 

5-1 Thermal Decomposition of PMMA/Clay Nanocomposites 5-6 

5-2 Thermal Decomposition of PEEK and Its Composites in N2 5-7

5-3 Thermal Decomposition of PEEK and Its Composites in Air 5-8 

5-4 High-Temperature DSC Curves of PEEKs 5-8 

5-5 Pyrolysis GC/MS Traces of PEEK (a) 300°-930°C, 4.3°C/s; (b) 300°-930°C, 

10°C/ms; and (c) 585°-590°C, 10°C/min 5-10

ix
5-6 Cone HRR Curves of PEEK and Its Composites 5-11 

5-7 Thermal Decomposition of Xydar and Its Composites in N2 5-12

5-8 High-Temperature DSC Curves of Xydar and Its Composites 5-13 

5-9 Thermal Decomposition of Xydar Materials in Air 5-14 

5-10 Pyrolysis GC/MS Traces of Xydar (4.3°C/s to 930°C) 5-15

5-11 Ohio State University HRR Curves of Xydar Composites by Thermopile 5-15 

5-12 Cone HRR Curves of Xydar Composites 5-17 

5-13 Thermal Decomposition of PPA Materials (a) A-1000 Series and 

(b) A-6000 Series 5-18 

5-14 High-Temperature DSC Curves of PPA Materials 5-19 

5-15 Pyrolysis GC/MS Traces of PPA Materials (Pyrolysis Condition: 300°~930°C at 

a Heating Rate of 4.3°C/s for (a) A-1000; (b) A-6000; (c) AF-1133 V-0; 

(d) AFA-6133 V-0, 10°C/min for (e) AF-1133 V-0, 400°~405°C; and 

(f) AFA-6133 V-0, 405°~410°C) 5-20

5-16 Ohio State University HRR Curves of A-1000 Series 5-23 

5-17 Ohio State University HRR Curves of A-6000 Series 5-25 

5-18 Cone HRR Curves of A-1000 Series 5-25 

5-19 Cone HRR Curves of A-6000 Series 5-26 

5-20 Composition of Phosphate-Retarded Epoxy Resin 5-28 

5-21 Thermal Decomposition of Epoxy/Phosphate Composites (a) DMMP, 20°C/min; 

(b) TMP, 40°C/min; and (c) TPP, 40°C/min 5-29

5-22 Pyrolysis GC/MS Traces of Epoxy/DMMP Composites (Heat Rate, 4.3°C/s) 

(a) 150°~300°C and (b) 300°~930°C 5-30

5-23 Cone HRR Curves of Expoxy/TMP Composites 5-32 

5-24 Ignition Time of Polymers Under Different External Heat Fluxes 5-33 

5-25 Peak Heat Release Rate of Polymers Under Different External Heat Fluxes 5-34 

5-26 Correlations of PHRR Between Different Flammability Tests 5-37 

x
5-27 Correlations of Total Heat Released Between Different Flammability Tests 5-38 

6-1 Chemical Structures of Polysulfones 6-2 

6-2 Thermogravimetric Analysis and DTG Curves of Polysulfones in N2 6-2 

6-3 The TGA and DTG Curves of Polysulfones in Air 6-3 

6-4 High-Temperature DSC Curves of Polysulfones 6-3 

6-5 The TGA and DTG Curves of Polysulfones at Different Heating Rates (a) PSU, 

(b) PES, and (c) PPhS 6-5 

6-6 Kissinger Plot of Polysulfones Decomposed in N2 6-6

6-7 Pyrolysis GC/MS Traces of Polysulfones (a) PSU, (b) PES, and (c) PPhS 6-7 

6-8 The OSU HRR Curves of Polysulfones Measured by Thermopile 6-9 

6-9 Cone HRR Curves of Polysulfones 6-11 

6-10 Schematic Structures of Polycarbynes and Polysilynes 6-12 

6-11 The TGA and DTG Curves of Polycarbynes 6-12 

6-12 The TGA and DTG Curves of Polysilynes 6-13 

6-13 Chemical Structures of Polymethacrylates 6-14 

6-14 The TGA and DTG Curves of Polymethacrylates 6-15 

6-15 Thermal Decomposition Products of Polymethacrylates (a) Ethyl Methacrylate, 

(b) Isobutyl Methacrylate, and (c) Benzyl Methacrylate 6-16 

6-16 Chemical Structures of Cyano-Substituted Polymers 6-17 

6-17 The TGA and DTG Curves of Cyano-Substituted Polyamides 6-17 

6-18 The TGA and DTG Curves of PA-CN(X) and Poly(Azomethine) Compared 

With Technora and Kevlar 6-18

6-19 High-Temperature DSC Curves of CN-Substituted Polymers 6-18 

6-20 Pyrolysis GC/MS Traces of PA-CN (X) and Poly(Azomethine) (a) Technora, 

(b) PA-CN (25), (c) PA-CN (50), and (d) Poly(Azomethine) 6-19 

6-21 Copolymerization of Polyethylene With POSS-Norbornene 6-21 

6-22 The TGA and DTG Curves of the PE/POSS Copolymer 6-21 

xi
6-23 Flammability-Composition Relationship of PE/POSS Copolymers 6-22 

6-24 Synthesis of Cross-Linked Epoxy Vinyl Ester Resins Based on BPC I and II 6-23 

6-25 The TGA and DSC Curves of BPC II-Based Epoxy Vinyl Ester Resins (B Series) 

(a) TGA and (b) DSC 6-24 

6-26 Pyrolysis GC/MS Traces of BPC I-Based Epoxy Vinyl Ester Resin A1 

(a) 170°~330°C and (b) 170°~930°C 6-25

6-27 The TGA Curves of PMMA/PS Copolymers by Radical Polymerization 6-26 

6-28 Flammability-Composition Relationship of PMMA/PS Random Copolymers 6-27 

6-29 Thermal Decomposition Processes of PMMA/PS Blends 6-27 

6-30 Flammability-Composition Relationship of PMMA/PS Blends 6-28 

6-31 The TGA and DTG Curves of PMMAs With Different Molecular Weights 

(a) TGA and (b) DTG 6-29 

6-32 The PCFC Curves of PMMAs With Different Molecular Weights 6-30 

6-33 Thermal Decomposition of PS With Different Molecular Weights 6-31 

6-34 Thermal Decomposition of PEO With Different Molecular Weight 6-32 

6-35 Thermal Decomposition of PMMAs With Low Molecular Weight 6-33 

6-36 The TGA and DTG Curves of PS/TEMPO Blends 6-34 

6-37 The TGA and DTG Curves of PMMA/TEMPO Blends 6-35 

6-38 TEMPO-Initiated PMMA/PS Copolymers 6-35 

6-39 The TGA and DTG Curves of TEMPO-Initiated PMMA/PS Copolymers 6-36 

6-40 Flammability-Composition Relationship of PMMA/PS Copolymers Initiated by 

TEMPO 6-36

6-41 Pyrolysis GC/MS Traces of PMMA/PS Copolymers (a) Random Copolymer and 

(b) TEMPO Initiated 6-37 

6-42 Effects of TEMPO on Polymer Decomposition 6-37 

7-1 Thermal Decomposition Processes of PHA and Its Derivatives 7-2 

7-2 Possible Thermal Cyclization Mechanism of PHA and Its Derivatives 7-2 

xii
7-3 Bond Dissociation Energies of PHA, Its Methoxy and Phosphate Derivatives 

(unit in kJ/mol) 7-3 

7-4 Molecular Structures of the Model Compound 7-4 

7-5 Proposed Cyclization Mechanism of PHA 7-4 

7-6 Keto-Enol Rearrangement by a Direct Hydrogen Shift 7-4 

7-7 Keto-Enol Rearrangement by a Six-Member Ring Transition State 7-5 

7-8 Enol-Structure Transformations by Rotation and Bending 7-6 

7-9 Cyclization Into PBO Through ENL2 Intermediate 7-6 

7-10 Cyclization Into PBO Through ENL4 Intermediate 7-7 

xiii
LIST OF TABLES 

Tables Page 

2-1 Cross-Section Regression Coefficients 2-3 

2-2 Thermal Decomposition Properties of Polymers 2-9 

2-3 Flammability of Different Polymers (930°C at 4.3°C/s) 2-17

2-4 Bond Dissociation Energies of Polymers 2-19 

2-5 Bond Dissociation Energies in Aliphatic-Aromatic Polymers 2-20 

2-6 Correlation Between Different Methods 2-22 

3-1 Thermal Decomposition of PHA and Its Derivatives in N2 3-4

3-2 Flammability of PHA and Its Derivatives 3-11 

3-3 Elemental Analyses of PHA-1 and Its Chars at Different Temperatures 3-13 

3-4 Infrared Band Assignments of PHA and PBO 3-14 

4-1 Flammability and Thermal Decomposition of BPA-Polyarylates 4-3 

4-2 Flammability and Thermal Decomposition of Homopolyarylates 4-4 

4-3 Flammability and Thermal Decomposition of Co- and Terpolymers 4-10 

5-1 Sample Compositions 5-3 

5-2 Flammability and Thermal Decomposition of PMMA/Clay Nanocomposites 5-6 

5-3 Gel Permeation Chromatograhy GPC Results of PMMAs 5-7 

5-4 Thermal Decomposition Properties of PEEKs 5-9 

5-5 Flammability of PEEKs Measured by PCFC 5-11 

5-6 Flammability of PEEKs Measured by the Cone Calorimeter 5-11 

5-7 Thermal Decomposition Properties of Xydar Materials in N2 5-13

5-8 Thermal Decomposition Properties of Xydar Materials in Air 5-14 

5-9 Flammability of Xydar and Its Composites by PCFC 5-14 

5-10 Ohio State University Results of Xydar Composites 5-16 

xiv
5-11 Cone Calorimeter Results of Xydar Composites 5-17 

5-12 Thermal Decomposition and Flammability of PPA Materials 5-22 

5-13 Flammability of A-1000 Series Measured by the OSU Calorimeter 5-23 

5-14 Flammability of A-6000 Series Measured by the OSU Calorimeter 5-24 

5-15 Cone Calorimeter Results of PPA Materials 5-27 

5-16 Thermal Decomposition and Flammability of Epoxy/Phosphate Composites 5-31 

5-17 Cone Calorimeter Results of Expoxy/TMP Composites 5-31 

5-18 Critical Heat Flux and Thermal Property Calculated From the Cone Calorimeter 5-33 

5-19 Material Flammability Obtained by Cone Calorimeter Data 5-35 

5-20 Flammability Measured by PCFC, OSU, and Cone Calorimeters 5-36 

6-1 Thermal Decomposition Properties of Polysulfones 6-4 

6-2 Bond Dissociation Energies and Activation Energies of Polysulfones 6-6 

6-3 Flammability of Polysulfones Measured by PCFC 6-8 

6-4 Flammability of Polysulfones Measured by the OSU Calorimeter 6-8 

6-5 Flammability of Polysulfones Measured by the Cone Calorimeter 6-10 

6-6 Flammability and Thermal Decomposition of Polycarbynes and Polysilynes 6-14 

6-7 Flammability and Thermal Decomposition of Polymethacrylates 6-15 

6-8 Flammability and Thermal Decomposition of PA-CN(X) Polyamides 6-20 

6-9 Thermal Decomposition Products of PE/POSS Copolymers 6-21 

6-10 Flammability and Thermal Decomposition of PE/POSS Copolymers 6-22 

6-11 Composition of BPC-Based Epoxy Vinyl Ester Resins (wt%) 6-23 

6-12 Thermal Decomposition and Flammability of BPC-Based Epoxy Vinyl Ester 

Resins 6-25

6-13 Flammability and Thermal Decomposition of PMMA/PS Copolymers 6-27 

6-14 Flammability and Thermal Decomposition of PMMA/PS Blends 6-28 

6-15 Flammability and Thermal Decomposition of PMMAs 6-30 

xv
6-16 Flammability and Thermal Decomposition of PS 6-31 

6-17 Flammability and Thermal Decomposition of PEOs 6-32 

6-18 Flammability of PS/TEMPO Blends 6-34 

6-19 Flammability of PMMA/TEMPO Blends 6-35 

6-20 Flammability and Thermal Decomposition of PMMA/PS Copolymers Initiated by 

TEMPO 6-36

xvi
LIST OF ACRONYMS

BPA Bisphenol A 

BPC II Bisphenol C

CO Carbon monoxide 

Cov Coefficient of variation 

CTMA Br Cetyltrimethylammonium 

CUMIRP Center for University of Massachusetts/Industry Research on Polymers 

DMAc N,N-dimethylacetamide 

DMMP Dimethoxy methyl phosphate 

DMSO Dimethyl sulfoxide 

DSC Differential scanning calorimetry 

DTG Derivative of thermogravimetric 

EHC Effective heat of combustion 

FAA Federal Aviation Administration 

FH Fluorohectorite 

FTIR Fourier Transform Infrared Spectroscopy 

GC Gas chromatography 

H/C Hydrogen to carbon ratio 

HCl Hydrogen chloride 

HDPE High-density polyethylene 

HF Hartree-Fock 

HRR Heat release rate 

HRRav Mean value from tig to 180 sec. after 

IR Infrared spectroscopy 

LOI Limiting oxygen index 

MMT Montmorillonite 

Mp Molecular weights 

MS Mass spectrometry 

N2 Nitrogen 

NBS National Bureau of Standards 

NIST National Institute of Standards and Technology

NMP N-methylpyrrolidinone 

OSU Ohio State University 

P(α-M-S) Poly(α-methyl styrene) 

PAN Poly(acrylonitrile) 

PBI Polybenzimidazole 

PBO Polybenzoxazole 

PBT Poly(butylene terephthalate) 

PBZT Polybenzthiazoles 

PC Polycarbonate 

PCFC Pyrolysis-combustion flow calorimeter 

PDMS Polydimethylsiloxane 

PE Polyethylene 

PEEK Poly(ether ether ketone) 

PEO Poly(ethylene oxide) 

PES Poly(ether sulfone) 

xvii
PET Poly(ethylene terephthalate) 

PHA Poly(hydroxyamide) 

PHRR Peak heat release rate 

PI Polyimide 

PMMA Poly(methyl methacrylate) 

POB Polybenzoxazole 

POM Poly(oxymethylene) 

POSS Polyhedral Oligomeric Sisesquioxanes 

PP Polypropylene 

PPA Polyphthamide (Amodel) 

PPhS Poly(phenyl sulfone) 

PPO Poly(phenylene oxide) 

PS Polystyrene 

PSF Polysulfone 

PSU BPA-polysulfone 

PTFE Poly(tetrafluoroethylene 

PVC Poly(vinyl chloride) 

S Styrene 

SEA Smoke extinction area 

STA Simultaneous thermal analysis 

TGA Thermogravimetric analysis 

THF Tetrahydrofuran 

THR Total heat released 

TIC Total ionization current 

TMP Trimethyl phosphate 

TPP Triphenyl phosphate 

UV Ultraviolet 

xviii
EXECUTIVE SUMMARY

The intrinsic relationships between polymer structure, composition, and fire behavior have been 

explored to develop new fire-safe polymeric materials. 

Different experimental techniques, i.e., three milligram-scale methods (pyrolysis-combustion 

flow calorimetry (PCFC), simultaneous thermal analysis, and pyrolysis gas chromatography/

mass spectrometry (GC/MS)), have been combined to fully characterize the thermal 

decomposition and flammability of polymers and polymer composites. Thermal stability, mass

loss rate, char yield, and properties of decomposition volatiles were found to be the most

important parameters in determining polymer flammability. Most polymers decompose by either

an unzipping or a random chain scission mechanism with an endothermic decomposition of 100-

900 J/g. Aromatic or heteroaromatic rings, conjugated double or triple bonds, and heteroatoms

such as halogens, N, O, S, P, and Si, are the basic structural units for fire-resistant polymers. 

The flammability of polymers can also be successfully estimated by combining the pyrolysis 

GC/MS results or chemical structures with the thermogravimetric analysis. 

The thermal decomposition and flammability of two groups of inherently fire-resistant

polymers—poly(hydroxyamide) (PHA) and its derivatives and bisphenol C (BPC II)

polyarylates—have been systematically studied. PHA and most of its derivatives have extremely 

low heat release rates and very high char yields upon combustion. PHA and its halogen 

derivatives can completely cyclize into quasi-polybenzoxazole structures at low temperatures.

However, the methoxy and phosphate derivatives show a very different behavior during 

decomposition and combustion. Molecular modeling shows that the formation of an enol 

intermediate is the rate-determining step in the thermal cyclization of PHA. BPC II-polyarylate

is another extremely flame-resistant polymer. It can be used as an efficient flame-retardant agent 

in copolymers and blends. From the PCFC results, the total heat of combustion of these 

copolymers or blends changes linearly with composition, but the change of maximum heat 

release rates also depends on the chemical structure of the components. 

The flammability of various polymers and polymer composites measured by PCFC; cone 

calorimeter, ASTM E1354; and the Ohio State University (OSU) calorimeter, ASTM E906, were

also compared. For pure polymers, there was a relatively good correlation between different 

methods. However, for polymer composites with inert fillers or flame-retardant additives, the 

OSU and cone calorimetries are more suitable evaluation methods. 

xix/xx
1. FIRE AND POLYMERS.

1.1 INTRODUCTION. 

Polymers are widely used in many applications. However, most polymers, like the majority of

other organic compounds, will burn readily in air or oxygen. The flammability of polymers is a

serious issue and severely limits their applications [1 and 2]. Recent fire safety concerns put 

even more stringent requirements for the materials used in enclosed and inescapable areas, such

as electronic enclosures, high-rise buildings, submarines, ships, and aircraft cabins [3]. Lightweight, high-performance polymeric materials offer many advantages in these applications over 

conventional metal and ceramic materials, but they greatly increase the fire risk because of their 

flammability and possible release of toxic by-products. 

According to some studies, about 20% of those who die in airplane crashes are killed by fire, 

most often because several tons of polymers used in seat fabrics, overhead bins, and wall and

windows will burn, leaving passengers limited time to escape [4]. In order to improve aircraft 

safety, the Federal Aviation Administration (FAA) initiated a long range Fire Research Program 

in 1995. The long-term objective is “to eliminate burning aircraft cabin materials as a cause of 

death,” which will require an order-of-magnitude reduction in cabin fire hazards relative to

current cabin materials [5]. For this reason, sponsored by the FAA, National Institute of 

Standards and Technology (NIST), the U.S. Army, and industry, the Center for University of 

Massachusetts/Industry Research on Polymers (CUMIRP) established a new research cluster, 

Fire-Safe Polymers and Polymer Composites, which involved synthesis, characterization, 

modeling, and processing. The goal of this cluster was not only to develop new fire-safe 

materials to be used in future commercial aircraft, but also to understand the thermal 

decomposition and fire-resistance mechanisms on a molecular level to reduce unwanted fires and

extend polymer applications. 

The research conducted in this report was part of the CUMIRP Cluster F program and was

focused on the following fundamental studies: 

• Developing and using new experimental techniques to characterize the thermal 

decomposition and flammability of polymers; 

• Establishing the correlation between polymer structure, composition, and their 

macroscopic flammability; 

• Understanding the effects of various flame-retardant additives on the polymer

flammability; 

• Deducing polymer thermal decomposition and fire-resistance mechanisms. 

Different experimental techniques, i.e., pyrolysis gas chromatography/mass spectrometry 

(GC/MS), simultaneous thermal analysis (STA), and pyrolysis-combustion flow calorimetry

(PCFC), were combined to measure the flammability and thermal decomposition of different 

polymeric materials. All three methods required only a very small amount of sample (about a

milligram or less), so they are especially suitable for research materials that are only available in

1-1
limited quantities. As a result, these methods are efficient screening tools for newly synthesized 

fire-safe materials. By discovering the intrinsic relationships between polymer structures, 

composition, and their fire behavior, the research goal is to help identify and design new fire-safe 

polymeric materials. 

1.2 POLYMER COMBUSTION PROCESS.

Many polymers, if subjected to some suitable ignition sources, will undergo self-sustained 

combustion in air or oxygen [6]. In general, nonpolymeric materials (e.g., matches, cigarettes, 

torches, or electric arcs) are the main sources of ignition, but polymers are most frequently 

responsible for the propagation of a fire. A burning polymer constitutes a highly complex 

combustion system. Chemical reactions may take place in three interdependent regions: within 

the condensed phase, at the interface between the condensed phase and gas phase, and in the gas 

phase. 

Polymer combustion occurs as a cycle of coupled events [7]: (1) heating of the polymer, (2)

decomposition, (3) ignition, and (4) combustion. The polymer is first heated to a temperature at 

which it starts to decompose and gives out gaseous products that are usually combustible. These 

products then diffuse into the flame zone above the burning polymer. If there is an ignition 

source, they will undergo combustion in the gas phase and liberate more heat. Under steadystate burning conditions, some of the heat is transferred back to the polymer surface, producing

more volatile polymer fragments to sustain the combustion cycle. This process is shown in 

figure 1-1. 

FIGURE 1-1. SCHEMATIC DIAGRAM OF POLYMER BURNING [8] 

There are two types of combustion involved when polymers are burned: flaming combustion 

and nonflaming combustion [9]. 

Flames are self-propagating combustion reactions in which both the fuel and the oxidant are 

present in the gas phase. Since most polymers are hydrocarbon based, the flame above burning 

polymers is usually a hydrocarbon flame. The principal reactions in the flames are free-radical 

reactions. The most important radicals in hydrocarbon flames are simple species such as H⋅, O⋅, 

and OH⋅, and a small amount of HO2⋅, HCO⋅, and CH3⋅. Chain-branching reactions in the 

1-2
combustion process, for example H⋅ + O2 → HO⋅ + O⋅, can accelerate the burning of polymers 

by generating more radicals. Smoke formation in flames is highly dependent on the structure of

the gaseous fuel and on the fuel-to-oxidant ratio. Normally, polymers containing purely aliphatic 

structural units produce relatively little smoke, while polymers with aromatic groups in the main 

chain produce intermediate amounts of smoke. 

Nonflaming combustion, including smouldering and glowing combustion, propagates through 

the polymer by a thermal front or wave, involving the surface oxidation of the pyrolysis products 

[7]. Glowing combustion differs from smouldering combustion in that it is accompanied by pale

flames of carbon burning to form carbon monoxide. Smouldering combustion usually occurs 

with polymeric materials of high-surface area that can form a residual carbonaceous char. It is 

generally accompanied by the generation of smoke due to pyrolysis at or near the surface. 

Glowing combustion occurs after the initial charring of the material. 

From a practical point of view, it is also important to consider the associated fire hazards. The 

effects resulting from polymer combustion, which can threaten human life, include oxygen 

depletion, flame, heat, smoke, hot and toxic combustion gases, and structural failure. The two 

major causes of fire-related deaths are inhalation of toxic gases and burns [10 and 11]. 

1.3 STANDARD ASSESSMENTS AND TESTS.

To fully evaluate the fire behavior of different polymers, it is necessary to develop standard tests 

for assessing the flammability and other combustion-related properties of polymers. Most 

countries have standards and codes for the classification of materials with respect to their 

combustion behavior, but the experimental setup used in existing standard tests varies 

considerably, according to the nature, shape, and size of the polymeric materials to be tested.

The fire tests most commonly used in the USA are the UL 94 small-flame test [12], the ASTM 

E 84 Steiner Tunnel [13], and the ASTM E 622 National Bureau of Standards (NBS) smoke 

chamber [14]. However, these tests can be used only as guides and suffer from problems with 

precision and reproducibility. 

The majority of fire tests used now are concerned with the determination of the following fire 

properties of materials [10]. 

• 

• 

• 

• 

• 

• 

Ease of ignition—how readily a material ignites 

Flame spread—how rapidly fire spreads across a surface 

Fire endurance—how rapidly fire penetrates a wall or barrier 

Rate of heat release—how much heat is released and how quickly 

Ease of extinction—how rapidly or how easily the flame chemistry leads to extinction 

Smoke evolution—amount, evolution rate, and composition of smoke released during

stages of a fire 

1-3
• Toxic gas evolution—amount, evolution rate, and composition of gases released during 

stages of a fire 

Among them, the oxygen concentration test is a very important ignition test, from which the

limiting oxygen index (LOI) [15] can be obtained. The LOI is defined as the minimum oxygen 

concentration at ambient temperature needed in an inert gaseous medium for the material to 

achieve sustained burning after ignition. The precision and reproducibility of the results are two 

reasons for the wide acceptance of this method. 

According to the research done at NIST [16], the heat release rate (HRR) is the most important 

variable in a fire. Therefore, it is easy to assess the fire hazard of a product by measuring the 

HRR in a realistic large-scale test or predicting it from small-scale engineering tests. The heat

release calorimeters are available in three scales: room-scale, single full-article scale, and smallscale, also known as bench-scale. The small-scale cone calorimeter is the one used by most

polymer and flame retardant additive manufacturers [17]. For air transportation, the FAA has a 

number of flammability requirements [18]. The most important is the test for cabin wall 

materials using the Ohio State University (OSU) HRR apparatus. The criteria used by the FAA 

are very strenuous, and only advanced composites especially designed for aircraft use are 

normally able to pass the requirements. 

1.4 FLAME-RETARDANT CHEMISTRY.

When a polymer breaks down in thermal decomposition, the following types of products may be

formed [7]: (1) combustible gases, e.g., methane, ethane, and carbon monoxide; (2) 

noncombustible gases, e.g., carbon dioxide, hydrogen chloride, and hydrogen bromide; (3) 

liquids, which are often partially degraded polymers; (4) finely divided solid particles consisting 

of decomposing polymer fragments or soot in the combustion gases; and (5) discrete solids in the 

form of a carbonaceous residue or char. The evolution of large volumes of highly flammable 

gases will clearly tend to increase the flammability of polymers. Liquid products are not as 

readily combustible as gaseous products, but liquids can spread heat to adjacent parts of the 

polymer structure. Therefore, reducing the amount and speed of generation of combustible gases 

and preventing flame spreading are the most basic methodologies to achieve flame retardancy. 

Generally, there are two mechanisms by which polymer combustion can be inhibited [10]. One

is solid-phase inhibition, involving changes in the polymer substrates. Low-density, highporosity chars tend to be the most desirable decomposition products from the nonflammability

point of view. The chars can have the useful functions including helping to preserve structural 

integrity, insulating the underlying polymer from the heat of the flame, and preventing 

production of new fuel and further burning. However, a char sometimes undergoes smouldering 

combustion, leading to the formation of large amounts of smoke. This effect usually happens 

only at very high temperatures. Another very important factor in the polymer combustion cycle 

is the net heat of combustion of the gaseous products, which is the heat released by the combined 

combustion reactions minus the heat needed to bring the polymer from its initial state to the

combustion stage. Therefore, if a system can evolve water and some other noncombustible gases 

or have large endothermic demands for thermal decomposition, the flammability can be reduced. 

1-4
The other flame-retardant mechanism is vapor-phase inhibition, involving changes in the flame

chemistry. In these systems, reactive species such as bromine and chlorine are built into the 

polymer and are transformed into volatile free-radical inhibitors during burning, such as

hydrogen chloride (HCl). These materials diffuse into the flame and inhibit the radical reactions 

by changing highly reactive species H⋅ and HO⋅ into less reactive Br⋅ and Cl⋅. Two examples of 

the radical scavenge reactions are H⋅ + HCl → H2 + Cl⋅ and HO⋅ + HCl → H2O + Cl⋅. As a

result, the combustion cycle is interrupted. 

For many materials, both solid and vapor-phase inhibition are involved. It is difficult in practice 

to distinguish among the different mechanisms by which the flaming combustion of an organic 

polymer is being inhibited. 

1.5 INHIBITION OF POLYMER COMBUSTION.

The most efficient way to prevent polymer combustion is to design inherently fire-resistant 

polymers that have high thermal stability, resistance to the spread of flame, and low burning rate 

even under high heat flux [19]. However, these materials are generally not easy to process and 

are very expensive. Another strategy is to use flame-retardant additives to inhibit the

combustion of polymers, especially for the commodity polymers. The details about these two 

choices are discussed below. 

1.5.1 Intrinsically Fire-Resistant Polymers.

Most polymers with high thermal stability are intrinsically fire resistant. Due to their high

decomposition temperature, the initial breakdown will be effectively prevented and the

combustion process will not be initiated. This high-temperature property of polymers can be 

improved by increasing the interactions between polymer chains or by chain stiffening [20].

Chain interactions can be enhanced by several means, such as increasing crystallinity, the

introduction of polar groups, and hydrogen bonding. Chain stiffening can be accomplished by

the use of aromatic or heterocyclic structures in the polymer backbone, such as in poly(pphenylene), aromatic polyamides, and polyesters. In addition, polymers containing considerable 

numbers of aromatic groups in the structural units have great tendencies to condense into chars 

on heating. They, therefore, produce less flammable gaseous products in a flame. In all, 

polymers that have high thermal stability and generate less flammable volatiles on

decomposition are the most desired fire-resistant polymers. 

There are three general types of structures for the intrinsically fire-resistant polymers: linear 

single-strand polymers consisting of a sequence of cyclic aromatic or heterocyclic structures,

ladder polymers, and inorganic or semiorganic polymers [20]. So far, most carbon-based, fireresistant polymers are prepared by incorporating highly stable, rigid, aromatic, or heterocyclic

ring systems directly into the polymer chain [21-23], such as polyimide (PI), polybenzoxazole 

(PBO), polybenzimidazole (PBI), and polybenzthiazoles (PBZT) (see figure 1-2). The synthetic

routes to such polyaromatic heterocyclic polymers involve a two-step process in which soluble

high-molecular-weight prepolymers are first synthesized, and then rigid stable rings are formed

by thermally or chemically induced condensation of reactive groups on the polymer chains. 

1-5
S

S N

N n

O

N N

O n

N

H

N N

N

H

n

C

N

C C

N

C

O

O

O

O

n

PBI PBZT 

PI PBO

FIGURE 1-2. INTRINSICALLY FIRE-RESISTANT POLYMERS 

Ladder polymers are a very special type of rigid-chain polymers [24 and 25]. These polymers

are double-stranded structures consisting of two polymer chains periodically bound together by 

chemical bonds such as cyclized polyacrylonitrile ( ). In principle, these materials 

should show superior thermal stability because the polymer chains cannot be severed by 

breaking a single bond. 

N N n

The synthesis of inorganic and semiorganic polymers has been aimed at the production of stable,

polymeric materials having linear chains consisting of such typical repeating units as siliconnitrogen, boron-nitrogen, and phosphorus-nitrogen [26 and 27]. The nonburning characteristics 

of inorganic elements and the formation of nonflammable protective coatings are the two main 

reasons for the fire resistance of these polymers. 

1.5.2 Flame-Retardant Additives.

From the manufacturing point of view, the introduction of flame-retardant additives undoubtedly

constitutes the easiest way of making a polymer less flammable. There are two types of 

additives: reactive and additive flame retardants [28]. The reactive flame retardants are the 

compounds containing heteroatoms known to confer some degree of flame retardance, and they 

are built chemically into the polymer molecule. Alternatively, the additive flame retardant can

be physically mixed with existing polymers. In this case, the compounds do not react chemically 

with the polymers. The flame retardants most abundantly used at the present time are based 

largely on six elements: boron, aluminum, phosphorus, antimony, chlorine, and bromine. In 

addition, nitrogen and silicon can also confer some degree of flame retardance. Other elements 

and their compounds have proved to be less effective. Combinations of flame retardants often 

have synergistic or antagonistic effects. Sometimes a heteroatom already present in the polymer

backbone may interact with a flame retardant and, thus, exhibit synergism or antagonism. 

Although additive flame retardants are widely used in polymers, there are some limitations such

as poor compatibility, high volatility, deleterious effects on the properties of polymers, and 

increase of the production of carbon monoxide (CO) and smoke [29]. 

Flame-retardant additives can act by a variety of mechanisms in either the condensed phase or 

the gas phase [28]. They can terminate the free-radical reactions in the condensed phase, act as 

heat sinks due to their heat capacity, form a nonflammable protective coating or char to insulate 

the flammable polymer from the source of the heat and oxidant, and interrupt the flame 

1-6
combustion in the gas phase. It is difficult, however, to unequivocally attribute a single mode of 

action to a particular additive or class of additives. Many flame retardants appear to be capable

of functioning simultaneously by several different mechanisms, often depending on the nature of 

the organic polymers. 

1.5.2.1 Inorganic Hydroxide Flame Retardants.

Inorganic hydroxides are a very important class of flame retardants due to their relatively low

cost, ease of handling, and low toxicity [30]. Aluminium oxide trihydrate is used in the largest 

quantities by far as an inorganic flame retardant for polymers [31]. It is normally introduced into

polymers in large quantities (>50% by weight) in order to attain a significant flame-retardant 

effect. This addition reduces the amount of combustible materials available for decomposition.

During decomposition, this filler compound acts as a heat sink and, thus, delays the polymer 

from reaching its decomposition temperature [32]. When heated, it decomposes to form

anhydrous alumina and releases water, which is an endothermic reaction. This energy

consumption can remove the heat from the substrate, slow the decomposition of the substrate, 

and keep it below its ignition temperature. Also, water released into the vapor phase dilutes the

concentration of the combustible gases. The oxide residue generated during decomposition has a

relatively high heat capacity, which can reduce the heat transfer to the substrates. Another

advantage of using inorganic hydroxides is that they can reduce the amount of smoke generated 

on combustion [33]. 

Due to its low thermal stability, aluminum oxide trihydrate should be used below 200°C. Other

inorganic hydroxides and hydroxycarbonates [34] also have some flame-retardant action. For 

example, magnesium hydroxide is more thermally stable and can be used above 300°C. 

1.5.2.2 Halogenated Flame Retardants.

Halogen-containing flame retardants make up one of the largest groups of additives in the plastic 

industry. As reactive flame retardants, halogen-containing alkenes, cycloalkanes, and styrene 

can be copolymerized directly with the corresponding nonhalogenated monomers [35]. As

additive flame retardants, these organic-halogenated compounds are most commonly used in 

conjunction with phosphorus compounds or with metal oxides, especially antimony oxide. The 

stability of the halogen compounds goes as F>Cl>Br>I. Iodine compounds are not sufficiently 

stable to be used commercially, whereas the fluorine compounds are too stable to be generally 

useful. Bromine and chlorine compounds are the most generally used halogen-containing flame

retardants. Bromine compounds are more effective than chlorine compounds on a weight basis, 

but they are considerably more expensive. 

Halogen-containing flame retardants may function either in the vapor phase or in the condensed 

phase [29 and 35]. The action of the flame retardant depends on the structure of the additive and 

of the polymer. Generally, the radicals produced by thermal decomposition of a halogenated 

flame retardant can interact with the polymer to form hydrogen halide. Hydrogen halides inhibit 

the radical propagation reactions that take place in the flame by reacting with the most active 

radicals, H⋅ and OH⋅. It also should be noted that aromatic-brominated compounds can produce 

large amounts of char. 

1-7
Although halogen compounds are quite widely used on their own in flame retardants, their 

effectiveness is sometimes considerably increased by a free-radical initiator and antimony 

trioxide. Antimony-halogen systems can affect the combustion of polymers by their ability to 

act both in the gas and the condensed phases [7]. 

Although there is an increasing legislation against the use of halogenated compounds in 

disposable items that must be recycled or land filled, brominated and chlorinated flame 

retardants still occupy the largest share of the flame-retardant market. 

1.5.2.3 Phosphorus-Based Flame Retardants.

Both inorganic and organic phosphorus compounds are useful for imparting flame retardance to 

many polymers. Phosphorus flame retardants include elemental red phosphorus, water-soluble 

inorganic phosphates, insoluble ammonium polyphosphate, organophosphates and phosphonates, 

phosphine oxides, and chloroaliphatic and bromoaromatic phosphates [36]. 

Both additive and reactive flame retardants are commercially available. Additive compounds, 

especially phosphates, are widely used for highly hydroxylated polymers such as cellulose. The 

most extensively employed reactive flame retardants are phosphorus-containing polyols used in 

polyurethane foams [37]. Other reactive flame retardants include vinyl and allyl phosphonates 

[38]. 

The flame-retardance mechanisms of these phosphorus compounds include the formation of a

surface glass to protect the substrate from oxygen and flame, promoting of charring, and freeradical inhibition generally proposed for halogens [35]. The flame-retardant mechanism for 

phosphorus depends on the type of phosphorus compound and the chemical structure of the 

polymer. Phosphorus flame retardants containing halogens or nitrogen are often stated to exhibit 

synergistic behavior due to the formation of phosphorus halides or oxyhalides or P-N bonds on 

decomposition [39 and 40]. 

Recently, there is an increased interest in intumescent systems, which can develop a foamed char 

on the surface of the polymeric materials during burning. The combination of ammonium 

polyphosphate, dipentaerythritol, and melamine is the most commonly used intumescent flameretardant system [41]. Generally, intumescence requires a carbonific (char former) such as a 

polyol, a catalyst or acid source such as a phosphate, and a spumific (gas generator) such as a

nitrogen source. The mechanism involves decomposition of the phosphate to phosphoric acid, 

esterification of the polyol, and, subsequently, decomposition and regeneration of the phosphoric 

acid. Ammonium polyphosphate with a high ammonia content helps blow the forming char to a 

porous product. This surface char insulates the substrate from flame, heat, and oxygen. There 

are also some self-intumescing compounds that contain all three required functions in a single 

molecule (figure 1-3). Such intumescent coatings can satisfy environmental and toxicity issues 

because the coatings are halogen-free and the decomposition gases are water and ammonia. 

1-8
HO OH

HO OH

H3PO4

O

O

O

O P

O

O P O

O

CH2O

O

P

O

HOCH2 O

CH2O

O

P

O

P O

O

CH2O OCH2

O

OCH2

O

P

O

O

Carbonific

Catalyst

Acid source

melamine

spumific

+ +

melamine melamine

Chargard 329 (Great Lakes Chemical)

CN-1197 (Great Lakes Chemical)

melamine

FIGURE 1-3. INTUMESCENT COMPOUNDS [41] 

1.5.2.4 Nitrogen-Based Flame Retardants.

The presence of nitrogen in natural polymers appears to exert some degree of flame retardance, 

as shown by the relatively low flammability of wool, silk, and leather [42]. Synthetic polymers 

that contain nitrogen are not so resistant to combustion. A number of nitrogen-containing

organic compounds are used as reactive flame retardants for certain polymers. These include 

triazines, isocyanates, urea, guanidine, and cyanuric acid derivatives [43]. Some of these 

compounds are also employed as additive flame retardants, often in conjunction with phosphorus

compounds, to reduce the flammability of cellulosic textiles. In the latter cases, the nitrogen 

appears to act to a considerable extent by strengthening the attachment of phosphorus to the

polymer, but nothing is yet certain about the mechanisms of action. One possible explanation is 

that the release of nitrogen or ammonia dilutes the volatile polymer decomposition products and, 

hence, makes them less flammable. Ammonium salts and metal-amine complexes have also

been quite widely used as flame retardants for certain applications, such as ammonium 

phosphates for wood. 

1.5.2.5 Silicon-Containing Flame Retardants.

There is a renewed interest in using silicon-based flame retardants as substitutes for the halogens

or phosphorus [44]. Almost all forms of silicon have been explored: silicones, silicas,

organosilanes, silsesquioxanes, and silicates. The most common flame retardant based on silicon 

is in the form of polyorganosiloxane, in particular, polydimethylsiloxane (PDMS). The 

flammabilities of the block copolymers of various types of polycarbonate (PC) and poly(ether 

imide) with PDMS [45] show significant decreases. Silicon can also be incorporated into the

1-9
branches of the polymer chains [46]. Under certain cases, the addition of silica can also affect 

the flammability properties of materials [47]. The formation of a silicon-based protective surface 

layer appears to be the flame-retardant mechanism for silicone and silica systems. 

Polycarbosilane, polysilastyrene, and polysilsesquioxane preceramic polymers, shown in 

figure 1-4, are also used to blend with various thermoplastics, [48 and 49]. 

Si

CH3

H

PCS

n

Polycarbosilane

Si

Ph

CH3

PSS

n

Polysilastyrene

FIGURE 1-4. SOME PRECERAMIC POLYMERS 

Studies [48 and 49] show that they are all effective flame retardants. They can reduce the peak

HRR and average HRR, but the total heat released remains unchanged. The primary reason for 

the lower HRR for the blends is the reduced mass loss rate, i.e., the rate at which fuel is released

into the gas phase is slowed by the presence of the ceramic char. 

Recently, there is a great interest in the flammability properties of polymer-clay (layered-silicate) 

nanocomposites [50 and 51]. Cone calorimetry data show that both the peak and average heat 

release rate are reduced significantly for intercalated and delaminated nanocomposites with low

silicate mass fraction (3%-5%), but there is little improvement in the char yield. Polymer-clay

nanocomposites are materials that may fulfill the requirements for a high-performance, additivetype flame-retardant system. 

In general, a condensed-phase mechanism, which involves a protective surface layer, is proposed

for silicon-based flame retardants. 

1-10
1.5.2.6 Boron-Based Flame Retardants.

Borate treatments were the first to be extensively applied to cotton and then to wool. Boric acid

and borax are frequently used together [52]. On evaporation of the water of hydration, the 

polymers swell and an intumescent coating is formed on the surface, which insulates the bulk of 

the polymer from the heat source. The enhancement of the char formation, the endothermic 

dehydration process and the dilution of the gaseous breakdown products by the water released 

could be the reasons for the flame retardance of boron-containing additives. Cyclic borate esters

have been used as durable additives for cellulose, and boric acid and polyols have been 

incorporated into rigid polyurethane foams [7]. 

1.5.2.7 Polymeric Flame Retardants.

Polymeric flame retardants have been much less studied than their small molecule counterparts 

even though they have many advantages. By the incorporation of a polymeric flame retardant, 

the physical and mechanical properties of the polymer are less affected. It can also avoid the 

outward diffusion in the system and consequent risk of environmental contamination. 

Polydibromostyrene and polyphosphazenes are among some of these flame retardants [53 and 

54]. In a broad sense, all the fire-resistant polymers can be used as polymeric flame retardants to

be blended with some other polymers to enhance fire retardancy. As a matter of fact, this is a

very convenient way to adjust polymer flammability by composition. 

1.6 THERMAL DECOMPOSITION MECHANISMS OF POLYMERS.

The thermal decomposition of polymers involves interacting chemical and physical processes [7 

and 10]. The chemical processes are responsible for the generation of flammable volatiles and 

physical changes, such as melting and charring, can alter the decomposition and burning 

characteristics of a material. In most cases, a solid polymer, when heated to a certain 

temperature, will decompose to give varying amounts of volatile products and solid residues.

These residues can be carbonaceous (char), inorganic (originating from heteroatoms contained in 

the original polymer, either within the structure or as a result of additive incorporation), or a 

combination of both. Many fire tests have shown that char formation is an important route to

achieve flame retardancy, but little is understood about the detailed structure of char or how it 

forms. Van Krevelen [55] has proposed a two-step model for charring. Below 550°C, the 

polymers decompose to fuel gases, tars, and a primary char. On further heating above 550°C, the 

primary char is slowly converted to a conglomerate of loosely linked small graphitic regions, 

which is virtually independent of the structure of original polymers. Levchik and Wilkie [56] 

also proposed that the char formation of polymers includes the following steps: cross-linking, 

aromatization, fusion of aromatics, turbostratic char formation (an incomplete process of 

graphitization), and graphitization. The formation of char can be promoted through many 

chemical reactions, including graft copolymerization, Lewis acid catalysis, Friedel-Crafts

chemistry, redox reactions, and the use of various additives. As to the structure of char, it is

believed that char is composed of polynuclear aromatic compounds with heteroatoms (O, N, 

P, S), consisting of crystalline and amorphous regions. 

1-11
The thermal decomposition processes for different polymers are varied and complex. The rate, 

mechanism, and product composition of these thermal decomposition processes depend on both 

the physical properties and chemical composition of the original material. In the thermal

decomposition of organic polymers, four general mechanisms can be identified [7]: (1) randomchain scission (polyethylene), (2) end-chain scission (unzipping) (poly(methyl methacrylate)),

(3) chain stripping (poly(vinyl chloride)), and (4) cross-linking (high-charring polymers). Some

polymers undergo a reaction that exclusively belongs to one category. Others exhibit mixed 

behavior, depending on the structures of polymers. Many of the addition polymers, such as vinyl 

polymers, seem to decompose through a reverse polymerization (initiation, propagation, chain 

transfer, and termination) or random chain scission. Polymers prepared by a condensation 

process, such as polyesters and polyamides, decompose according to random chain scission 

followed by cross-linking into carbonaceous chars. However, the detailed decomposition 

mechanisms of different polymers are greatly dependent on their chemical structure and 

composition. 

1.7 EXPERIMENTAL TECHNIQUES FOR THERMAL DECOMPOSITION OF

POLYMERS.

To discover new fire-resistant polymers and to help understand how and why polymers burn 

using structure-property correlations, small-scale experimental techniques suitable for research

materials need to be developed. Thermogravimetric analysis (TGA) is an important method to

study the thermal reactions of polymers in the condensed phase [57]. By far, most experimental 

work has been carried out in an inert gas atmosphere. Few studies have been made of the

influence of oxygen on the thermal decomposition of polymers. It was suggested that oxygen 

from the surrounding atmosphere is usually completely consumed in the flame zone so that the 

pyrolysis of the condensed-phase polymer takes place in the absence of oxygen [7]. However, 

some experimental results suggest that oxygen is also involved in the thermal decomposition of 

some polymers, but the extent of its involvement varies considerably with the nature of the

polymer and the experimental conditions under which it burns [58]. 

TGA data can provide information about the thermal stability of various polymeric materials, the

rate and amount of volatile products to which they give rise under a range of well-controlled 

conditions, and the amount of the corresponding solid residue. Experiments involve both 

isothermal weight-loss measurements and nonisothermal techniques. The isothermal technique 

requires almost instantaneous heating of the polymer sample to the desired temperature. The 

nonisothermal technique involves a programmed linear increase of sample temperature as a 

function of time. It is also very convenient for getting the mass loss rate versus time from the 

derivative of the thermogravimetric (DTG) data by differentiating the TGA curve. DTG is a

good procedure to identify the temperature range at which the various stages of thermal

decomposition take place and the order in which they occur. In addition to the rate of 

decomposition, the heat involved in the decomposition process is also of interest. Common

differential scanning calorimetry (DSC) cannot be used for thermal decomposition process due to 

its low applicable temperature (below 600°C). Simultaneous STA with TGA and DSC 

performed at the same time to a high temperature of 1200°C is very useful in measuring the heat 

evolved or absorbed during decomposition. 

1-12
In addition to the kinetics and thermodynamics of the thermal decomposition process, there are 

also concerns with the nature of the decomposition process. Pyrolysis GC/MS is a simple but 

rapid and extremely sensitive method to characterize the volatiles produced during polymer 

decomposition [59]. It is also capable of measuring the relative composition of the volatiles so 

that the heat of combustion of pyrolysis gases can be estimated. By identifying the 

decomposition products at different temperatures and different heating rates, the decomposition 

mechanism can be elucidated. There are also some other methods that can be used to 

characterize volatiles, such as infrared spectroscopy (IR) and thermal volatilization analysis [60]. 

Chars are complex materials that are usually insoluble. This limits their characterization to the 

tools used in solid-state chemistry and physics. The chemical structure of the char is usually 

characterized by elemental analysis. Other properties are characterized through microscopy, 

various spectroscopies, X-ray diffraction, and thermal conductivity [61]. 

In all, it is not easy to evaluate the fire behavior of polymers because the thermal decomposition 

processes of polymers are varied and complex, and the fire performance of polymers is also 

dependent on the test methods and experimental conditions used. There are still unsolved issues 

regarding the fire-retardant mechanisms. Therefore, a combination of techniques is essential to 

the understanding of the complex issue of fire-retardant polymers. 

1-13/1-14
2. QUANTATIVE MEASUREMENTS ON THE THERMAL DECOMPOSITION AND

FLAMMABILITY OF POLYMERS.

2.1 INTRODUCTION. 

How to evaluate the fire performance of polymers accurately is a very important issue. There are

already some standard tests for assessing the flammability of polymers, such as the oxygen 

concentration test [15], Underwriter Laboratories Test for Flammability of Plastic Materials 

(UL 94) [12], the ASTM E 84 Steiner Tunnel [13], the NBS smoke chamber tests [14], the cone 

calorimeter test [62], and the OSU calorimeter test [63]. 

However, all the standard tests available now require relatively large samples (at least tens of

grams), and the results are highly dependent on the sample configuration and combustion 

conditions. Thus, it was recognized that it would be a great improvement if a new, small-scale, 

convenient, and quantitative test could be developed to measure flammability of materials. 

PCFC, which was designed by the FAA, is such a flammability test [64-66]. It is operated on the 

oxygen consumption principle, i.e., the net heat of complete combustion of typical organic 

molecules per mole of oxygen consumed is relatively constant, C = 419 ±19 kJ/mol-O2 = 13.1 

±0.6 kJ/g-O2, and independent of the chemical composition of the combusted materials. Using 

only milligram samples, it is an extremely good method to characterize materials that are only

available in a small amount. The samples are pyrolyzed in an inert gas stream followed by hightemperature, nonflame combustion of the volatiles in excess oxygen. The heat release rate, total 

heat of combustion of the volatiles as well as the char yield can be directly obtained from PCFC. 

Heat release capacity (J/g-K), which is defined by dividing the heat release rate by the linear 

heating rate and sample weight, is a material flammability parameter that, in theory, depends 

only on the chemical composition of the solid. Therefore, it should be a reliable measure of the 

fire hazard of a material [64-66]. 

The correlations between PCFC and some standard tests, such as oxygen bomb calorimeter

according to ASTM D 2382, cone calorimeter at 50 kW/m2

 incident heat flux according to

ASTM E 1354 and UL 94, are all fairly good [67]. A transition from burning (HB) to selfextinguishing (V-0) behavior in the UL 94 test occurs over a relatively narrow range of heat 

release capacities, 300-400 J/g-K. In the PCFC method, pyrolysis is limited to small samples, so 

there is no temperature gradient and mass transfer limitation. Hence, the intrinsic material 

flammability can be evaluated. However, because the sample temperature is uniform during 

pyrolysis and combustion and the heat produced in combustion cannot be delivered back to 

pyrolysis process, the PCFC results do not exactly reflect the transient aspects of the fire 

behavior associated with sample thickness, temperature gradient, char buildup, heat feedback and 

some other physical processes in a real fire. In addition, complete combustion of the fuel gases

in the high-temperature furnace is an equilibrium process and will not reflect the gas-phase, 

flame-retardant effect of some additives, which is kinetically based. 

In this section, this new milligram-scale combustion calorimeter PCFC has been used to 

quantitatively measure polymer flammability. With the aid of two other experimental 

techniques, pyrolysis GC/MS (Py-GC/MS) and STA, the correlations between polymer structure, 

composition, and their thermal decomposition/flammability have been explored. By analyzing

the decomposition products at different pyrolysis conditions using pyrolysis GC/MS and 

2-1
measuring the corresponding decomposition process using STA, the heat release rates and total 

heats of combustion of polymers were calculated. By parametric fits of some mechanistic

models to TGA data, the kinetic parameters, such as the activation energy of thermal 

decomposition, were determined. The bond dissociation energies of some polymers have also

been calculated by using a quantum computational method, B3LYP density-functional method 

with a standard polarized split-valence 6-31G (d) basis set. The relationship of bond dissociation

energies and activation energies of thermal decomposition was examined. Furthermore, the heat 

release rates, total heat released, and char yields of different polymers were estimated by using a 

simple calculation method based on the known chemical structure of polymers and TGA results. 

2.2 METHODOLOGY OF FLAMMABILITY CALCULATIONS.

The three methods described above—pyrolysis GC/MS, STA and PCFC—are all essential in 

determining the fire properties of polymers. They are complementary to each other. By relating 

the results from one method to another, the whole decomposition and combustion process of 

polymers can be elucidated, and the validation of each method can also be achieved. 

It was found that the heat released (Qc) during transient heating of a material to or above its 

oxygen-free thermal decomposition temperature in time, t, is [64-66] 

[h x m x dx

dx

d Q t v

o

c v

t

c ( ) ( ) ( ) , ∫0 = − ] 2-1

where is the enthalpy of complete combustion per unit mass of volatile pyrolysis products 

and is the amount of volatiles generated. 

o hc,v

mv

The peak heat release rate per unit mass is [64-66] 

T Tp o

o

c ,v

o

max

max c

c dt

dm(T )

m

h (T )

m

Q h

=

= = & & 2-2

where 

( ) , p

o hc v T is the net heat of complete combustion per unit mass of volatiles liberated at the 

peak mass loss rate temperature Tp 

T Tp o dt

dm

m

1

=

is the maximum mass loss rate

The heat release capacity can be expressed as [64-66]: 

o

max

O

2

p

a

o

c,v

max

c

c m

1 C m

eRT

h h (1 )E 2

& ∆ &

β

μ

β η = − = = 2-3 

2-2
where β is the heating rate, μ is the char yield, and Ea is the activation energy, C = 419 

±19 kJ/mol-O2 = 13.1 ±0.6 kJ/g-O2 , and is the instantaneous mass consumption rate of 

oxygen at the peak pyrolysis rate. 

max

o2 ∆m&

According to equation 2-1, the total heat of combustion of pyrolysis gases can be calculated by 

summing the heat of combustion of all the volatiles released during the entire decomposition

process. In a similar way, the peak of heat release rate can be calculated from the maximum 

mass loss rate and the heat of combustion of the volatiles generated at that temperature,

according to equation 2-2. These two parameters calculated from pyrolysis GC/MS and STA 

results should be comparable to those directly measured from PCFC experiments based on the 

oxygen consumption principle. 

2.2.1 Calculation of the Composition of the Volatiles.

Although the qualitative analysis (or identification) of the decomposition products of most

known polymers has been already performed and published, little has been done on the 

quantitative analysis of the pyrolysis gases by using mass spectrometry (MS) as a detector. It is

because the total ionization current (TIC) signal from the MS does not directly correspond to the 

relative concentration of each volatile; neither does the area under each peak. There are relative 

response ratios (response factors) between them. Several models have been proposed to predict 

the response factors. One model presumes that only the total ionization cross sections of 

molecules are important in adjusting their total ion current differences. It has been found that 

equation 2-4 is valid for a large variety of molecules over a large range of pressure [68 and 69]. 

It = Q ⋅ I e ⋅ d ⋅ N 2-4

where It is the total ion current, Ie is the ionizing electron current, Q is the total ionization cross

section, d is the ionizing path length, and N is the concentration of the molecules. 

Because few total ionization cross-section values are available in the literature, a method to

predict the total ionization cross section is required. Fitch and Sauter [70] conducted a multiple 

linear regression analysis between the electron impact total ionization cross sections reported in 

the literature and the atomic composition. The regression equation is 

i i Q = 0.082 +∑a ⋅ n 2-5 

where ai and ni are the coefficient and number of each of the eight atom types, H, C, N, O, F, Cl, 

Br, and I (see table 2-1). 

TABLE 2-1. CROSS-SECTION REGRESSION COEFFICIENTS [70]

Atom C H O Cl Br I F N S

ai 1.43 0.73 1.10 3.98 5.19 6.62 0.61 1.20 3.80

2-3
The scheme is based on the additivity of atomic ionization cross sections. The coefficients for 

the calculation are determined by linear regression using 179 total ionization cross-section 

measurements taken from the literature. The largest errors are found in the group of inorganic 

gases. The average cross-section prediction error was found to be 4.69% by this approach. 

In this section, this method is used to estimate the total ionization cross section of each volatile 

and then to calculate its relative concentration according to equation 2-4. 

2.2.2 Calculation of Total Heat of Combustion and Heat Release Capacity of Polymers.

To calculate the total heat of combustion of polymers, the heats of combustion of all 

decomposition volatiles need to be known. It is not realistic to expect to find tabulated, 

experimental data on all organic compounds. Fortunately, the heat of combustion can be 

calculated from the heat of formation by using 

c p f p r f Hr ∆ H = ∑n ∆ H −∑n ∆ (2-6) 

where ∆fHp and ∆fHr are the heats of formation of products and reactants, respectively. The 

heats of formation of many simpler molecules have already been measured, and for more 

complex species, Benson’s group additivity method [71] was used to estimate their heats of

formation. 

f iH f ,i ∆H = ∑n (2-7) 

where Hf,i is the contribution of the ith group to the heat of formation. After the heat of 

formation of a molecule is determined, its heat of combustion can be calculated according to 

equation 2-6. Then the net heat of combustion of polymer can be estimated by using 

equation 2-8. 

∑

∑ = −

i i

i c ,i

c n M

n H

H (1 )

∆

∆ μ (2-8) 

where ni (mol%) is the molar fraction of the ith decomposition volatile, ∆Hc,i (kJ/mol) is the heat 

of combustion of the ith component, Mi (g/mol)is the molar mass of the ith component, and μ is 

the char yield (g/g) at final temperature. 

In addition, the maximum mass loss rate can be easily obtained from the derivative of TGA 

curves (DTG). Then, by analyzing the decomposition products at that temperature, the heat 

release capacity can be calculated according to equation 2-9 

β

∆

η

1

n M

n H

dt

dm

m

1

P

i

T T i i

c,i

max

o

⋅

















∑ ⋅

∑ = ⋅ ⋅

=

 (2-9) 

2-4
where 

max dt

dm (g/s) is the maximum mass loss rate

mo (g) is initial sample mass 

β (K/s) is the heating rate 

2.3 EXPERIMENTAL.

2.3.1 Pyrolysis GC/MS. 

The general configuration for pyrolysis GC/MS was the heated interface mounted on the top of 

the gas chromatography (GC) injection port. On the detection side of the GC (Hewlett-Packard 

5890 Series II), a mass selective detector (Hewlett-Packard 5972 Series) was used. The 

pyroprobe was a commercial device (Pyroprobe 2000, CDS Analytical) connected with a heated 

interface to the GC/MS. The probe was 6.4 mm in diameter containing a 3-mm-diameter, 

25-mm-long platinum resistance coil. The probe is capable of controlled linear heating rates

ranging from 2x10-2 to 2x104

 K/s, according to the manufacturer’s literature. The column was a

fused-silica capillary column (cross-linked 5% PH ME siloxane, 0.25 mm in diameter and 30 m 

long, Hewlett-Packard). 

The samples were pyrolyzed in the heated interface, and the pyrolysis products were flushed

directly into the column. The GC oven was then ramped at 10°C/min from 36°C to 295°C and 

held at that temperature for 15 min. The masses scanned ranged from m/z 11 to 500. 

Three pyrolysis conditions have been used: 

1. Pyrolyzing the sample to 930°C at a heating rate of 4.3°C/s and collecting all the 

decomposition volatiles (same conditions used in PCFC measurements). 

2. Pyrolyzing the sample to 930°C at 10°C/ms and collecting all the decomposition 

volatiles. 

3. Pyrolyzing the sample at 10°C/min to the temperature of maximum mass loss rate and

only collecting the decomposition volatiles at ±5°C of that temperature.

2.3.2 Simultaneous Thermal Analysis.

The thermal decomposition process of polymers was investigated by the Rheometric Scientific

Simultaneous Thermal Analyzer (STA 1500), which combines the complementary techniques of 

DSC and TGA in a single sample. It has a wide temperature range (ambient to 1500°C). 

Because it was assumed that the decomposition of polymers at a burning surface is anaerobic, all 

the experiments were done under a nitrogen atmosphere. To avoid mass and heat transfer 

effects, the sample weight was kept small, around 10 mg, and the heating rate was 10°C/min. 

2-5
2.3.3 Pyrolysis-Combustion Flow Calorimeter.

The detailed information about PCFC can be found in the literatures [64-66]. The PCFC 

contains the following major parts: pyrolyzer, combustor, gas scrubbers, flow meters, oxygen 

analyzer, and data acquisition system (figure 2-1). 

FIGURE 2-1. SCHEMATIC PICTURE OF PCFC [66]

The pyrolyzer consists of a temperature-controlled, heated stainless steel interface that can

accept a pyroprobe. The combustor was a coiled Inconel tube contained in a ceramic furnace

that can maintain a maximum temperature of 1200°C. The gas scrubbers were tightly packed 

anhydrous calcium sulfate (Drierite) and sodium hydroxide coated silica (Ascarite) to remove

H2O and CO2 from the flow stream after combustion. The oxygen analyzer was zirconia-based 

(Panametrics Series 350). The mass flow rate of pure nitrogen (82 cm3

/min) and oxygen (18 

cm3

/min) were controlled by the flow meters. 

Basic operation involves anaerobic pyrolyzing the sample and measuring the heat released by 

complete combustion of the volatiles using the oxygen consumption principle [64-66]. In a 

typical test, 1-milligram samples were introduced into the pyrolyzer in a quartz capillary tube.

The pyrolyzer interface temperature was slightly below the initial decomposition temperature to 

prevent condensation of high-molecular-weight thermal decomposition products. The sample

was pyrolyzed to 930°C at 4.3°C/s in pure nitrogen (pyrolysis). Then the volatiles were swept 

from the pyrolyzer, mixed with excess oxygen, and fed through a combustor at a preset 

temperature of 900°C to achieve complete combustion. Afterwards, Drierite and Ascarite were 

used to remove carbon dioxide, water, and acid gases from the combustion stream. Finally, the 

flow rate and oxygen concentration were measured and used to calculate the heat release rate and 

the heat of combustion of the sample. 

PCFC is a nonflaming combustion test. The heat release rate of the polymers can be calculated 

from the measured oxygen consumption after signal deconvolution to correct for flow dispersion. 

Then, the heat release capacity was obtained by dividing maximum heat release rate by the

sample weight and the heating rate. The total heat of combustion of the fuel gases per unit 

2-6
sample mass was obtained by direct integration of the heat release rate versus time. Char yield

was determined by weighing the sample before and after the test. The coefficient of variation of 

the heat release capacity was used to evaluate the repeatability of the experiments. 

2.3.4 Materials.

Oxygen and nitrogen gases for testing were of 99.99% purity grade, obtained from MerriamGraves Industrial Gases and Welding Products. About 25 polymers from Aldrich Chemical 

Company and Scientific Polymer Products as well as some research polymers were tested. All 

the samples were dried overnight at 100°C under vacuum and stored in a desiccator. The 

samples included high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), 

poly(α-methyl styrene) [P(α-M-S)] (Mn=960 g/mol), poly(tetrafluoroethylene) (PTFE) (Dupont 

Co.), poly(vinyl chloride) (PVC), polychloral (Prof. Vogl at UMass), poly(acrylonitrile) (PAN), 

poly(methyl methacrylate) (PMMA) (Mn=35,000 g/mol), poly(oxymethylene) (POM), 

poly(ethylene oxide) (PEO), poly(phenylene oxide) (PPO), Nylon 66, PC, poly(ethylene 

terephthalate) (PET), poly(butylene terephthalate)(PBT), poly(ether ether ketone) (PEEK), 

poly(phenyl sulfone) (PPhS), Kevlar 29 (Dupont Co.), Nomex

 (Dupont Co.), ULTEM (GE

Plastics), PI, PBZT (Dupont Co.), BPC II-polyarylate (Prof. Brzozowski in Warsaw University 

of Technology), and poly(hydroxyamide) (PHA) (Prof. Kantor at Umass). The chemical 

structures of some of the polymers are listed in figure 2-2. 

FIGURE 2-2. CHEMICAL STRUCTURES OF SOME POLYMERS 

2-7
2.4 RESULTS.

2.4.1 Thermal Stability and Decomposition Process of Polymers. 

It was suggested that oxygen from the surrounding atmosphere is usually completely consumed

in the flame zone so that the pyrolysis of the condensed-phase polymer takes place in the absence 

of oxygen [72 and 7]. In addition, recent work [64] shows that char yield in a fire is equal to the 

anaerobic pyrolysis residue at the flaming surface temperature, which suggests that the char 

formation takes place in an oxygen-free environment where solid-state oxidation reactions are 

slow compared to polymer dissociation and gas/char formation. Therefore, in this section, all the 

STA analyses were performed under nitrogen (N2). The derivative of TGA (DTG) curves, which 

indicate the mass loss rates of polymers, were obtained by differentiating the TGA curves. 

The thermal decomposition process is usually characterized by a number of experimental 

parameters [73]: (1) the temperature of initial decomposition, T99% or Tonset; (2) the temperature 

of the maximum rate of decomposition, Tmax, at which the mass loss rate is in maximum; (3) the

average of activation energy, Ea, determined from the temperature dependence of the rate of 

weight loss, assuming that the decomposition process is a first-order reaction; (4) char yield, the

solid residue left at very high temperature; and (5) heat of decomposition, ∆H, heat evolved or 

absorbed during decomposition. Table 2-2 summarizes several important parameters on the

thermal decomposition of some polymers. 

There are two temperatures that are usually used to characterize the initial decomposition of

polymers. One is the temperature at 1% weight loss, T99%. The other is the onset decomposition 

temperature, Tonset, which is determined by the extrapolation of two tangent lines of the TGA 

curve. Generally, Tonset is about 20°~50°C higher than T99%, depending on the slope of the 

weight loss curves. At Tonset, the polymers usually already had a large weight loss (about 10%). 

Therefore, Tonset does not really reflect the initial decomposition of polymers. In contrast, it is 

more reasonable to use T99% as the temperature to characterize the thermal stability of the 

polymers. However, T99% can easily be affected by the vaporization of water and solvents 

absorbed or the small molecule additives. Therefore, T95% is used by some people as a 

replacement. 

According to table 2-2, most aliphatic polymers (polymers with aliphatic backbones), especially 

the ones with bulky side groups such as PMMA and P(α-M-S), are less stable than wholly

aromatic polymers such as PI. However, there are some other important factors, such as 

secondary or van der Waals bonding forces, cross-linking, and multiple bonding, that can affect 

the thermal stability of polymers. For example, due to its high crystallinity, HDPE is much more 

stable than PET and PBT. It can also be seen that the char yield increases with the aromaticity of

the polymers. In addition, it was found that the temperature at the maximum of heat flow (peak 

of the DSC curve) is very close to the temperature at the maximum mass loss rate (peak of the 

DTG curve), which indicates that the heat and mass loss events during decomposition are 

interrelated.

2-8
TABLE 2-2. THERMAL DECOMPOSITION PROPERTIES OF POLYMERS 

Polymers 

T99%a

(°C) 

Max. Mass 

loss rate 

(103/s) 

Tmax

b

(°C) 

Tmax'

c

(°C) 

∆Hd

(J/g) 

Char 

Yield 

(%) 

Eae

(kJ/mol) 

∆Tf

(°C) 

PMMAg 167 2.06 370 371 687 0 254

46 

158 

147-170 

199-282 

312-412 

Poly(chloral) 194 1.19 221 277 380 0 - -

P(α-M-S)g 202 2.52 336 340 443 0 47

149 

155-285 

285-344 

PVCh 246 1.74 294 285 140 6 140

206 

183-300 

383-458 

PANh 283 5.0 310 291 -444i 39 158 240-313

POM 316 4.56 384 386 937 0 232 312-395

PS 336 5.29 417 418 683 0 289 351-420

PBT 350 4.18 404 402 281 0 298 331-411

PP 363 5.23 461 450 370 0 97

394 

316-376 

408-477 

Nylon 66 372 3.45 452 452 140 0 238 356-474

BPC IIpolyarylate 372 0.6 472 466 -302i 51 166 290-393

PET 382 3.70 440 432 174 8 281 347-450

PPO 397 2.48 456 461 150 23 306 417-453

HDPE 413 6.4 471 471 256 0 242

476 

387-452 

453-495 

PTFEh 456 2.9 573 579 447 0 247

368 

416-506 

537-588 

PC 448 3.8 514 478 111 17 298 430-520

PI 461 0.5 602 602 62 52 106 445-594

PPhS 481 1.71 573 - - 42 226 480-575

PHAh 250

586 

0.4 633 - - 56 43

366 

227-354

567-593 

Kevlar 513 1.96 576 578 228 31 368 515-571

PEEK 539 2.2 586 - - 46 512 530-576

PBZT 659 0.38 729 707 338 58 286 653-718

a Temperature at 1% weight loss 

b Temperature at maximum mass loss rate c Temperature at the peak of heat flow (determined from DSC curve)

d Heat of decomposition (determined from DSC curves) e Activation energy calculated according to TGA curves f Temperature range for Ea calculations g Several decomposition stages, depending on molecular weight h Two distinct decomposition stages i

 Exothermic decomposition peak

2-9
Figures 2-3 lists the STA (TGA/DSC) and DTG curves of several aliphatic polymers. It was 

found that most aliphatic polymers such as PP, HDPE, and PS decompose in a single stage with 

zero char yield, but some polymers such as P(α-M-S), PMMA, PVC, and PTFE decompose in 

more than one stage. In addition, the thermal decomposition processes of PMMA and P(α-M-S) 

also depend on their molecular weight. The effects of molecular weight on the decomposition of 

polymers will be discussed in detail in section 6. 

0 100 200 300 400 500 600

-0.8

-0.6

-0.4

-0.2

0.0

DTG

Deriv. of weight (

%/s)

Temperature (oC)

0

20

40

60

80

100

Weight (%)

-15

-10

-5

0

5

10

TGA

DSC

Heat flow (m

W)

0 100 200 300 400 500 600 700

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

DTG

Deriv. of weight (%/s)

Temperature (oC)

0

20

40

60

80

100

Weight (%)

-30

-20

-10

0

10

DSC

TGA Heat flow (m

W)

(b) (a) 

0 100 200 300 400 500

-0.3

-0.2

-0.1

0.0

DTG

Deriv. of weight (%/s)

Temperature (oC)

0

20

40

60

80

100

Weight (%)

-10

-5

0

5

10

TGA

DSC

Heat flow (mW)

0 200 400 600 800 1000

-0.4

-0.3

-0.2

-0.1

0.0

DTG

Deriv. of weight (%/s)

Temperature (oC)

0

20

40

60

80

100

DSC

TGA

Weight loss (%)

-10

-5

0

5

10

15

Heat flow (mW)

(c) (d) 

FIGURE 2-3. THE STA AND DTG CURVES OF ALIPHATIC POLYMERS 

(10°C/min IN N2) (a) HDPE, (b) PS, (c) PMMA, AND (d) PVC 

However, most aromatic polymers such as BPA-polycarbonate and (PPhS) usually have a major 

sharp weight loss with a certain amount of char left at high temperatures (figure 2-4). It is

believed that there are two stages corresponding to two types of decomposition reactions [73]. 

One takes place at relatively low temperatures involving chain scission reactions to form lowmolecular-weight fragments and gases. The other is the recombination reaction resulting from

the formation of final char, which happens at high temperatures. 

2-10
0 200 400 600 800 1000

-0.35

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

DTG

Deriv. of weight (%/s)

Temperature (oC)

0

20

40

60

80

100

DSC

TGA

Weight loss (%)

0

5

10

15

20

Heat flow (mW)

0 200 400 600 800 1000

-0.16

-0.12

-0.08

-0.04

0.00

DSC

DTG

Deriv. of weight (%/s)

Temperature (oC)

0

20

40

60

80

100

TGA

Weight loss (%)

0

5

10

15

20

25

Heat flow (m

W)

(a) (b) 

FIGURE 2-4. THE STA AND DTG CURVES OF AROMATIC POLYMERS 

(10°C/min IN N2) (a) PC AND (b) PPhS 

It was also found that the heat of decomposition for most polymers is endothermic, ranging from 

100 J/g to 900 J/g. For some aromatic high-temperature polymers, such as PEEK and PPhS 

(figure 2-4(b)), the heat events during decomposition are very complex. A baseline uplift is 

usually observed at the beginning of the decomposition of most charring aromatic polymers. 

However, the mechanism is not clear yet. 

A few polymers such as PAN and BPC II-polyarylate (figure 2-5) show an exothermic 

decomposition peak, but different mechanisms may be involved. For PAN, it is due to the 

cyclization reaction, while for BPC II-polyarylate, it is due to the formation of HCl and some

complicated cross-linking reactions. Most polymers with exothermic decomposition contain 

either halogens or some unsaturated double or triple bonds, which can lead to char formation by 

cross-linking or cyclization reactions. In general, the heat of decomposition is the consequence 

of several processes, such as bond dissociation, new bond formation, and volatile evaporation. 

0 200 400 600 800 1000

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

DTG

Deriv. of weight (%/s)

Temperature (oC)

0

20

40

60

80

100

TGA DSC

Weight loss (%)

0

10

20

30

40

50

60

Heat flow (m

W)

0 200 400 600 800 1000

-0.06

-0.04

-0.02

0.00

DTG

Deriv. of weight (%/s)

Temperature (oC)

0

20

40

60

80

100

TGA DSC

Weight (%)

0

5

10

15

20

Heat flow (mW)

(b) (a) 

FIGURE 2-5. THE STA AND DTG CURVES OF POLYMERS WITH EXOTHERMIC 

DECOMPOSITION (10°C/min IN N2) (a) PAN AND (b) BPC II-POLYARYLATE 

2-11
If the thermal decomposition of polymers is assumed to be a first-order reaction, the average 

activation energy, Ea, can be determined from the temperature dependence of the rate of weight 

loss according to equation 2-11. 

RT

E ) ln A

dt

dm

m

1 ln( a − ⋅ = − (2-11)

where m is the sample weight, dm/dt is the weight loss rate, A is the pre-exponential factor, R is

the gas constant, and T is the temperature. The calculated activation energies of some polymers 

are listed in table 2-2. 

It was found that for the polymers with low char yields such as HDPE, PS, and nylon 66 

(figure 2-6(b)), the assumption of first-order decomposition is applicable to almost the whole

major decomposition temperature range (about 70°C). However, for the high-charring aromatic 

polymers such as PC and PPhS (figure 2-6(c)), the valid temperature range is only from the

beginning to the middle of the major decomposition stage. Therefore, a first-order reaction

might not be a good kinetic model for the decomposition of some aromatic polymers, such as 

BPC II-polyarylate and PI, due to their intensive charring process at high temperatures. 

1.28 1.32 1.36 1.40 1.44 1.48 1.52

-10

-8

-6

-4

-2

T=453-495oC

Weight loss=90%

Ea=476kJ/mol

T=387-452o

C

Weight loss=10%

Ea L

=242kJ/mol n(-1/m x dm/dt)

1/T (x103/K)

(a) 

1.3 1.4 1.5 1.6 1.7

-12

-10

-8

-6

-4

-2

T=356-474oC

Weight loss=97%

Ea=238kJ/mol

Ln(-1/m x dm/dt)

1/T (x103/K)

1.10 1.15 1.20 1.25 1.30 1.35 1.40

-12

-10

-8

-6

-4

-2

T=480-575oC

Weight loss=35%

Ea

=226kJ/mol

Ln(-1/m x dm/dt)

1/T (x103/K)

(b) (c)

FIGURE 2-6. ACTIVATION ENERGIES OF THERMAL DECOMPOSITION 

CALCULATED BY TGA DATA (a) HDPE, (b) NYLON 66, AND (c) PPhS 

2-12
It is easy to understand that polymers with several decomposition stages have several activation

energies that correspond to different temperature ranges and weight losses. However, it is 

interesting that HDPE (figure 2-6(a)) and PP also have two activation energies, though they only 

show one distinct decomposition stage in TGA. The first Ea (97 kJ/mol for PP and 242 kJ/mol

for HDPE) corresponds to a low temperature range during which the polymers only have about

2%~10% weight loss. This is probably because the initial decomposition, which starts from the 

defects of the polymer chain, does not require a lot of energy. The second Ea (279 kJ/mol for PP

and 476 kJ/mol for HDPE) corresponds to the C-C main-chain scission of the polymers. 

Generally, the activation energies of different polymers are greatly dependent on their chemical 

structures, ranging from 100 kJ/mol to 500 kJ/mol. 

2.4.2 Thermal Decomposition Products of Polymers.

The total ion current pyrograms (TIC) of several polymers are shown in figures 2-7 through 2-9. 

For the polymers made by additional polymerization, there are two general types of 

decomposition: end-chain scission (depropagation or unzipping) and random-chain scission. 

The main decomposition product of P(α-M-S), POM, and PMMA (figure 2-7(a)) is the 

monomer. Therefore, the major decomposition mechanism is unzipping. The chain 

depolymerizes by successive release of monomer units from a chain end or at a weak link, which 

is essentially the reverse of chain polymerization. 

For Polyethylene (PE) and PP (figure 2-7(b)), the decomposition products are a series of alkenes, 

alkanes, and dienes. Therefore, the decomposition mechanism is random scission along the 

polymer chain, giving a mixture of hydrocarbons that are usually large compared with the

monomer unit. The decomposition products of PP are more complex because of the chain 

transfer reactions during pyrolysis. 

The main decomposition products of PS and PPO are monomer, dimmer, and trimer 

(figure 2-7(c)). Therefore, the decomposition mechanism is the combination of random scission 

and unzipping. 

However, for all the aromatic condensation polymers such as polyester and polyamide, when 

heated to high temperatures, the polymer chains usually randomly break at the heteroatom 

bridges (figure 2-8). They then decompose in varying degrees to carbonaceous char residue 

through a set of complex reactions involving cross-linking and bond scissions. Depending on the

chemical structure of the polymers, the major decomposition products usually include CO2, CO, 

and a series of aromatic phenols, amines, acids, ethers as well as some complicated

rearrangement compounds. 

It was found that when the polymers decompose under a faster heating rate, such as 10°C/ms,

they will release more low-molecule-weight fragments, but the types of the major decomposition 

products are essentially unchanged (figure 2-9). 

2-13
MMA (a) 

CnH2n and corresponding CnH2n-2, CnH2n+2

C14H28

(b) C10H20

C9H18

styrene 

(c) 

styrene trimer 

styrene dimer 

FIGURE 2-7. PYROLYSIS GC/MS TRACES OF ADDITIONAL POLYMERS 

(4.3°C/s TO 930°C) (a) PMMA, (b) PE, AND (c) PS 

2-14
OH

OH

OH

OH

C2H5 OH

OH

OH

(a) 

CO2, CO

SO2

CO2, CO 

OH

O

O

O

O

OH

O

OH

(b) 

FIGURE 2-8. PYROLYSIS GC/MS TRACES OF AROMATIC POLYMERS 

(4.3°C/S TO 930°C) (a) PC AND (b) PPhS 

2-15
C10H20

(a) 

C14H28 CnH2n and some CnH2n-2, CnH2n+2

C6H12

OH

OH

O

OH

(b) 

CO2 

CO 

FIGURE 2-9. PYROLYSIS GC/MS TRACES OF POLYMERS AT A FAST HEATING RATE

(10°C/ms TO 930°C) (a) HDPE AND (b) PC 

2.4.3 Flammability.

The PCFC results of different polymers are listed in table 2-3. It can be seen that aliphatic 

hydrocarbon polymers such as PE, PP, and PS are much more flammable than the polymers that 

contain aromatic, heteroaromatic rings, or heteroatoms (halogens, N, S, O etc.). This is because 

these aliphatic polyhydrocarbons can be completely decomposed at a rapid rate with no char and 

generate a lot of hydrocarbon volatiles with high fuel values. Aromatic polymers usually 

produce relatively high char yields. The char can reduce the amount and release rate of volatile 

2-16
fuels and act as a barrier for heat and mass transfer. Therefore, aromatic polymers generally

have lower flammability. However, this is not always true because the flammability is a function 

of both solid- and gas-phase chemistry. For example, PPO has a char yield of 23%, but it is 

much more flammable than PMMA whose char yield is zero. The high flammability of PPO is 

mainly due to its highly flammable decomposition volatiles—a series of phenols. PTFE and 

poly(chloral) also have very low flammability but zero char yield. The introduction of halogen 

atoms into polymer structures can efficiently reduce the flammability of the polymers because 

the halogenated decomposition volatiles have relatively low flammability and can also confer

some flame-retardant effect in the gas phase. The polymers (such as BPC II-polyarylate)

containing both halogens and aromatic structures have extremely low flammability. 

TABLE 2-3. FLAMMABILITY OF DIFFERENT POLYMERS (930°C AT 4.3°C/s) 

H. R. Capacity Total Heat Char Yield Cov.* 

Polymers (J/g-K) (kJ/g) (%) (%)

PP 1584 41 0 4.3

PE 1558 40 0 18.5

PS 1199 38 0 5.2

P(α-M-S) 730 37 0 6.7

Nylon 66 648 28 0 14.3 

PEO 580 23 4 4.0

PPO 553 22 23 8.2

PBT 420 22 0 8.5

PET 393 17 8 8.5

PC 382 19 17 9.3

PMMA 376 23 0 4.6

Kevlar 292 15 36 1.9

POM 261 14 0 8.8

PEEK 163 13 46 3.6

PPhS 156 12 39 2.5

ULTEM 121 12 49 8.3

PTFE 58 6 0 7.0

Nomex

 45 12 53 6.0

PHA 42 10 56 4.3

Poly(chloral) 33 5 0 5.0

PI 29 9 53 4.8

PBZT 24 5 58 11.0

BPC IIpolyarylate 12 4 51 3.2

*Coefficient variation of heat release capacity. 

2-17
Generally, if the heat release capacity of a material is below 100 J/g-K, it is fire resistant. It can 

be seen that PHA, PI, PBZT, and BPC II-polyarylate are all fire-resistant polymers. Their

extremely low flammability is attributed to the following features: high thermal stability, high 

char yields, low maximum mass loss rate, and the ability to release flame-retardant molecules,

such as water and HCl. In all, the high degree of aromaticity (which can promote formation of 

highly cross-linked carbonaceous char), combined with the inclusion of heteroatoms such as 

halogen, N, and S (which, on thermal decomposition, gives products with low heat of 

combustion), can greatly improve the fire resistance of materials. 

Normally, the cov. of the heat release capacity of all the polymers measured is within 10% 

except for PE and nylon 66. The systematic error for the total heat released is 1 kJ/g. Under 

standard conditions, the PCFC method is very precise and highly reproducible. Moreover, it is 

applicable to a wide variety of materials (plastics, films, textiles, etc.). So far, it is probably the

most valuable flammability test for research materials, though it will never totally replace the

other fire tests. One special advantage of this method is that it gives numerical results that can 

capture some intrinsic relations between a material’s chemical structure and its flammability. 

2.4.4 Bond Dissociation Energies of the Polymers.

The B3LYP density-functional method [74 and 75] with a standard polarized split-valence 6-

31G(d) basis set [76] was used for the calculation of bond dissociation energies of the polymers. 

The method was chosen to achieve the maximum accuracy with a reasonable computational 

time. The restricted version of the method was used for closed-shell species, while the 

unrestricted version was used for radicals. The energies were obtained by calculating enthalpies 

of the bond dissociation reactions of some small model compounds with the same structure as 

the polymers. The computed energies of optimized structures of model compounds and their 

radical fragments were corrected for zero-point energy contribution. All the calculations were 

carried out using the Gaussian 98 package of programs [77]. The results of the calculations are 

shown in table 2-4. 

It is found that the weakest bond in HDPE, PP, PS, and PMMA is the main chain C-C bond. 

Therefore, these polymers prefer to break along the polymer main chain rather than to strip any 

side groups, and their major decomposition products contain intact monomer units such as 

monomer and oligomers. However, the introduction of side groups will inevitably weaken the 

strength of the C-C backbone. As a result, the thermal stability of PP, PS, and PMMA is lower 

than HDPE. For condensation polymers, the weakest bond is usually located around the 

heteroatomic linkage such as ether, ester, amide, and sulfone groups. However, there are usually 

several bonds whose strength is very close to the weakest bond. As a result, the decomposition 

of most condensation polymers is probably initiated by the breakdown of several different bonds 

around the same temperature. 

According to table 2-4, except for PE, PP, BPC II-polyarylate, and nylon 66, the decomposition

activation energies of the other polymers measured by TGA are all relatively close to the bond 

dissociation energies of their weakest bonds if the computational uncertainty is considered. This 

result suggests that the initial breakdown of these polymers is mainly caused by the rupture of 

the weakest bonds in the polymer chain. 

2-18
TABLE 2-4. BOND DISSOCIATION ENERGIES OF POLYMERS 

Polymers 

Bond Dissociation Energiesa

(kJ/mol) 

Ea

b 

(kJ/mol) 

Weight Lossc

(%) 

PE 242 

476 

10 

90 

PP 128 

394 

1.5 

87 

PS 289 75%

PMMA 

254 

46 

158 

1 

20 

63 

PET 281 78

PC 298 55

BPC IIPolyarylate 166 5

Nylon 66 238 97

Kevlar 368 22

PPhS 226 35

CH2 CH2

343

CH2 CH

318

330

CH3

CH2 CH

272

376

CH2 C

CH3

COOCH3

339

288

330

CH2 CH2 O C

O 355 330 393 426

O C

O

C

CH3

CH3

O C

O

309

251

385 293

C

C

O C

O

Cl Cl

385 293 426

330

389

O C

O

CH2 CH2 N

H

C

O

CH2 CH2

318 347 359 318 330

N

H

C

O

443 318 397

NH C

O

O S

O

O

O

464 311 293 276

a B3LYP density-functional method with a standard polarized split-valence 6-31G(d) basis set. The mean error 

is 33kJ/mol

b Calculated by TGA data

c

Weight loss corresponding to the temperature range for Ea calculated (refer to table 2-2)

2-19
However, it seems that the correlation between bond dissociation energy and activation energy is

not very simple because sometimes the activation energy calculated from TGA data does not 

directly correspond to the dissociation of one specific bond, but it is due to the breakdown of 

several bonds. In addition, the assumption of first-order decomposition is not valid for all 

polymers, especially high-charring aromatic polymers. 

It was also found that the bond dissociation energies of ester or amide linkage in condensation 

polymers are greatly dependent on the structures of the chemical units, which are linked to the

nitrogen or oxygen atom (table 2-5). If an aliphatic unit is connected to the nitrogen or oxygen, 

the bond dissociation energies are 360 kJ/mol for amide linkage and 390 kJ/mol for ester linkage. 

If it is an aromatic unit, the bond dissociation energies are lower (318 kJ/mol for amide linkage 

and 293 kJ/mol for ester linkage). It seems that the ester and amide linkages in wholly aliphatic 

structures are much stronger than those in wholly aromatic structures. However, the bond 

dissociation energies of the weakest bonds in all polyamides with different aliphatic-aromatic 

structure combinations are about the same (318 kJ/mol), though they are related to different 

types of bonds. 

TABLE 2-5. BOND DISSOCIATION ENERGIES IN ALIPHATIC-AROMATIC POLYMERS 

These bond dissociation energy calculations seem contradictory to the TGA results, which show 

that polymers with aliphatic structures usually have lower thermal stability than those with 

aromatic structures. For example, Kevlar and nylon 66 are polyamides and have the same

weakest-bond dissociation energies, but Kevlar is much more thermally stable than nylon 66, 

according to TGA analyses (figure 2-10). It is because in TGA measurements, the thermal 

stability is characterized by the temperature at which the polymers start to lose weight. If a 

polymer chain is already broken at several points, but without obvious weight loss, the TGA 

curve will not change at all. Therefore, TGA results will not reflect the initial breakdown of 

2-20
polymers unless there is a significant weight loss. For aliphatic polymers, after the 

decomposition is initiated by bond scission, low-molecule-weight volatiles that can be easily 

evaporated are produced. However, aromatic polymers usually form relatively large aromatic 

fragments that can be kept in solid state for a longer time and sometimes further recombine into 

more condensed structure. Thus, a significant weight loss can only be observed at high 

temperatures. As a result, the weight loss in aliphatic polymers is more detectable compared to 

aromatic polymers. In all, the lower-thermal stability of aliphatic polymers measured by TGA 

does not necessarily mean that the bonds in aliphatic polymers are weaker than those in aromatic

polymers. 

0 200 400 600 800

0

20

40

60

80

100

nylon 66

Kevlar

Weight (%)

Temperature (oC)

FIGURE 2-10. THE TGA CURVES OF KEVLAR AND NYLON 66

2.4.5 Flammability Calculated by Pyrolysis GC/MS and STA Results.

According to the procedures described earlier, the heat release capacity and total heat of 

combustion of the polymers can be calculated by combining the pyrolysis GC/MS and STA 

results. In table 2-6, the calculated values are compared to the experimental values from PCFC. 

The total heat of combustion calculated in the table is the total net heat of combustion, which is 

obtained by using the gross heat of combustion minus heat of vaporization of water produced 

during combustion. The gross heat of combustion is the standard molar enthalpy (heat) of 

combustion at 298.15 (K), and the products of combustion are taken to be CO2 (gas), N2 (gas),

and H2O (liquid) in their standard states. There are several error sources during calculations; for

example, some peaks in GC/MS pyrograms are difficult to identify, some peaks are overlapped

and difficult to separate, and some of the small peaks (molar concentration smaller than 5%) are

neglected in the calculations. In addition, the relative electron impact total ionization cross 

sections for the decomposition volatiles are estimated by an empirical equation. The heat of

combustion for some complicated compounds are also estimated by using Benson’s law. 

Considering all these possible errors, one can see that the different methods correlate to each 

other very well, which indicates that the thermal decomposition process and decomposition

2-21
volatiles are two important factors in determining the polymer flammability. It can also be seen 

that the char yield obtained by STA is very close to PCFC, though different heating rates are 

used in these two methods. 

TABLE 2-6. CORRELATION BETWEEN DIFFERENT METHODS

Heat release Capacity

(J/g-K) 

Total Heat Released 

(kJ/g) 

Char Yield at 930°C

(%) 

Polymers Calculated a PCFC b Calculated c PCFC b STA d PCFC b

PE - 1558 45 40 0 0

PP - 1584 45 41 0 0

PS 1277 1199 41 37 0 0

P(α-M-S) 695 730 41 38 0 0

PPO 635 553 22 22 23 23

Nylon 66 509 648 21 28 0 0

PC 470 382 19 19 17 22

PET 407 393 16 17 8 5

PMMA 345 376 24 23 0 0

POM 233 261 17 14 0 0

PEEK 211 163 11 13 46 46

Kevlar 207 292 16 15 32 36

PHA - 42 9 10 56 57

Poly(chloral) 34 33 5 5 0 0

PI 31 29 6 9 50 53

a Calculated by measuring the maximum mass loss rate and collecting the decomposition volatiles at

maximum mass loss temperature (heating rate, 10o

C/min)

b Pyrolyze at 4.3o

C/s to 930oC 

c Calculated by pyrolyzing the polymer at 4.3o

C/s to 930oC and collect all the decomposition volatiles 

d Heating rate 10o

C/min

2.4.6 Flammability Estimated by Using Chemical Structure and TGA Results.

If complete combustion of all the volatiles released during polymer decomposition is achieved, 

the net heat of combustion of polymers can be estimated by two simple calculation methods. 

One is based on the oxygen consumption principle, which is also exploited in both PCFC and 

cone calorimeter tests. The amount of oxygen needed for complete combustion of the structural 

unit can be calculated according to the stoichiometry of the combustion equation. The second 

method is based on the additivity of contributions of the individual atoms comprising the

polymers. In this calculation, only the heats of combustion of carbon and hydrogen were 

2-22
considered so as to simplify the calculation. All the oxygen atoms in the polymers were 

excluded by combustion with hydrogen atoms to form H2O, which will not contribute to the heat

of combustion during calculations. As a result, the effective number of hydrogen atoms used in

the calculations was less than that in the formula for oxygen-containing polymers. Other

heteroatoms, such as N, S, P, and halogens, were assumed to have no contribution to the heat 

released. Therefore, they have no fuel values, but only add dead weight to polymers. In both 

methods, char yields were used to adjust the net heat of combustion in terms of per unit mass of 

solid polymers. They can be either measured by TGA or calculated by molar group additivity. 

All the char yields used here were measured by TGA. 

The principles of the two calculation methods for estimation of net heat of combustion are 

summarized below. 

Combustion equation: 

H O( g ) B(s) y )O ( g ) xCO ( g ) y z C H O B(s) ( x x y z + + − 2 → 2 + 2 +

4 2 2

C(s) O ( g ) CO ( g ), H ( C ) c + 2  →  2

∆ H ( g ) O ( g ) H O( g ) H ( H ) c

2 2 2

2

2

1

+  → ∆ 

Method 1: Oxygen consumption principle 

( char fraction ) M(C H O B )( g / mol )

)( mol O / mol ) ( kJ / mol O ) y z ( x

H (C H O B )( kJ / g )

x y z

c x y z × −

+ − − × −

∆ = 1

419

4 2 2 2

Method 2: atom t additivity principle 

( char fraction ) M(C H O B )( g / mol )

x H (C )( kJ / mol ) ( y z ) H ( H )( kJ / mol )

H (C H O B )( kJ / g )

x y z

c c

c x y z × −

∆ + − ∆

∆ = 1

2

2

1 2

in which M is the molecular weight of the repeating unit, ∆Hc(C) is the heat of combustion of 

carbon atom, and ∆Hc(H2) is the heat of combustion of hydrogen. 

2.4.6.1 Net Heat of Combustion of Polymers.

The two methods, oxygen consumption and atom additivity, have been used to calculate the 

gross heats of combustion of 48 small molecule organic compounds (appendix A, table A-1). 

The net heat of combustion obtained directly by the oxygen consumption principle has been 

converted to gross heat of combustion by considering the heat of vaporization of the water. It 

was found that the calculated values are very close to the reference values [78] (figure 2-11). 

The average relative deviations are ±6% for the oxygen consumption method and ±9% for the 

atom additivity method. Both methods are insensitive to the structure differences between 

compounds with the same formula because they did not consider the interactions between atoms. 

2-23
0 1000 2000 3000 4000 5000 6000

0

1000

2000

3000

4000

5000

6000

y=x

Calculated values (kJ/mol)

Reference values (kJ/mol)

(a)

0 1000 2000 3000 4000 5000 6000

0

1000

2000

3000

4000

5000

6000

y=x

Calculated values(kJ/mol)

Reference values (kJ/mol)

(b)

FIGURE 2-11. CALCULATION OF GROSS HEAT OF COMBUSTION OF SMALL 

ORGANIC COMPOUNDS (a) OXYGEN CONSUMPTION AND (b) ATOM ADDITIVITY 

The net heats of combustion of 35 polymers were also calculated by both methods (appendix A, 

table A-2). The calculated values were compared with PCFC results (figure 2-12). It can be

seen that the calculated values correlate relatively well with the experimental values. The 

standard deviations are ±3kJ/g for both methods. However, for nylon 66, Chalcon II-polyarylate, 

Xydar, PBZT, and some halogen-containing polymers such as BPC II-polycarbonate and BPC 

II-polyarylate, the accuracy is not as good, and deviations up to 6-7 kJ/g may occur. The reason

for this discrepancy arises, in large, apart from the assumptions used in these calculations. First,

the composition of the char is assumed to be the same as the original polymer, so its effect on the 

heat of combustion can be easily estimated by a linear weight reduction. However, the char has 

a more condensed structure and contains more carbons and less hydrogens than the original 

polymer. Therefore, to improve the accuracy, the elemental composition of the char should be 

identified. Second, contributions of the heteroatoms, such as S, P, and halogens, were 

2-24
completely neglected in calculations because their heats of combustion are usually very low. 

However, for some polymers, this simplification might not be appropriate because these 

heteroatoms might interact with the other atoms and have further effects on the polymer

flammability. Aside from these limitations, the atom additivity is found to be a fair 

approximation for estimating net heat of combustion of different polymers. Although the heat of 

combustion of polymers greatly depends on the number and heat of combustion of each type of

atom present, it is also greatly dependent on their internal bonding between atoms that will 

significantly affect their char yield measured by TGA. However, such interactions cannot be

handled by simple atom additivity. 

0 10 20 30 40 50

0

10

20

30

40

50

y=x

P

CFC (kJ/g)

Calculated values (kJ/g) 

(a)

0 10 20 30 40 50

0

10

20

30

40

50

y=x

PCFC (kJ/g)

Calculated values (kJ/g)

(b)

FIGURE 2-12. COMPARISON OF CALCULATED NET HEAT OF COMBUSTION OF 

POLYMERS WITH PCFC RESULTS (a) OXYGEN CONSUMPTION AND 

(b) ELEMENT ADDITIVITY 

2-25
The calculations based on atom additivity also show that hydrogen atoms have the biggest 

contribution to the heat of combustion of polymers due to its high fuel value and low weight.

Therefore, they are the major burning sources of polymers. On the contrary, the heteroatoms are 

usually heavier than carbon and hydrogen atoms, but they do not produce a lot of heat when 

burned. Therefore, any units that have low hydrogen to carbon ratio (H/C) and high content of 

heteroatoms are ideal structures for fire-resistant polymers. The low H/C ratio is usually 

achieved by introducing the aromatic or heteroaromatic ring structures, which can also increase 

the thermal stability and char yields of the polymers. 

2.4.6.2 Heat Release Capacity.

If the instantaneous heat of combustion per unit mass of the volatiles remains constant during 

decomposition, the heat release capacity should be proportional to its maximum mass loss rate 

and can be estimated by the following equation 

Heat release capacity (J/g-K) = Total heat released (J/g) * Max. mass loss rate (/s)/Heating rate 

(K/s) 

According to table A-2 in appendix A and figure 2-13, the correlations between calculated heat

release capacities with those from PCFC measurements are relatively good. The average relative 

deviations are about ±20% for both methods. The large discrepancies are mainly due to three 

reasons. (1) The decomposition volatiles released at different temperatures are different. 

Therefore, the heat released at a certain temperature might not be simply proportional to the mass

loss rate at that temperature. It is also greatly determined by the heat of combustion of the 

volatiles released at that temperature. (2) It is difficult to measure the maximum mass loss rate 

very accurately by TGA. (3) The errors in the term of total heat of combustion might be 

transferred to the calculation of heat release capacity and sometimes magnified by the high mass 

loss rates. As a result, the most serious deviations occur with Chalcon II-polyarylate, Xydar, 

and especially some halogen-containing polymers such as PTFE, BPC II-polycarbonate, and 

BPC II-polyarylate. The deviations of PTFE, BPC II-polycarbonate, and BPC II-polyarylate are 

not included when calculating average relative deviation. 

It can be seen that the heat release capacity, which is proportional to the maximum heat release 

rate, is greatly dependent on two parameters: maximum mass loss rate and heat of combustion 

of volatiles at that temperature. The mass loss rate, in turn, is greatly dependent on the char 

yield. Therefore, enhancement of char formation is very important in reducing both net heat of 

combustion and heat release rate. 

2.4.6.3 Char Yield. 

The char formation tendency is also greatly determined by the structure of polymers. It was 

found that char yields can be roughly estimated by molar group additivity [73]. In the research,

it has been observed that there are some simple correlations between char yield and the molar 

fraction of the effective char-forming atoms in the polymers (table A-3 in appendix A and 

figure 2-14). The effective char-forming components are identified as (1) main chain aromatic 

carbon atoms that are not separated by long aliphatic spacers such as –(CH2)n - (n >2), (2) C, N,

S in heteroaromatic rings, and (3) double or triple bonds such as C=C, C=S, C=N in main chain 

2-26
that are also conjugated with aromatic rings. Due to the existence of isopropyl groups that are 

easily broken apart, the number of effective char-forming atoms in bisphenol A structure is 

reduced to 6 compared with the 12 aromatic carbons in the polymer. 

0 200 400 600 800 1000 1200 1400 1600 1800

0

200

400

600

800

1000

1200

1400

1600

1800

y=x

P

C

F

C (J/g-K)

Calculated heat release capacity (J/g-K)

(a)

0 200 400 600 800 1000 1200 1400 1600 1800 2000

0

200

400

600

800

1000

1200

1400

1600

1800

2000

y=x

PCFC (J/g-K)

Calculated heat release capacity (J/g-K)

(b)

FIGURE 2-13. COMPARISON OF CALCULATED HEAT RELEASE CAPACITY OF 

POLYMERS WITH PCFC RESULTS (a) OXYGEN CONSUMPTION AND 

(b) ELEMENT ADDITIVITY 

2-27
0 20 40 60 80 100

0

20

40

60

80

100

y=0.89x R=0.83

Effective char-forming atoms (mol%)

Char yield (%)

FIGURE 2-14. CORRELATION BETWEEN CHAR YIELD AND MOLAR FRACTION OF 

EFFECTIVE CHAR-FORMING ATOMS IN POLYMERS

It can be seen that the molar fraction of the effective char-forming atoms is a reasonable measure 

for estimating the char yields of the polymers, although big deviations are observed in several 

polymers such as PPO, PI, Kevlar, PBZT, poly(amide-imide), and PES. The discrepancies are 

due to the following reasons. The proposed method is only based on the independent 

contributions of some individual atoms, but it does not include the interactions between different 

atoms, which are actually very important during the char formation process. For example, the 

alkyl substituents and ether linkages might greatly reduce the effectiveness of the aromatic 

carbons on char formation. The carbonyl groups in PI might be easily released as volatile CO; 

therefore, they might not contribute to the char formation, though they are in a heterocylic 

structure. In addition, some errors might come from TGA measurements, which is usually 

around 2%. Despite all these limitations, several structures, such as aromatic rings,

heteroaromatic rings, and some conjugate systems, are found in the major structures that can 

promote char formation. 

2.5 DISCUSSION.

Polymer thermal decomposition and flammability were evaluated by pyrolysis GC/MS, STA, 

and PCFC methods. There was good agreement between the different methods. Several 

important parameters can determine the ease of polymer combustion, including thermal stability, 

mass loss rate, the nature and properties of the decomposition products, and the char yield. Most

polymers decompose in a single step by a random chain-scission mechanism. Some polymers 

such as PMMA, P(α-M-S), and POM decompose by an unzipping mechanism. The heats of 

decomposition for most polymers are endothermic, ranging from 100 to 900 J/g. A few 

polymers, such as BPC II-polymers and PAN, show an exothermic peak. The maximum mass 

2-28
loss rate and the heat of combustion of volatiles are important factors in determining the heat 

release capacity. In addition, the quantum computation results show that there is no simple 

correlation between bond dissociation energy and activation energy calculated from TGA data. 

The relatively low thermal stability of aliphatic polymers is mainly due to the easy release of 

small molecular volatiles, which can be easily detected by TGA. The net heat of complete

combustion and heat release capacity of polymers can be successfully estimated by both oxygen 

consumption and atom additivity principles. The calculated results from both methods correlate 

relatively well with the PCFC experimental results. It was found that nonburning heteroatoms

such as O, N, S, P in polymer structures play an important role in reducing the total heat of 

combustion because these atoms only add mass without adding significant heat. Aromatic rings, 

heteroaromatic rings, and any units that can lead to the formation of fused-aromatic ring

structures will contribute to the char formation. Generally, the ideal fire-resistant polymers 

should have the following characteristics: high decomposition temperature, high char yield, low 

amount and release rate of volatile fuels and low heat of combustion of these fuels, endothermicphase transition or decomposition, and release of chemical flame-retardant molecules, such as

halogen and water. In all, introducing condensed aromatic or heteroaromatic rings and

heteroatoms (halogen, N, S, O, P, Si, etc.) is the basic way to reduce polymer flammability. 

2-29/2-30
3. LOW FLAMMABILITY AND THERMAL DECOMPOSITION OF POLY

(HYDROXYAMIDE) AND ITS DERIVATIVES.

3.1 INTRODUCTION. 

PBOs, which consist of alternating phenylene and condensed aromatic heterocyclic rings, have 

not only good chemical resistance, high modulus, and high strength but also high thermal 

stability and low flammability [79-81]. The first PBO was synthesized by Brinker and coworkers [82]. Later, Moyer and Kubota reported the preparation of fully aromatic PBOs by 

polycondensation reactions to yield the precursor PHA, followed by thermal cyclodehydration to

poly(benzoxazole) structures [83 and 84]. However, these PBO polymers are infusible and are

soluble only in concentrated sulfuric acid and polyphosphoric acid, so they are difficult to 

process. Thus, high costs of the finished polymers and of specialized fabrication techniques 

greatly limit their applications. Later, the effects of introducing hinge atoms or groups into the 

polymer chain were investigated to increase their flexibility. For example, incorporation of 

fluorinated linking groups into the polymer backbone enhanced solubility, while good thermooxidative stability and high glass transition temperature were retained [85 and 86]. Hsiao and 

Dai [87] also synthesized a new aromatic poly(ether benzoxazoles) via the introduction of 

diphenoxy benzene units into the polymer backbone, which greatly improved the solubility. 

However, very little research has been performed on the precursor PHAs. Pearce, et al. have

reported detailed investigations on the syntheses, thermal properties, and oxygen index of a 

series of wholly aromatic polyamides based on substituted and unsubstituted m- or p- phenylene 

diamine with both isophthaloyl and terephthaloyl chlorides [88-92]. Pearce, et al. found that the 

ortho-, halogen-, nitro-, and cyano-substituted polyamides produce the highest char yield, which 

are due to cross-linking at high temperatures and the formation of thermally stable benzoxazole 

rings [93-98]. The amount of PBO structure formed was dependent on the nature of the 

substituents. The more electron-withdrawing the substituent (e.g., F or NO2), the more 

benzoxazole structure is formed. Recently, Kantor, et al. [99] have synthesized a highmolecular-weight poly(3,3’-dihydroxy-biphenyl-isophthalamide) (PHA) as well as a series of

halogen, methoxy, phosphinate, and phosphate derivatives. It was found that this PHA cannot 

only cyclize into fire-resistant PBO, but also absorb some heat and liberate noncombustible 

water vapor during cyclization [100 and 23]. In addition, all these polymers show a very good 

solubility in aprotic solvents such as N-methylpyrrolidinone (NMP), N,N-dimethylacetamide 

(DMAc), and N,N-dimethylformamide. Therefore, they are potential candidates as solventprocessable, fire-resistant polymers for many high-performance applications. 

In this section, the low flammability of poly(hydroxyamide) (PHA) and its halogen, methoxy, 

phosphinate, and phosphate derivatives was characterized by multiple analytical techniques, 

emphasizing that the thermal decomposition behavior is the basis for the polymer flammability.

Pyrolysis gases from these polymers were identified by GC/MS. The residual chars were 

characterized by Fourier Transform Infrared Spectroscopy (FTIR) and elemental analysis. STA 

was applied to study the thermal decomposition process, and flammability was measured by 

PCFC. Halogens, phosphonates, and phosphates were examined because of their expected

flame-retardant effects, while methoxy derivatives were examined because of their easy 

syntheses. Thermal decomposition mechanisms were also proposed for these polymers. 

3-1
3.2 EXPERIMENTAL.

3.2.1 Materials. 

The chemical structures of PHA and its derivatives (figure 3-1) are given below. All the samples 

were supplied by Jungsoo Kim at the University of Massachusetts, Amherst [101]. 

FIGURE 3-1. STRUCTURES OF PHA AND ITS DERIVATIVES 

3-2
3.2.2 Film Preparation.

PHA-1 was dissolved in DMAc at room temperature with 1 wt% of LiCl. The polymer solution 

was coated onto a glass plate and dried in a vacuum oven at 100°C for one day. While still on 

the glass plate, the film was then cleaned in an ultrasonic cleaner three times for 30 minutes each 

time. Afterwards, the film was dried again in a vacuum oven at 120°C for one day. The film 

was then used for IR analysis. 

3.2.3 Characterization.

The thermal decomposition process was examined under N2 or air by a TA Instruments 2050 

TGA. STA was also performed under N2 with a Rheometric Scientific STA 1500 to study the 

mass change and the heat absorbed or evolved during the decomposition at high temperatures. 

Char yield of the polymers is defined here as the percentage of solid residue at 930°C under N2. 

Sample weights for all the thermal analyses were approximately 10 mg, and the heating rate was 

10°C/min. 

Flammability of all the polymers was measured with PCFC. Samples of 1.0 ±0.1 mg were 

pyrolyzed in a commercial device (CDS Pyroprobe 2000) to 930°C at 4.3°C/s under N2. The

volatiles were continuously swept away by a N2 flow, mixed with a metered flow of O2, and 

completely combusted at 900°C. The consumption rate of O2 was continuously measured. The 

heat release results were taken as the average of five measurements for each sample. The 

coefficient of variation of heat release capacity is around 10%, and the systematic error for total 

heat released is around 1 kJ/g. 

Composition of the volatiles was analyzed by pyrolysis GC/MS. Samples of 0.2~0.3 mg were

pyrolyzed under the same conditions used in the PCFC measurements (4.3°C/s to 930°C). The 

volatiles from pyrolysis were then separated by a Hewlett-Packard 5890 Series II gas 

chromatograph and analyzed by a Hewlett-Packard 5972 series mass spectrometer. A fusedsilica capillary GC column (cross-linked 5% PH ME siloxane, 0.25 mm in diameter and 30 m 

long) was used. The GC oven was programmed from 36° to 295°C at a heating rate of 10°C/min 

and then held at 295°C for 15 minutes. Masses were scanned from m/z 11 to 550. 

Transmission IR spectra were recorded on a Bio-rad FTS 175C FTIR instrument. The samples

for IR analyses were prepared by heating the solution-cast films to desired temperatures at

10°C/min under N2 in a TGA furnace. 

Elemental analyses were obtained on a Control Equipment Model 240XA elemental analyzer. 

3.3 RESULTS.

3.3.1 Thermal Stability and Decomposition Process of PHAs. 

Table 3-1 summarizes the thermal decomposition properties of PHA and its derivatives. The 

following discussion examines the details of the different decomposition behavior. 

3-3
TABLE 3-1. THERMAL DECOMPOSITION OF PHA AND ITS 

DERIVATIVES IN N2 

Polymers ηinha

T99%

b

(°C) 

T2

c

(°C) 

∆W1

d

(%) 

∆H1

e

(J/g) 

∆Tf

(°C) 

PHA-1 0.60 250 586 11 116 240-383

PHA-2 - 290 622 10 145 270-456

PHA-3 0.49 240 485 13 106 250-400

PHA-4 - 284 515 12 110 260-430

PHA-5 0.25 274 508 8 104 245-356

PHA-6 - 282 501 7 108 260-360

PHA-7 0.62 363 591 37 - 363-469

PHA-8 0.70 240 592 6 105 240-335

PHA-9 - 218 574 7 33 230-310

PHA-10 0.44 270 640 45 - 210-500

PHA-11 0.55 300 606 56 - 270-545

PHA-12 - g 182 651 16 72 180-360

PHA-13 -

 g 200 654 21 106 180-306

PHA-14 -

 g 184 652 23 121 180-370

a 0.5g/dl in NMP at room temperature 

b Temperature at 1% weight loss c Onset decomposition temperature of the last stage 

d Weight loss during the first stage e Heat absorbed during the first stage f Temperature range of the first stage g Polymers are only partially soluble in NMP 

TGA results of PHA-1 and 2 are shown in figure 3-2. It can be seen that they all decompose in 

two distinct and well-separated stages. The temperature at 1% weight loss (T99%) of PHA-1 

(250°C) is lower than PHA-2 (290°C). This difference indicates that PHA-2 (para) is more

thermally stable than PHA-1 (iso) due to its regular symmetric structure. X-ray diffraction 

results (figure 3-3) proved that PHA-2 has a higher crystallinity than PHA-1. 

It was found that the thermal decomposition process, flammability, and decomposition products 

of corresponding iso- and para-type PHAs are similar to each other, except para-PHAs have 

higher thermal stability. Only the flammability and thermal decomposition properties of isoPHAs are discussed below. 

3-4
50

60

70

80

90

100

Weight (%)

0 200 400 600 800 1000

Temperature (°C)

––––––– PHA-1 (iso)

– – – – PHA-2 (para)

FIGURE 3-2. TGA CURVES OF PHA-1 AND 2 IN N2

0 5 10 15 20 25 30 35 40

1000

2000

3000

4000

5000

6000

7000

8000

PHA-1

PHA-2

Intensity

2 Theta (

o

C)

FIGURE 3-3. X-RAY DIFFRACTION OF PHA-1 AND 2

The thermal decomposition processes of PHA-1 and its derivatives under N2 are shown in 

figure 3-4. 

According to figure 3-4(a), PHA-1 lost about 11% weight in the first decomposition stage 

(250°~383°C), which agrees very well with the calculated water loss due to the cyclization 

reaction (11.5%). The second stage (586°~821°C) is associated with a further 30% weight loss

due to the extensive breakdown of the PBO backbone. The weight loss then levels off, 

producing a high char yield of 56%. 

Halogenated PHAs (PHA-3 and 5) also decompose in two stages, which is similar to PHA-1 

(figure 3-4(a)). Introduction of bromine groups in PHA-3 slightly decreases the thermal stability 

of the first stage (240°C). In contrast, trifluoromethyl groups have the effect of increasing the 

thermal stability of PHA-5 (274°C). However, the onset decomposition temperature of the 

second stage is greatly reduced in both polymers [PHA-3 (484°C) and PHA-5 (508°C)] 

compared with PHA-1 (586°C). This is because the halogenated PBOs formed at the end of the 

first stage are less stable. At high temperatures, the halogen groups can be easily stripped away 

from the polymer main chain before any backbone scission. 

3-5
0 200 400 600 800 1000

20

40

60

80

100

 PHA-1 (-OH)

 PHA-3 (m-Br)

 PHA-5 (m-Br, -CF3)

Temperature (oC)

Weight (

%)

(a) 

0 200 400 600 800 1000

40

50

60

70

80

90

100 PHA-7 (-OMe)

 PHA-8 (-OMe, -OH)

 PHA-9 (-OMe, -OPO2(OMe)

2)

Weight (%)

Temperature (oC)

(b) 

0 200 400 600 800 1000

20

40

60

80

100

 PHA-10 (-OPh)

 PHA-11 (-Ph)

 PHA-12 (-OC2H5)

 PHA-13 (-OPh(Cl)2)

 PHA-14 (-OCH3)

Weight (%)

Temperature (oC)

(c) 

FIGURE 3-4. THE TGA CURVES OF PHA-1 AND ITS DERIVATIVES IN N2 (a) PHA-1 

AND HALOGENATED PHAs, (b) PHAs WITH METHOXY GROUPS, AND 

(c) PHAs WITH PHOSPHINATE OR PHOSPHATE GROUPS 

3-6
In PHA-7, hydroxyl groups are totally replaced by methoxy groups. PHA-7 is quite stable up to 

about 363°C, but then it has a sharp weight loss between 363°~469°C. The 40% weight loss in 

the first stage is apparently not due to the analogous PHA-to-PBO cyclization reaction in which 

17 wt% methanol would be released, but it is mainly due to the release of 1,3-dimethyl 

isophthalate from the polymer main chain. Copolymer PHA-8, with both methoxy and hydroxyl 

groups, shows three stages of decomposition. The first stage (240°~334°C) is due to the

cyclization of hydroxyl groups (6 wt% water loss as expected). The second stage (397°~476°C)

is related to the decomposition of the structures containing methoxy groups, and the third stage is 

the high-temperature decomposition of polymer backbone. The thermal stability of PHA-9 is 

very low due to the presence of large phosphate groups (-PO2(OMe)2). It begins to decompose

around 218°C. Although PHA-7, 8, and 9 have different side groups, they all show a similar 

decomposing stage between 600°~800°C, which is due to the decomposition of one particular 

structure. 

The thermal decomposition processes of PHA-10 to 14, which contains different phosphinate or 

phosphate groups, are very different from each other (figure 3-4(c)). PHA-10 and 11 have

relatively high thermal stability (300°C) due to their relatively strong bonds in phosphinate or

phosphate groups. However, PHA-12 to 14 start to lose weight around 180°C. It is believed that 

at low temperatures (180°~500°C), the main decomposition is the cleavage of phosphinate or 

phosphate side groups from the polymer main chain due to their relatively weak linkage and 

further decomposition of these phosphinates or phosphates. At high temperatures (above 

500°C), the polymer breaks along the main chain. Similar to PHA-1 and PHA-7 to 9, these 

phosphinate or phosphate PHAs all start a new decomposition step around 600°C, which

suggests that all these PHAs are converted into a similar structure that might contain some PBO 

rings before 600°C. 

In N2, all the PHAs can produce high char yields. Char can act as a thermal and mass transfer

barrier and greatly reduce the flammability of polymers. However, when PHAs are decomposed 

in air, the TGA curves are somewhat different (figure 3-5). Although oxygen has no effect on 

the first decomposition stage, it reduces the thermal stability of the second stage except for the 

PHAs with halogen groups (figure 3-5(b)). Above 600°C, all the PHAs except for those with 

phosphinate or phosphate groups (figure 3-5(c)) completely burn without leaving any char. It 

was concluded that oxygen does not affect the initial thermal stability, but that it can oxidize the 

carbonaceous char very easily at high temperatures. The presence of the halogen groups can 

improve the thermo-oxidative stability, while phosphate groups can preserve more char during 

burning. 

Besides the thermal stability and decomposition processes, another important thermal property

that can be obtained only by STA measurements is the enthalpy change associated with the 

weight loss. The high-temperature DSC curves of PHA and its derivatives are shown in

figure 3-6. 

3-7
0 200 400 600 800 1000

0

20

40

60

80

100

 PHA-1 (-OH)

 PHA-7 (-OMe)

(2)

(1)

Weight (%)

Temperature (oC)

(a) 

0 200 400 600 800 1000

0

20

40

60

80

100

 PHA-3 (m-Br)

 PHA-5 (m-Br, -CF3)

(2)

(1)

Weight (%)

Temperature (oC)

(b) 

0 200 400 600 800 1000

0

20

40

60

80

100

 PHA-9 (-OMe, -OPO(OMe)2)

 PHA-12 (-OPO(OC2H5)2)

(2)

(1)

Weight (%)

Temperature (oC)

(c) 

FIGURE 3-5. EFFECTS OF OXYGEN ON THE DECOMPOSITION OF PHA-1 AND 

ITS DERIVATIVES (a) PHA-1 AND ITS METHOXY DERIVATIVE,

(b) HALOGENATED PHAs, AND (c) PHOSPHATE PHAs, 

(1) IN N2 AND (2) IN AIR 

3-8
0 200 400 600 800

5

3

1

Exothermic

Temperature (oC)

(a)

0 200 400 600 800

9

8

7

Exothermic

Temperature (oC)

(b)

0 200 400 600 800

14

13

12

11

10

Exothermic

Temperature (oC)

(c)

FIGURE 3-6. HIGH-TEMPERATURE DSC CURVES OF PHA-1 AND ITS 

DERIVATIVES (a) PHA-1 AND HALOGENATED PHAs, (b) PHAs WITH 

METHOXY GROUPS, AND (c) PHAs WITH PHOSPHINATE 

OR PHOSPHATE GROUPS 

3-9
All the PHAs (except for PHA-10 and 11) show an endothermic peak in the early stage of 

decomposition, but they differ at high temperatures. In the cases of PHA-1, 3, and 5 

(figure 3-6(a)), the heat absorbed in the first stage is around 105~120 J/g as a consequence of the 

cyclization reaction and vaporization of water. In the second stage, PHA-1 shows a combination

of endo- and exothermic behavior, which might be due to the combined effects of decomposition

and char formation processes. PHA-3 and 5 instead show a distinct exothermic peak in the 

second stage, which might be due to the release of HBr and some cross-linking reactions. For 

PHA-7 with methoxy groups (figure 3-6(b)), the endothermic peak between 320°~395°C might

result from the melting of the polymer and some possible cyclization reactions. The exothermic 

peak that follows (396°~469°C) is probably due to a series of thermal decomposition reactions,

including the breaking of the polymer main chain. The heat events in phosphinate or phosphate 

PHAs (figure 3-6(c)) are more complicated. PHA-12 to 14 show endothermic peaks at low 

temperatures (180°~360°C) due to the release and decomposition of phosphinate or phosphate 

side groups. However, PHA-10 and 11 have a combination of endo- and exothermic peaks in the 

first stage (300°~430°C). The enthalpy change of methoxy, phosphinate, or phosphate PHAs is

difficult to determine at high temperatures. 

3.3.2 Flammability.

The PCFC results (table 3-2) show that PHA and most of its derivatives have rather low 

flammability compared to commercial polymers such as PE, PS, and PC. Fire resistance of

PHA-1 is close to polyimide. Moreover, bromine and trifluoromethyl groups can further reduce 

the flammability by releasing halogenated decomposition products with low flammability. As a 

result, PHA-5 is one of the few polymers that have extremely low flammability. The

flammability of PHA-7 is relatively high, but it can be reduced by partially replacing methoxy 

groups with hydroxyl (PHA-8) or phosphate groups (PHA-9) to form a copolymer, which can 

extend the decomposition temperature range and slow down the decomposition rate. 

However, if methoxy or hydroxyl groups are totally substituted by different phosphinate or

phosphate groups (PHA-10 to 14), the flammability of polymers is greatly dependent on the

types of substituents. PHA-10 and 11, which contain phenyl or phenoxy groups in the

phosphinate or phosphates, have relatively higher flammability. The higher flammability is due 

to their relatively faster decomposition rates and release of more flammable compounds such as 

benzene and phenol. The flammability of PHA-12 to 14 is greatly reduced due to the significant 

reduction in the mass loss rates. Therefore, the introduction of bulky phosphinate or phosphate 

side groups to a thermally stable PHA backbone does not always improve the flame resistance of 

the polymer even though the phosphinate or phosphate groups are widely used in the industry as 

flame-retardant additives for plastics. Worse, the flammability of the polymer might be 

increased due to fast cleavage of these bulky fuel-forming side groups. 

3-10
TABLE 3-2. FLAMMABILITY OF PHA AND ITS DERIVATIVES 

Polymers 

Heat Release 

Capacitya 

(J/g-K) 

Total 

Heata 

(kJ/g) 

Tmax

b 

(

o

C) 

Maximum Mass 

Loss Rate 

(x 103

 /s) 

Char 

Yield 

(%) 

PHA-7 130 17 409 1.4 43

PHA-1 42 10 633 0.4 56 

PHA-8 33 11 425 0.5 55 

PHA-9 18 9 658 0.2 60 

PHA-3 17 5 563 0.4 39

PHA-5 8 3 553 0.7 36 

PHA-10 340 15 327 3.3 36 

PHA-11 210 21 341 2.9 32 

PHA-12 73 9 304 0.4 41 

PHA-13 59 8 271 0.6 29 

PHA-14 19 8 319 0.2 52 

PE 1558 40 471 7.0 0

PS 1199 37 417 5.2 0

PC 382 19 514 3.3 17

Kevlar 292 15 576 2.5 32

PEEK 163 13 586 2.2 46

PI 29 9 602 0.5 50

a PCFC results. The rest are derivative of TGA results. 

b The temperature at maximum mass loss rate. 

Generally, PHAs with low mass loss rates usually have low heat release capacity (except for

halogenated PHAs). This is because there are generally two factors that can determine the heat

release capacity: maximum mass loss rate and the heat of combustion of the decomposition 

products at that temperature. For PHAs with similar backbone structures, the major 

decomposition products are not very different. Therefore, the mass loss rate becomes the most 

important factor that can determine the heat release rate. According to figure 3-7, PHA-1 and 

halogenated PHAs (PHA-3 and 5) decompose faster at high temperatures (maximum mass loss 

rates occur around 550°~650°C) due to the massive main-chain scission, while PHA-7, 8, and 

phosphinate or phosphate PHAs (PHA-10 to 14) have their maximum mass loss rates at low 

temperatures (around 300°~500°C) due to the fast cleavage of methyl, phosphinate, or phosphate 

groups. 

Although PHA-8 is the copolymer of PHA-1 and PHA-7, its flammability is almost the same as 

PHA-1 rather than an average of the two homopolymers. This nonlinearity means that 

copolymerization of two polymers with different thermal stability, thermal decomposition

process and flammability might be a good way to reduce flammability. The copolymerization 

can broaden the whole decomposition range and reduce the mass loss rate, therefore reducing the 

heat release rate. 

3-11
0 200 400 600 800 1000

0

1

2

3

4

5

6

 PHA-1 (-OH)

 PHA-3 (m-Br)

PHA-5 (m-Br, -CF3)

Temperature (oC)

Deriv. of weight (%/min)

(a) 

0 200 400 600 800 1000

0

2

4

6

8

10

 PHA-7 (-OMe)

 PHA-8 (-OMe, -OH)

 PHA-9 (-OMe, -OPO2(OMe)2)

Deriv. of weight (%/min)

Temperature (oC)

(b) 

0 200 400 600 800 1000

0

5

10

15

20

 PHA-10 (-OPh)

 PHA-11 (-Ph)

 PHA-12 (-OC2H5)

 PHA-13 (-OPh(Cl)2)

 PHA-14 (-OCH3)

Deriv. of weight (%/

min)

Temperature (oC)

(c) 

FIGURE 3-7. DERIVATIVE TGA CURVES OF PHA-1 AND ITS DERIVATIVES

(a) PHA-1 AND HALOGENATED PHAs, (b) PHAs WITH METHOXY GROUPS, 

AND (c) PHAs WITH PHOSPHINATE OR PHOSPHATE GROUPS

3-12
In conclusion, the major reasons for the low flammability of most PHA polymers are the stable

aromatic backbone structures, low mass loss rates, high char yields, and the ability to release 

flame-retardant molecules (such as water and halogenated compounds), which can act physically 

or chemically during combustion. However, the introduction of bulky, fuel-forming phosphinate 

or phosphate groups should be avoided in order to get good flame resistance. 

3.3.3 Characterization of Chars by IR and Elemental Analysis.

Chars are complex materials that contain fused aromatic structures and may include heteroatoms 

(O, N, P, and S). They are usually insoluble, which limits their characterization to the tools used

in solid-state chemistry and physics. The composition of the char is usually characterized by

elemental analysis. Table 3-3 lists some elemental analyses of PHA-1 pyrolyzed at different 

temperatures. 

TABLE 3-3. ELEMENTAL ANALYSES OF PHA-1 AND ITS CHARS AT 

DIFFERENT TEMPERATURES 

Measured 

(wt%) 

Calculated 

Temperature (wt%) 

(°C) C H N O C H N O

Residual 

Weight (%) 

25 (PHA) 67.26 3.78 7.56 21.4 69.4 4.1 8.1 18.4 100 

400 (PBO) 75.96 3.26 8.62 12.16 77.4 3.2 9 10.4 90

650 79.97 2.93 7.84 9.26 75

1000 87.07 0.44 3.78 8.71 50

According to table 3-3, the char of PHA-1 at 400°C has the same elemental composition as PBO, 

which supports the assumption that the first stage (250°~383°C) is due to the cyclization

reaction. With the temperature increasing, the contents of H, N, and O decrease dramatically, 

but the carbon content increases. At 1000°C, the formula of the char can be written as 

C27H1.63NO2, which suggests that the structure of the char at high temperatures must be some

fused aromatic and heteroaromatic rings with low hydrogen content. 

The IR spectra of PHA-1 chars produced at different temperatures are shown in figure 3-8. The 

tentative band assignments are given in table 3-4 [101]. According to the IR results, there is no 

difference between the spectra of room temperature and 250°C, which indicates that PHA-1 is 

stable until 250°C. When the polymer is heated to 350°C, the intensity of the broad absorption at

3294 cm-1 (O-H stretch) is greatly decreased because some of the hydroxyl groups have been 

converted into benzoxazole rings. In addition, most peaks in the region 2000 to 500 cm-1 either

shift or split into two peaks due to the ongoing cyclization reaction, which involves some

coexisting structures. Some new peaks also show up, such as the peaks at 1267, 1051, and 

705 cm-1 that are associated with the benzoxazole rings. At 400°C, the peaks at 3405 cm-1 (N-H 

stretch) and 3294 cm

-1 (O-H stretch) completely disappear, which suggests that the N-H and O-H 

groups have been totally changed into benzoxazole rings. The region near 1650-1500 cm-1 is 

very characteristic of benzoxazole. The C=C/C=N stretching vibrations (1624 cm-1) and the

peak at 1541 cm-1 are characteristics of the conjugation between the benzene and the oxazole 

rings. A broad peak at 1280-1231 cm-1 is due to the oxazole-ring breathing mode, and 

3-13
heterocyclic-ring vibration is found at 705 cm-1. The confirmation of PBO structure at 400°C by

IR further supports the proposition that the PHA undergoes cyclization reaction in the first 

decomposition stage. 

O

25oC 

υ C=O 

δN-H + υ C-N υO-H 

250o

C 

350oC 

υ N-H

υC-O-C 400o

C 

N

650oC υ C≡N 

υ N-H in --NH2 δAr-H

υ C=O 

FIGURE 3-8. INFRARED SPECTRA OF PHA-1 AT DIFFERENT TEMPERATURES 

TABLE 3-4. INFRARED BAND ASSIGNMENTS OF PHA AND PBO 

Wavenumber (cm-1) Tentative Assignment

3405 (m) Free non-hydrogen-bonded N-H stretching 

3294 (b) Self-associate O-H stretching 

3068 (sh) Aromatic C-H stretching 

1653 (s) C=O stretching 

1608(m), 1582(sh), 1409(m) Aromatic C-C stretching 

1518 (vs) N-H vibration and C-N stretching 

1230 (w) Aromatic C-O stretching 

863(m), 806(m) C-H out-of-plane bending in 1,2,4 three substituted benzene rings 

712 (m) C-H bending in 1,3 two substituted benzene rings 

1624 (m)* C=C/C=N stretching 

1541(s)* Ring vibration characteristics of conjugation between benzene 

and oxazole ring 

1460 (vs)* In plane ring vibration characteristic of two-substituted 

benzoxazole 

1282 (s), 1264 (s)* Oxazole ring breathing 

1073(m), 1049(m)* C-O-C stretching in benzoxazole ring 

*

Bands in PBO. All the peak positions refer to spectra collected at ambient temperature. s: strong; m: medium; w: 

weak; sh: shoulder; vs: very strong; b: broad.

3-14
When PHA-1 further decomposes at 650°C, the color of the film changes from amber to black. 

In the IR spectrum at 650°C, several features are apparent. New peaks at 3457, 3397 cm

-1

(apparently N-H stretch in NH2 groups), 2228 cm-1 (C≡N stretch in aromatic nitrile groups), and 

1685 cm-1 (carbonyl groups) can be easily identified. The peaks in the region from 1600 to 1200 

cm

-1 become broader and less resolved, but most of the aromatic bands are still present. In 

addition, the absorptions at 3061 cm-1 (aromatic C-H stretching) and 900-700 cm-1 (substituted

benzene ring vibration) become broader and stronger. All the results suggest that as the 

pyrolysis proceeds, the char becomes more and more aromatic in character and it contains some

CN, NH2 and CO functional groups. 

3.3.4 Identification of Volatiles by GC/MS.

The volatiles from all the PHAs are characterized by pyrolysis GC/MS to aid the development of 

decomposition mechanisms. The TIC pyrograms (pyrolysis GC/MS traces) of some PHAs are 

shown in figure 3-9. 

All the volatiles can be divided into four groups: (1) low boiling point products such as CO, 

CO2, H2O, CH3OH, and HCN, which cannot be separated effectively by normal GC operation 

and may come from the cyclization reaction or decomposition of the backbone; (2) aromatic 

hydrocarbons, amines, amides, nitriles, benzoxazoles, and isocyanates, which correspond to the 

partial fragments of polymer main chain; (3) Halogenated, methyl, phosphinate, and phosphate 

compounds, which are attributed to the cleavage of the substituents; (4) high boiling point

products formed by isomerization, rearrangement, or cross-linking reactions at high 

temperatures, such as 3,4-diphenyl-1H-pyrazole. 

About 70 wt% of volatiles ultimately released from PHAs (except for phosphinate or phosphate 

PHAs) are CO2, CO, H2O, and HCN, of which CO2 and CO are present in the largest quantities 

(around 50 wt%). In contrast, major decomposition products of PHA-10~14 consist of

phosphinates, phosphates, and their ester fragments such as phenol, benzene, 2,4-dichlorophenol, 

methanol, and ethanol. For the halogenated PHAs, bromine was observed in the volatiles not

only as HBr but also in the form of a small amount of brominated aromatic compounds (such as 

C6H4Br2 and C6H3Br3). However, fluorine was only detected as fluorinated compounds (such as

CF3Br and CF3CH2Br). All these halogenated products have low flammability on their own and 

are very good gas-phase flame-retardants during combustion. 

An important characteristic of the decomposition of PHAs with methoxy groups is that their 

decomposition products contain significant amounts of methyl- or methoxy-substituted aromatic 

compounds. The methyl or methoxy groups might come from the cleavage of side groups. 

It was also found that HCN (about 5~10 wt%) is only produced at high temperatures from these 

polymers, usually above 500°C. With temperature increase, the CO/CO2 ratio increases. 

3-15
 

H2O, CO2 

CO, HCN 

CN

NC CN C O

N

NH N

(a) (b) H2O, CO2 

CO, HCN

CN

C O

B r B r N

HBr 

 

H2O , CO2 , CO, 

HCN, CF3Br, 

CF3CH2Br

CO2, CO 

H2O, HCN 

CH3OH 

CN

C O

N

MeOOC COOH

MeOOC COOMe

NC CN

(d)

(c) 

 

H2O CO2 

CO HCN 

CN

P

O

PhO OPh

OPh

P

O

Ph Ph

OPh

OH

(e) P

O

C2H5O O C2H5

O C2H5 (f)

H2O CO2, CO 

HCN,C2H5OH,

CH2=CH2

FIGURE 3-9. PYROLYSIS GC/MS TRACES OF PHA-1 AND ITS DERIVATIVES 

(HEATING TO 930°C AT 4.3°C/s) (a) PHA-1, (b) PHA-3, (c) PHA-5, 

(d) PHA-7, (e) PHA-10, AND (f) PHA-12 

3-16
The thermal decomposition products at different temperature ranges are also studied. For PHAs 

containing only hydroxy groups (PHA-1 (figure 3-10), PHA-3 and 5), the main decomposition

products during the first stage are water and a small amount of CO2, which suggests some

hydrolytic decomposition. The water generated during cyclization could be responsible for this 

hydrolysis. When these polymers are heated to higher temperatures, they release some aromatic 

compounds, such as the heterocyclic-aromatic species 2-phenyl benzoxazole, which is a typical 

structure within PBO. However, the major volatiles are still CO2, CO, H2O, and HCN, which

along with high char yields are responsible for their low flammability. 

(a)

H2O (>90 wt%), CO2 (<10 wt%)

CN

NC CN

C

O

N

NH N

(b) 

CO2, CO, HCN

FIGURE 3-10. PYROLYSIS GC/MS TRACES OF PHA-1 AT DIFFERENT TEMPERATURE 

RANGES (HEATING RATE, 4.3°C/s) (a) 250° ~ 383°C AND (b) 383° ~ 930°C 

In contrast, for PHAs with methoxy groups (PHA-7 (figure 3-11) to 9), the decomposition 

products at low temperatures not only contain CO2, CO, H2O, and CH3OH but also a large 

amount of 1,3-dimethyl isophthalate. At higher temperatures, these polymers give out more 

aromatic compounds with methoxy or methyl substituents. 

3-17
(a) MeOOC COOMe

CO2, CO 

H2O, CH3OH 

MeOOC COOMe

CN

C

O

N

MeOOC COOH

NC CN

CO2, CO, HCN,

H2O, CH3OH 

(b) 

FIGURE 3-11. PYROLYSIS GC/MS TRACES OF PHA-7 AT DIFFERENT TEMPERATURE 

RANGES (HEATING RATE, 4.3°C/s) (a) 350° ~ 469°C AND (b) 469° ~ 930°C 

The major decomposition products of phosphinate or phosphate PHAs below 500°C 

(figure 3-12) are flammable phosphinates and phosphates as well as their ester fragments, which 

lead to their high flammability. At high temperatures, some aromatic compounds from the 

polymer backbone are released. 

3-18
(a) OH

P

O

PhO OPh

OPh

P

O

Ph Ph

OPh

H2O CO2 

CO HCN 

OH

CN

NC CN

COOH

(b)

FIGURE 3-12. PYROLYSIS GC/MS TRACES OF PHA-10 AT DIFFERENT 

TEMPERATURE RANGES (HEATING RATE, 4.3°C/s) 

(a) 250° ~ 500°C AND (b) 500° ~ 930°C 

In summary, at low temperatures (below 500°C), most volatiles released are CO2, H2O, CH3OH,

phosphinate, phosphates, and their ester fragments, depending on the structures of the PHAs. At

high temperatures (above 500°C), PHAs produce more aromatic volatiles resulted from

backbone scission. 

3.3.5 Thermal Decomposition Mechanisms.

Thermal decomposition mechanisms of PHA-1 and its derivatives were proposed by 

identification of the major volatiles. The cyclization of PHA-1 into PBO is well known [82-84]. 

Pearce, et al. have also studied the basic mechanisms for the formation of PBOs from ortho 

halogen-, nitro-, and cyano-substituted polyamides [93-98]. They found that the char yield and 

3-19
flame resistance of these polyamides can all be greatly improved due to the ring-forming reaction 

during their pyrolysis. However, there is no detailed research on the thermal decomposition of

methoxy and phosphinate or phosphate PHAs. 

Possibly, PHA derivatives might decompose by the same mechanism as PHA-1, shown in 

figure 3-13. First, they are cyclized to PBO by releasing some small molecules (ROH). The 

PBO structures then break down at high temperatures. In the following discussion, it will be 

shown whether this mechanism is valid to all the PHA derivatives. 

C PHAs

O

C

O

R2 R2

R1

RO

NH

OR

NH

PBOs

O

N N

O

R2 R2

R1

ROH

Cyclization ?

+

(H2O, CH3OH, phosphinate or phosphates)

R = H, CH3, PO(OPh)2, POPh2, PO(OMe)2, PO(OC2H5)2, PO(OPhCl2)2

 R1 = - or C(CF3)2

 R2 = H or Br

FIGURE 3-13. PRESUMED CYCLIZATION OF PHA AND ITS DERIVATIVES 

Based on the GC/MS trace of PHA-1 at low temperatures, water is the major volatile, which

comes from intramolecular cyclization. In addition, H2O could also be generated by the 

intermolecular condensation of iminol forms [94] (figure 3-14). However, this reaction has a 

lower probability of occurring because the presence of 2-phenyl benzoxazole in the hightemperature decomposition volatiles strongly suggests that H2O is formed by intramolecular 

cyclization (figure 3-15(a)(I)). 

C

O

N

H

C N

OH C N

O

C N

+ H2O

FIGURE 3-14. WATER GENERATED BY INTERMOLECULAR REACTION 

3-20
FIGURE 3-15. PROPOSED THERMAL DECOMPOSITION MECHANISMS OF PHAs 

3-21
A small amount of CO2 is detected in the first decomposition stage of PHA-1. This might be due 

to the hydrolytic cleavage of the amide linkage, which can lead to the formation of two 

fragments with NH2 and COOH end-groups. The COOH groups would then decarboxylate to

give out CO2. This hydrolytic reaction is quite possible because a significant amount of H2O is

present in this stage. 

The second stage is the decomposition of the PBO structure formed. High-temperature thermal 

decomposition might be initiated by random homolytic cleavage of the strong phenyl-phenyl 

bond in the main chain, followed by hydrogen transfer, rearrangement, cross-linking, and other 

secondary reactions. Decomposition products from the second stage include five major aromatic 

compounds: benzene, benzonitrile, benzenedicarbonitrile, 2-phenyl benzoxazole, and 3,4-

diphenyl-1H-pyrazole (figure 3-10). PHA-3 and 5 decompose in almost the same way as PHA1, but the amount of aromatic volatile is greatly reduced by the introduction of heavy bromine 

atom (figure 3-9(b)). HBr is formed above 400°C by homolytic cleavage of the aromatic C-Br 

bond, followed by hydrogen abstraction. 

Although the only structural difference between PHA-7 and PHA-1 is OCH3 versus OH side 

groups, their decomposition mechanisms are very different. The detection of 2-phenyl 

benzoxazole from PHA-7 at high temperatures indicates that some cyclization reactions also

occurred in the first decomposition stage. However, if PHA-7 is cyclized according to the same

mechanism proposed for PHA-1, about 17 wt% methanol should be released. However, only 1.5 

wt% methanol is detected by pyrolysis GC/MS, and the 40% weight loss in the first stage is due

to other compounds such as CO2, CO, H2O, and dimethyl isophthalate (figure 3-11). The 

formation of dimethyl isophthalate can only be done by breaking the polymer main chain. 

Therefore, it is believed that both cyclization and main-chain scission occurred in PHA-7 during 

the first decomposition stage (figure 3-15(a)(II)). In addition, the cyclization reaction does not 

proceed by releasing methanol, but more likely through another route that releases water 

(approximately 5 wt% detected by pyrolysis GC/MS). Then, at the end of the first stage, PHA-7 

is converted into a structure with both benzoxazole rings and methoxy groups. Because both 

PHA-1 and 7 have the same backbone structures, the difference in decomposition mechanisms

must be attributed to the side groups. The O-Me bond (50 kcal/mol), the weakest bond in PHA7, is much weaker than O-H bonds (72 kcal/mol) in PHA-1. As a result, the methyl groups can 

be cleaved easily from the polymer backbone and react with the other aromatic radicals to form 

various methyl- or methoxy-substituted compounds. The decomposition mechanism of the

copolymer PHA-8 appears to be a combination of that for PHA-7 and 1. 

Similarly, the bulky phosphinate or phosphate side groups in PHA-10~14 can be easily cleaved 

from the polymer backbone at low temperatures (figure 3-15(a)(III)). Then following the same

route as PHA-7, the polymers can be partially cyclized. Therefore, before any main-chain 

scission (above 500°C), the polymers are transformed into a structure with both benzoxazole 

rings and phosphinate or phosphate groups. According to elemental analysis, the char at 930°C 

still contains a certain amount of phosphorus, which might be trapped by some cross-linking 

reactions during decomposition (figure 3-15(a)(III)). This observation also proves that 

phosphorous can reduce flammability by promoting the char formation. 

3-22
The methoxy and phosphate PHA-9 is a copolymer of PHA-7 and 14. At low temperatures 

(below 500°C), this polymer breaks at both side-chain and main-chain positions to give out 

trimethyl phosphate and dimethyl isophthalate. 

At high temperatures (above 500°C), the decomposition of methoxy and phosphinate or 

phosphate PHAs is basically due to the random main-chain scission of a general structure that 

contains both benzoxazole rings and methoxy, phosphinate, or phosphate groups 

(figure 3-15(b)). For PHA and halogenated PHAs, they have been totally converted into quasiPBO structures at the end of the first stage. Many reactions can occur at high temperatures, such 

as main-chain scission to give out different aromatic volatiles and recombination and

aromatization to form char. 

The thermal decomposition mechanisms of all the PHAs are summarized in figure 3-15. 

3.4 DISCUSSION.

PHA and most of its derivatives have very low flammability, especially the ones containing 

halogen groups. PHA-7 with methoxy groups is more thermally stable, but it exhibits higher 

flammability due to the main-chain scission at low temperatures. PHA-10 and 11 are also

relatively flammable due to the extensive cleavage of fuel-forming phosphinate or phosphate 

groups. The thermal decomposition process of the PHAs can be roughly divided into two stages.

In the first stage (below 500°C), small molecules such as water, methanol, and phosphinates or 

phosphates, as well as their ester fragments, are released to form some quasi-PBO structures. In 

the second stage (above 500°C), the random scission of the polymer backbone will occur. Most

PHAs show an endothermic peak at low temperatures, but due to different mechanisms such as

cyclization, melting, and decomposition. Halogenated PHA-3 and 5 show a distinct exothermic 

peak at high temperatures due to the formation of HBr and some cross-linking reactions. IR and 

elemental analysis all prove that the first decomposition stage of PHA-1 corresponds to 

cyclization into PBO. The major decomposition products of most PHAs (except for phosphinate 

or phosphate PHAs) are CO, CO2, H2O, HCN, and a small amount of aromatic compounds. The 

low-flammable volatiles, low mass loss rates, and high char yields are the major reasons for their 

low flammability. Different from the complete cyclization of PHA and halogenated PHAs, 

methoxy-, phosphinate- or phosphate-substituted PHAs can only partially cyclize into PBO

structures. 

3-23/3-24
4. FIRE-RESISTANT, UV/VISIBLE-SENSITIVE POLYARYLATES, COPOLYMERS, AND

BLENDS.

4.1 INTRODUCTION. 

Polyarylates, a group of aromatic polyesters of phthalic acid and bisphenols, represent a very 

important family of engineering thermoplastics with enhanced long-term resistance to elevated 

temperature in advanced applications. They have many good properties, such as high modulus, 

flexural recovery, high heat deflection temperature, low notch sensitivity, and good electrical 

properties. Most of all, these materials show a high resistance to ignition and flame spreading 

without additives [6]. 

Varying the structures of phthalic acids and bisphenols, a series of polyarylates have been 

synthesized. Among them, polyarylates based on chloral and its derivatives have been found to 

be extremely fire resistant [102]. Especially, polyarylates based on BPC II have received 

considerable interest due to their good solubility, mechanical, dielectrical, optical, and excellent 

heat- and flame-resistant properties [103-105]. Brzozowski was one of the first to use BPC-II in 

the synthesis of polycarbonates and polyarylates through interfacial polycondensation [106-108]. 

It was found that these polymers are the least combustible and fuming of all existing

thermoplastics. Recently, ultraviolet (UV)/visible-sensitive polyarylates with improved thermal 

and chemical stability have become Brzozowski’s major research interests [109-112]. Chalcon 

II (4, 4'-dihydroxy-3-ethoxy-benzylidenoacetophenone )-polyarylate is of particular importance

due to its high UV-sensitivity, economic (high yield), and ecological (nontoxic) advantages [111 

and 113]. Its copolymers with bisphenol A (BPA) or BPC II monomer meet the main 

requirements for photo-resists (e.g., high UV sensitivity, high chemical resistance, high 

adhesion, high tenacity, and good solubility in harmless solvents). In addition, the images have a 

very good resolution and contrast and can be easily developed. Therefore, these polyarylates are 

potentially useful in the photolithography process and some other photopolymer applications 

[111]. 

Although it is important to develop new fire-resistant polymers, the simplest way to control

flammability from a commercial standpoint is to modify the structure and composition of

existing polymers by either copolymerization or polymer blending. This can minimize the 

effects of small molecule, flame-retardant additives on the processing and performance of the 

host polymers and avert outward diffusion in the system and the consequent risk of 

environmental contamination. On the other hand, some other properties of the host polymers 

might also be improved by incorporation of another component. However, two important issues 

must be considered when blending. One is the compatibility between polymers. The other is the 

cost efficiency of blending a small amount of a very flame-retardant, high-charring polymer with 

a large amount of very flammable, low-charring polymer. Until now, little has been done in the

field of flammability-composition relations except for some studies on BPA- and BPC IIpolycarbonates [114 and 61]. 

In this section, the thermal decomposition behavior and flammability of three polyarylates based 

on BPA, BPC II, Chalcon II, and their copolymers and blends were fully characterized. The 

relationships between flammability and chemical structure/composition of these polyarylates

have also been investigated. 

4-1
4.2 EXPERIMENTAL.

4.2.1 Materials. 

Homopolyarylates based on BPA, BPC II, and Chalcon II (figure 4-1) as well as corresponding 

copolymers were provided by Prof. Brzozowski, Warsaw University of Technology. Polymer

blends were made by mixing different polymers with varied weight ratios in methylene chloride, 

then solution-casting into films. 

O R O C

O

C

O

n R1

R R1

BPA C(CH3)2 H

BPC II C(=CCl2) H

Chalcon II CH=CHC(O) OC2H5

FIGURE 4-1. STRUCTURES OF BPA-, CHALCON II-, AND BPC II-POLYARYLATES 

The polymers used for blending are polysulfone (-O-Ph-C(CH3)2-Ph-O-Ph-SO2-Ph-) supplied by 

BP Amoco Co.; polystyrene (Mp=514,000) obtained from Polymer Laboratories; and 

poly(ethylene oxide) (Mn = 600,000) purchased from Aldrich. 

4.2.2 Characterization.

DSC measurements were carried out on a DuPont 2910 instrument. The heating rate was 

10°C/min. The experimental conditions for TGA, STA, pyrolysis GC/MS, and PCFC 

measurements were the same as those described in section 2.3. 

UV/visible spectra were recorded by using a UV/visible spectrophotometer (Hewlett-Packard 

8453). 

The cured samples used for TGA and PCFC analyses were prepared under an OAI 500W deepUV lamp with intensity of 10 mW/cm2

. 

4.3 RESULTS.

4.3.1 Flammability and Thermal Decomposition of BPA-Polyarylates. 

Three kinds of phase transfer catalysts—cetyltrimethylammonium bromide (CTMA Br), crown 

ether (18-crown-6), and dimethyl sulfoxide (DMSO)—were used to optimize the interfacial

polymerization conditions of BPA-polyarylate [115]. It has been found that the polymers

obtained by using 18-crown-6 and DMSO have higher molecular weight, thus, higher glass

transition temperature (Tg) and higher thermal stability. However, the increase of molecular

weight has no significant effect on the flammability of BPA-polyarylate due to its randomscission decomposition mechanism (table 4-1). 

4-2
TABLE 4-1. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

BPA-POLYARYLATES

Catalysts 

H.R. Capacity 

(J/g-K) 

Total Heat Released

(kJ/g) 

Char Yield

(%) 

T95%a 

(°C) 

Tg

b 

(°C) 

CTMA Br 360 18 27 431 155 

DMSO 380 19 27 463 166

18-crown-6 400 19 26 458 174

a

Temperature at 5% weight loss from TGA 

b

Glass transition temperature from DSC 

4.3.2 Thermal Decomposition and Flammability of Homopolyarylates.

Thermal decomposition processes of BPA-, Chalcon II-, and BPC II-homopolyarylates are 

shown in figure 4-2. It can be seen that all the polymers decompose in a single step. They all 

have a relatively high thermal stability and will not start to lose weight dramatically until 370°C. 

However, the bridging groups and side groups in the bisphenols do have some effects on the heat

resistance of polyarylates. The introduction of 1,1-dichloroethylene groups (BPC II) leads to an

obvious drop (40°C) in thermal stability when compared to BPA-polyarylate. The thermal 

stability of Chalcon II-polyarylate is also greatly reduced due to the presence of bulky ethoxy 

side groups. The order of the thermal stability of these homopolyarylates is BPA > BPC II > 

Chalcon II. The derivative of TGA curves (DTG curves) shows that the mass loss rate of BPC 

II- and Chalcon II-polyarylates are significantly lower than BPA-polyarylate, which indicates

that BPC II- and Chalcon II-polyarylates decompose much slower. Moreover, these two 

polymers can produce more char at high temperatures (above 40%) due to the cross-linking of 

double bonds. 

0 200 400 600 800 1000

0

20

40

60

80

100

Temperature (oC)

Weight (%)

0

10

20

30

40

Deriv. Weight (%/min)

 BPA

 Chalcon II

 BPC II

FIGURE 4-2. THE TGA AND DTG CURVES OF BPA-, CHALCON II-, AND 

BPC II-POLYARYLATES 

The high-temperature DSC curves are shown in figure 4-3. It can be seen that all the polymers 

are amorphous, with Tgs around 140°~150°C and onset decomposition temperatures around 

4-3
400°C (table 4-2). The large temperature window between softening and thermal decomposition

allows processing by injection and extrusion molding. During decomposition, BPA- and 

Chalcon II-polyarylates show an endothermic peak, but BPC II-polyarylate decomposes 

exothermically, which may be due to the formation of HCl or some cross-linking reactions. 

100 200 300 400 500 600 700 800

BPA

Chalcon II

BPC II

Exothermic

Temperature (oC)

FIGURE 4-3. HIGH-TEMPERATURE DSC CURVES OF BPA-, CHALCON II-, AND 

BPC II-POLYARYLATES 

TABLE 4-2. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

HOMOPOLYARYLATES 

Polymer 

H.R. 

Capacity 

(J/g-K) 

Total 

Heat 

(kJ/g) 

Char 

Yield 

(%) 

Tmax

a 

(°C) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tg 

b

(°C) 

T95%c

(°C) 

∆Hd

(J/g) 

BPA 360 18 27 488 2.2 155 431 168

Chalcon II 110 10 41 425 0.9 136 389 203 

BPC II 12 4 51 472 0.6 151 407 302 e

a Temperature at maximum mass loss rate from DTG curves

b Glass transition temperature from DSC c

 Temperature at 5% weight loss 

d Heat of decomposition measured from STA e Exothermic decomposition peak 

Table 4-2 shows the PCFC results as well as some TGA results, which show that different

bridging groups in bisphenols also have a big influence on the flammability of polymers. 

Generally, the flammability of polymers is determined by many factors, of which, rate of

decomposition (mass loss rate) and the amount and flammability of volatiles produced are the 

most important. The introduction of cross-linking groups (double bond in Chalcon II and 

BPC II) can greatly enhance the formation of char and therefore reduce the amount of fuel

generated. It was found that the BPC II unit (1,1’-diphenyl-ethylenedichloride) is the major 

structure responsible for the char-forming process [116-118]. On the other hand, according to 

the pyrolysis GC/MS analyses (figure 4-4), the major decomposition products of BPA- and 

4-4
Chalcon II-polyarylates are a series of phenols and some other flammable aromatic compounds. 

BPC II-polyarylate releases a lower amount of flammable compounds but more CO2, CO, HCl, 

and some chlorinated aromatic compounds that have relatively low fuel values and may also 

confer flame-retardant effects in the gas phase. Therefore, the reduced heat release capacity and 

total heat of combustion of Chalcon II-polyarylate (compared with BPA-polyarylate) is mainly 

due to a lower mass loss rate and less fuel generated. While in the case of BPC II-polyarylate,

release of less flammable decomposition products is another important factor for its low 

flammability. In all, compared with some other commercial polymers, Chalcon II-, and BPC IIpolyarylates are more heat and flame resistant, and BPC II-polyarylate has especially low 

flammability. 

(a) 

OH

OH

OH

OH

OH

C O

O

OH

C2H5 O

O

CO2,CO 

CH4

OH

COOH

OH

OH

OC2H5

C C

O

OCH3

O

HO

CO2,CO 

C2H6

(b) 

(c) 

CO2, CO, HCl

Cl

OH

COCl

COOH

O

C C

O

OCH3

O

HO

FIGURE 4-4. PYROLYSIS GC/MS TRACES OF BPA-, CHALCON II-, AND BPC IIPOLYARYLATES (TEMPERATURE RANGE: 250° ~ 930°C, HEATING RATE: 4.3°C/s) 

(a) BPA-POLYARYLATE, (b) CHALCON II-POLYARYLATE, AND 

(c) BPC II-POLYARYLATE 

4-5
4.3.3 UV/Visible-Sensitive Chalcon II-Polyarylate.

Chalcon II-polyarylate is a UV/visible-sensitive polymer containing CH=CHC(O) groups. The

UV spectra of Chalcon II-homopolymer and copolymers are shown in figure 4-5. 

300 400 500 600

0.0

0.2

0.4

0.6

0.8

1.0 Chalcon II

 BPC II

 BPA

Absorbance (AU)

Wavelength (nm)

(a) 

300 400 500 600

0.0

0.2

0.4

0.6

0.8

1.0 Chalcon II

 67% Chalcon II

 33% Chalcon II

 BPA

Absorbance (AU)

Wavelength (nm)

(b) 

FIGURE 4-5. ULTRAVIOLET SPECTRA OF POLYARYLATES CONTAINING CHALCON 

II-MONOMER (a) HOMOPOLYMERS AND (b) BPA-CHALCON II COPOLYMERS

According to figure 4-5, besides the peak at 238 nm that can be attributed to the absorption of

phenyl ring, there is another broad absorption between 300~400 nm which is due to the 

-CH=CHC(O)- structure. For the copolymers, with the increased content of Chalcon II 

monomer, the intensity of this absorption increases accordingly. 

It had been reported that some UV-sensitive polyarylates with a similar structure can form photocross-linking after UV exposure [119]. In these studies, in order to know whether photo-crosslinking has an effect on the thermal decomposition and flammability of these polymers, Chalcon

II-polyarylate was exposed to UV or visible light for various amount of time. It was found that 

Chalcon II polymer is no longer soluble in methylene chloride after exposure, which suggests the 

formation of photo-cross-links (figure 4-6). 

4-6
O

C2H5O

C

O

O C

O

O

C2H5O

C

O

O C

O

O

C2H5O

C

O

O C

O

O

C2H5O

C

O

O C

+ O

C UV-Vis

C

O

O

C

C

O

O

FIGURE 4-6. PHOTO-CROSS-LINKING OF CHALCON II-POLYARYLATE 

TGA results show that the thermal stability of the cured polymers has decreased. They start to 

decompose around 200°~250°C and then merge into the same major decomposition step after

about 6% weight loss (figure 4-7). The decrease in thermal stability is apparently due to the 

disruption of the conjugated system and the formation of weak linkages around cross-linking 

points (figure 4-6). 

0 200 400 600 800 1000

30

40

50

60

70

80

90

100

 0 min

 1.5 min

 4 min

Weight (%)

Temperature (oC)

(a) 

0 200 400

90

92

94

96

98

100

 0 min

 1 min

 1.5 min

 2 min

 4 min

 24hrs (visible light)

Weight (

%)

Temperature (oC)

(b) 

FIGURE 4-7. THERMAL DECOMPOSITION OF CHALCON II-POLYARYLATE AFTER 

UV/VISIBLE-EXPOSURE (a) FULL TGA CURVES AND (b) INITIAL DECOMPOSITION 

4-7
4-8

It was also found that the TGA curves of polymers cured for more than 4 minutes almost overlap 

each other, which means the photo-curing process is completed after 4 minutes. This conclusion 

is confirmed by other studies [111 and 112] that also show that the mechanical properties of the 

polymers can be greatly improved by curing. However, the flammability measured by the PCFC 

method shows no difference between cured and noncured samples, except that cured samples 

have slightly higher char yields. 

4.3.4 Thermal Decomposition and Flammability of Copolymers and Terpolymers. 

Thermal decomposition and flammability of three series of copolymers (BPA-Chalcon II, BPABPC II, and BPC II-Chalcon II) and BPA-Chalcon II-BPC II terpolymers were investigated. The 

results are shown in figures 4-8 and 4-9 and in table 4-3. 

0 200 400 600 800 1000

40

50

60

70

80

90

100

Chalcon II:BPC II

 1:0

 2:1

 1:2

 0:1

Weight (%)

Temperature (oC)

100 200 300 400 500 600 700 800

1:0

2:1

1:2

0:1

Chalcon II : BPC II

Exo up

Temperature (

o

C)

FIGURE 4-8. THERMAL DECOMPOSITION OF CHALCON II-BPC II COPOLYMERS 

(THE NUMBERS ARE MOLAR RATIOS) (a) TGA AND (b) DSC 

(a) 

(b) 
0 200 400 600 800 1000

20

40

60

80

100 BPA:Chalcon II:BPC II

 4:1:1

 1:4:1

 1:1:1

 1:1:4

Weight (%)

Temperature (oC)

(a)

100 200 300 400 500 600 700 800

BPA:Chalcon II:BPC II

4:1:1

1:4:1

1:1:1

1:1:4

Exo up

Temperature (oC)

(b) 

FIGURE 4-9. THERMAL DECOMPOSITION OF BPA-CHALCON II-BPC II 

TERPOLYMERS (THE NUMBERS ARE MOLAR RATIOS) (a) TGA AND (b) DSC 

It can be seen that the thermal decomposition and flammability of copolymers and terpolymers 

change systematically with composition. With an increased fraction of flame-retardant, highcharring units such as Chalcon II or BPC II, the heat release rate and the total heat released are

reduced, and the char yield increases correspondingly (table 4-3). 

At a very high concentration of BPC II monomer (67 mol%), the flammability of the copolymers 

and terpolymers is completely determined by the amount of BPC II units and independent of the

structure of the other components (figure 4-10), which indicates that BPC II is an efficient flameretardant unit. In addition, the heat involved in the decomposition process changes from 

endothermic to exothermic with the increased molar fraction of BPC II units. 

4-9
TABLE 4-3. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

CO- AND TERPOLYMERS 

Composition 

(Molar Ratio) 

H.R. 

Capacity 

(J/g-K) 

Total 

Heat 

(kJ/g) 

Char 

(%) 

Tmax

(°C) 

Max. Mass 

Loss Rate 

(x103

/s) 

T95% 

(°C) 

BPA : Chalcon II 

2:1 140 16 33 489 1.1 408

1:2 120 14 35 426 0.8 369

BPA : BPC II 

2:1 110 12 40 501 1.2 426

1:2 30 7 50 521 0.5 413

Chalcon II : BPC II 

2:1 76 9 40 425 0.7 398

1:2 30 7 48 428 0.4 390

BPA : Chalcon II : 

BPC II 

4:1:1 143 14 38 498 1.3 417

1:4:1 83 12 42 431 0.6 389

1:1:1 54 11 46 504 0.7 409

1:1:4 29 8 49 523 0.5 390

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.00

0.25

0.50

0.75

1.00

mol% BPC II mol% Chalcon II

mol% BPA

0.67

0.33 0.67

0.33

0.33 0.67

Chalcon II

BPA

BPC II

(29,8) (143,14)

(83,12)

(76,9)

(30,7)

(12,4)

(110,12) (30,7)

(110,10)

(120,14)

(140,16) (54,11)

(360,18)

FIGURE 4-10. TERNARY PLOT OF FLAMMABILITY OF COPOLYMERS 

AND TERPOLYMERS

(The numbers in the parentheses are heat release capacity (J/g-K) and total heat (kJ/g).)

4-10
After careful investigation of the relationship between flammability and composition

(figure 4-11), the total heat released was found, usually, to change linearly with the composition.

However, the change of heat release capacity depends on the chemical structure of the 

components. For BPA-BPC II and BPA-Chalcon II copolymers, there is an obvious synergistic 

effect. That means by adding only a very small amount of a low-flammable component, the

flammability of polymers can be dramatically reduced. However, the flammability of Chalcon 

II-BPC II copolymer almost changes linearly with composition. 

0 20 40 60 80 100

0

100

200

300

400

(3)

(2)

(1)

Heat release capacity (J/g.K)

wt% low-flammable component in copolymers

(chalcon II or BPC II)

(a) 

0 20 40 60 80 100

0

5

10

15

20

25

(3) (2)

(1)

Total heat released (kJ/g)

wt% low-flammable component in copolymers

 (Chalcon II or BPC II)

(b) 

FIGURE 4-11. COMPOSITION AND FLAMMABILITY RELATIONSHIP OF 

COPOLYMERS (a) HEAT RELEASE CAPACITY, (b) TOTAL HEAT RELEASED, (1) BPACHALCON II, (2) BPA-BPC II, AND (3) CHALCON II-BPC II 

4-11
4.3.5 Thermal Decomposition and Flammability of Blends.

Four kinds of blends were studied, all of which include BPC II-polyarylate as the flame-retardant 

component. The selection of the other polymer (polysulfone (PSF), BPA-polyarylate, PS, and 

PEO) is based on the structure of the polymer and whether this polymer is charring on 

decomposition. Several interesting phenomena were observed regarding thermal stability and 

flammability. It was found that the thermal stability, decomposition process, and char yield of

PSF/BPC II-polyarylate blends change systematically with composition (figure 4-12), and the 

trend of change is similar to BPA-/BPC II-polyarylate blends [119]. That is, with the increased 

amount of BPC II-polyarylate, the thermal stability and char yield of the blends gradually shift to

the direction of pure BPC II-polyarylate. 

0 200 400 600 800 1000

20

40

60

80

100

wt% BPC II-polyarylate

 0%

 25%

 50%

 75%

 100%

Weight (%)

Temperature (oC) 

(a) 

0 100 200 300 400 500 600 700 800

20

40

60

80

100

wt% BPC II-polyarylate

 0%

 25%

 50%

 75%

 100%

Weight (%)

Temperature (oC)

(b) 

FIGURE 4-12. THE TGA CURVES OF PSF (BPA-)/BPC II-POLYARYLATE BLENDS 

(a) PSF/BPC II-POLYARYLATE AND (b) BPA-/BPC II-POLYARYLATE [119] 

4-12
However, blends containing PS or PEO behave completely different during decomposition 

(figure 4-13). The onset decomposition temperatures of PS/BPC II-polyarylate blends are all the 

same (approximately 370°C, just between the two homopolymers) regardless of the composition,

while all PEO/BPC II-polyarylate blends start to decompose at the same temperature as PEO 

homopolymer. 

0 200 400 600 800 1000

0

20

40

60

80

100

0% (PS)

25%

50%

75%

100%

wt% BPC II-polyarylate

Weight (%)

Temperature (oC)

(a) 

0 200 400 600 800 1000

0

20

40

60

80

100

100%

75%

50%

25%

0% (PEO)

wt% BPC-II polyarylate

Weight (%)

Temperature (

o

C)

(b) 

FIGURE 4-13. THE TGA CURVES OF PS (PEO) /BPC II-POLYARYLATE BLENDS 

(a) PS/BPC II-POLYARYLATE AND (b) PEO/BPC II-POLYARYLATE 

Similar to copolymers, the total heat of combustion of blends changes linearly with composition,

but the change of heat release capacity and char yield is nonlinear with composition 

(figure 4-14). 

4-13
0 20 40 60 80 100

0

200

400

600

800

1000

1200

(4)

(3)

(2)

(1)

Heat release capacity (J/g.K)

wt% BPC II-polyarylate

(a) 

0 20 40 60 80 100

0

5

10

15

20

25

30

35

40

(4)

(3)

(2)

(1)

Total heat released (kJ/g)

wt% BPC II-polyarylate

(b) 

0 20 40 60 80 100

0

10

20

30

40

50

60

(2)

(1)

(3)

(4)

Char yield (%)

wt% BPC II-polyarylate

(c) 

FIGURE 4-14. STRUCTURE-COMPOSITION-FLAMMABILITY OF BLENDS 

CONTAINING BPC II-POLYARYLATE (a) HEAT RELEASE CAPACITY, 

(b) TOTAL HEAT RELEASED, (c) CHAR YIELD, (1) PS, (2) PEO, 

(3) BPA-POLYARYLATE, AND (4) PSF 

4-14
For the blends containing PSF or BPA-polyarylate, the heat release capacity and char yield 

change synergistically with composition. However, for PS or PEO, they change almost linearly. 

This is because PS (or PEO) and BPC II-polyarylate are largely phase separated in the blends

due to their distinctive structure differences. Therefore, there is no interaction between these two 

components during decomposition. However, PSF and BPA-polyarylate have similar aromatic 

structures to BPC II-polyarylate, and they all can form a certain amount of char on their own. 

These properties can lead to some kind of intermolecular interaction between two components, 

which can favor char formation and further slow down the decomposition process. In all, the

decrease in the heat release rate of blends is mainly attributed to the wider decomposition

temperature range and, therefore, lower mass loss rate. 

4.4 DISCUSSION.

BPC II-polyarylate is an extremely heat- and flame-resistant thermoplastic. It can produce about 

50% char up to 930°C. Chalcon II-polyarylate also has a very low heat release rate and high

char yield. It can be cured under UV/visible light, but the photo-cross-linking formed has no 

effect on the flammability. The thermal decomposition and flammability of copolymers and

terpolymers and blends change systematically with composition. The introduction of a

nonflammable, high-charring component (BPC II-arylate units) can conveniently control the 

flame retardance of these polymers. The total heat of combustion of the copolymers and 

terpolymers and blends changes linearly with composition. However, the change of peak value 

of heat release rate and char yield greatly depends on the chemical structures of the components. 

4-15/4-16
5. EFFECTS OF FLAME-RETARDANT ADDITIVES AND CORRELATIONS AMONG

PCFC, OSU, AND CONE CALORIMETERS.

5.1 INTRODUCTION. 

Flame-retardants have made a great contribution in reducing fire risk to people and property, but 

there is still plenty of room for improvement. Not only does fire still cause far too much 

damage, but the continuous development of new products creates a need for new or enhanced 

flame-retardant additives, especially nonhalogen flame-retardant additives. In addition, how to 

evaluate the efficiency of different flame retardants, such as the reduction of ease of ignition, 

burning or flame-spread rate, or smoke emission, and how these flame retardants act in a fire still 

remain complex topics. 

HRR is one of the most important variables that can determine the hazard from a fire [16]. A 

number of apparatus have been developed over the years for measuring heat release rate such as 

the OSU calorimeter ASTM E 906 [63], the cone calorimeter ASTM E 1354 [62] and the PCFC 

[64-66]. Because the heat release rate is not a property of a material and is influenced by

numerous external variables, the results from different methods are dependent not only on the 

physical and chemical characteristics of materials but also on the specific experimental 

conditions and procedures used. 

The OSU test was developed to obtain information on the heat release rate and visible smoke

from materials when exposed to different levels of radiant heat [63]. It is the required FAA HRR 

test for aircraft interior materials with large surface areas such as ceiling panels, wall panels, and 

stowage bins [18]. In the OSU test, the heat release rate is determined through thermal 

measurements (by thermopile). However, the thermopile measurement accounts for only the 

convective heat released by the specimen, thus missing the radiant heat component of the total 

HRR. 

The cone calorimeter is another significant bench-scale instrument in the field of fire tests. It 

measures the fire response of materials exposed to controlled levels of radiant heat fluxes 

ranging from 0~100 kW/m2

 [62]. It can determine the ignitability, heat release rates, total heat

released, mass loss rates, effective heat of combustion, visible smoke development, and carbon 

monoxide and carbon dioxide production of materials and products. The heat release rate is 

determined by measuring of the oxygen consumption (approximately 13.1 x 103

 kJ of heat are

released per 1 kg of oxygen consumed). By using the oxygen consumption principle as the 

method of measurement, the results are more precise and the apparatus does not need thermal

insulation because heat measurements are not required [62]. 

Generally, it is very difficult to compare the data from different fire test methods due to different 

experimental conditions and calculation procedures [120-122]. For example, OSU and cone

calorimeters all measure the fire response of materials under different external heat fluxes, but 

specimen melting, sagging, or falling out of the frame could cause problems in the OSU test due 

to the vertical mounting of specimen. In addition, the impinging pilot flame in the OSU test

creates a higher, localized heat flux near the bottom of the specimen, which can cause sooting, 

deterioration of orifices, and contribute to the heat release rate [63]. Furthermore, the pilot flame 

can be easily blown out during combustion. An electric spark commonly used in the cone 

5-1
calorimeter test is free of most of these difficulties. In the PCFC method, the pyrolysis is limited 

to small samples, and there is no temperature gradient and no mass transfer limitations. Hence,

the intrinsic material properties can be evaluated. However, because the pyrolysis and

combustion processes are totally separated in PCFC, the effects of some physical processes in a 

fire that are associated with the sample thickness, physical properties of materials, char buildup, 

heat and mass transfer, and heat feedback from the flame will not be shown in the results. In all, 

conflicting results from different methods may be due to different factors such as specimen 

orientation, specimen size, imposed heat flux, and some other burning characteristics of the 

specimens including melting and char formation. Despite these difficulties, it is important to 

understand the relationships among the various test methods and to learn how to interpret the 

results from these methods. 

In this section, the fire behavior of several commercial heat-resistant engineering thermoplastics, 

including poly(ether ether ketone) (Victrex PEEK), Xydar, and polyphthamide (Amodel

PPA) as well as their inert fiber-reinforced or flame-retarded composites, were measured by

OSU, cone, and PCFC calorimeters. The flammability of PMMA/clay nanocomposites and 

epoxy/phosphates composites were also studied. The purpose was to gain some fundamental 

information on the applicability of different test methods and understand the flame-retardant 

mechanisms of different additives. 

5.2 EXPERIMENTAL.

5.2.1 Test Samples. 

A list of samples is shown in table 5-1, which includes the details such as the structures, the 

presence or absence of flame-retardant additives, fillers, and the proportion of major inorganic 

components. Polysulfones (Udel P-1700, Radel A-300, Radel R-5000), Xydar, and 

polyphthamide (Amodel PPA) resins were supplied by BP Amoco Polymers Inc. (now Solvay 

Advanced Polymers, L. L. C.). Poly(ether ether ketone) (Victrex PEEK) was obtained from 

Victrex PEEK Inc. In addition, PMMA/clay nanocomposites [123] were provided by the U.S. 

Army Reserch Laboratory. Epoxy/phosphates composites were provided by Adam Zerda [124] 

of the University of Massachusetts, Amherst. 

5.2.2 Sample Preparation.

All the sample plaques for cone and OSU calorimeter tests were made by injection molding (BP 

Amoco Polymers Co.) or hot pressing. After conditioning to moisture equilibrium (constant 

weight), each specimen was wrapped in aluminum foil so that only the top surface was exposed,

while the bottom and sides of the specimen were covered with foil. 

5.2.3 Characterization.

The experimental conditions for TGA, STA, pyrolysis GC/MS, and PCFC measurements were

the same as those described in section 2.3. The OSU and cone calorimeter tests were performed 

at the FAA William J. Hughes Technical Center in Atlantic City International Airport, NJ. 

5-2
TABLE 5-1. SAMPLE COMPOSITIONS 

Polymers Structure and Description 

PEEK 

PEEK-GL30 PEEK with 30% glass fiber 

PEEK-CA30 PEEK with 30% carbon fiber 

Xydar

Xydar-G930 Xydar

 with 30% glass fiber 

Xydar-M345 Xydar

 with 45% mineral 

PPA A-1000 

A-1133 HS A-1000 with 33% glass fiber, 0%-10% titanium dioxide and a very small 

amount heat stabilizer. 

A-1145 HS A-1000 with 45% glass fiber and a very small amount of heat stabilizer. 

AF-1133 V-0 A-1000 with 33% glass fiber, 10%-30% polybrominated compound, 3%-7% 

calcium metasilicate, 0%-5% titanium dioxide, and 0%-5% zinc sulfide. 

AF-1145 V-0 A-1000 with 45% glass fiber, 10%-20% polybrominated compound, and 3%-

7% calcium. 

PPA A-6000 

A-6135 HS A-6000 with 35% glass fiber and a very small amount of heat stabilizer. 

A-6145 HS A-6000 with 45% glass fiber and a very small amount of heat stabilizer. 

A-6133 V-0 A-6000 with 33% glass fiber, 10%-30% brominated compound, 1%-5% 

antimony compounds, 0%-10% titanium dioxide, and 0%-10% zinc sulfide. 

A-6145 V-0 A-6000 with 45% glass fiber, 10%-30% brominated compound, 0%-5% 

antimony compounds, 0%-5% titanium dioxide, and 0%-5% zinc sulfide. 

Udel P-1700 

Radel A-300 

Radel R-5000 

O O C

O

n

C

O

O O C

O

C

O

O n

NH C

O

(CH2)4 C

O

NH (CH2) NH C 6

O

C

O

NH (CH2) C N C H 6 NH

O O

(CH2)6

25 65 10

NH C

O

(CH2)4 C

O

C NH (CH2)6

O

C

O

NH (CH2)6 NH

55 45

C

CH3

CH3

O S

O

O

O

n

S

O

O

O S

O

O

O

n

O S

O

O n

O

5-3
5.2.3.1 Ohio State University Calorimeter Test.

The specimen was 152 mm (6 inches) square and 1.6 mm (1/16 inch) thick (about 70-90 g) and 

was supported vertically in a metal frame. It was exposed to an external radiant heat flux of 35 

kW/m2

. Ignition of test specimens was achieved by direct flame impingement of a gas pilot. 

The HRR was measured for 5 minutes after the specimen was injected into the controlled

exposure chamber. Three important flammability parameters were reported: the maximum heat 

release rate during the 5-minute test, the total heat released during the first 2 minutes, and the 

total heat released for the entire 5 minutes. 

The HRR results can be obtained by two kinds of measurements: thermopile and oxygen 

depletion [125]. The thermopile was used to measure the convective portion of the heat release

through the temperature difference between the air entering and leaving the environmental

chamber, therefore resulting in lower reported values of heat release than oxygen depletion. 

h

m b

convective K

A

V V H × − ∆ = ( ) (5-1)

where Vm is the measured thermopile voltage during the test, Vb is the thermopile baseline 

voltage averaged over 20 seconds immediately before specimen injection, A is the surface area of 

specimen (0.02323 m2

 for 6′′ by 6′′ by 1/16′′ sample), and Kh is the calibration factor. However, 

besides the convective heat released, the total heat also includes the radiant heat absorbed by the 

apparatus. This is sometimes quite substantial, especially when the material burns with a highemissivity flame, i.e., a smoky flame [125]. 

(5-2) ∆Htotal = ∆Hconvective + ∆Hradiative

Oxygen depletion measurements can be used to calculate total heat released. The principle is 

similar to the cone and PCFC methods. 

oxygen

m b

total K

A

C C H × − ∆ = ( ) (5-3)

where Cm is the measured concentration of oxygen during the test, Cb is the baseline 

concentration determined by averaging the 20 data points immediately before specimen 

injection, and Koxygen is the constant of 13.1 kJ/g-O2 [125]. 

5.2.3.2 Cone Calorimeter Test.

The test specimen was 102 mm (4 inch) square and 1.6 mm (1/16 inch) thick (about 15-30 g). 

The wrapped specimen was placed into the sample container over a ceramic fiber blanket to 

prevent heat loss through the specimen back face, which can have an influence on the burning 

rate [62]. Specimens in the test were burned in ambient air conditions. Each material was tested

in the horizontal orientation at the external heat flux of 50 kW/m2

 in the presence of a spark 

ignition source. Some materials of interest were also tested at external heat fluxes of 75 and 100 

kW/m2

. The error band was ±10% compared to the true value. Two repeats were carried out for 

5-4
each test. The effective heat of combustion was determined from a measurement of specimen 

mass loss rate in combination with the heat release rate. Smoke development was measured by

obscuration of light by the combustion product stream. Ignition was determined as a

measurement of time from initial exposure to time of sustained flaming (existence of flame on or 

over most of the specimen surface for periods of at least 4 seconds). 

5.3 RESULTS.

5.3.1 Poly(Methyl Methacrylate)/Clay Nanocomposites. 

Layered silicate minerals, montmorillonite clays, and micas have recently received much 

attention as possible flame retardants. Most polymer layered silicate (clay) nanocomposites

show retardation of heat release rate during burning. The PMMA/clay nanocomposites studied 

here were made by emulsion polymerization or melt extrusion to achieve molecular-level 

incorporation of the layered silicate into the polymer [123]. Two kinds of nanomorphology can 

be induced: exfoliated structure by emulsion polymerization or intercalated structure by melt 

extrusion. PMMA/MMT (montmorillonite) and PMMA/FH (fluorohectorite) nanocomposites

were made by emulsion polymerization, while in PMMA/M18 (C18 modified MMT) and 

PMMA/F18 (C18 modified FH), PMMA matrix is a commercial PMMA made by melt extrusion. 

All the composites contain only 5 wt% clay. 

The thermal decomposition processes of PMMA/clay nanocomposites are shown in figure 5-1. 

It can be seen that they all produce about 5% char, which is exactly the amount of clay used. 

The thermal stability of PMMA/MMT composite is slightly increased, but the other 

nanocomposites start to decompose at lower temperatures than PMMA. The clay did not change

the major decomposition step of PMMA, but it can slightly decrease the decomposition rate 

(mass loss rate). 

The flammability of PMMA/clay nanocomposites is shown in table 5-2. Adding only 5 wt% 

clay does not change the total heat of combustion, but it can reduce the heat release rate, which is 

mainly due to the reduction of mass loss rate. It is believed that the layered clay can efficiently

slow the release rate of the volatiles due to its physical constriction effects [126]. Therefore, the

extruded composites that have layered structures show a 40% decrease in flammability. 

However, the emulsion composites show less decrease in flammability due to their exfoliated 

structures. Compared with FH, MMT is more effective in reducing flammability. 

Although PMMA-control (a commercial PMMA) and PMMA made by emulsion polymerization 

are the same kind of polymer, they have very different flammability and thermal stability. It was 

found that the major differences between these two materials are their molecular weights and 

molecular weight distributions. PMMA made by emulsion polymerization has a higher 

molecular weight and broader molecular weight distribution (table 5-3). Therefore, it starts to

decompose at lower temperatures due to its low molecular weight fraction. The effects of 

molecular weight of PMMA on their flammability are explained in detail in section 6.

5-5
0 100 200 300 400 500 600

-100

-50

0

50

100

Emulsion

(Exfoliate)

Temperature (oC)

Weight (

%)

 PMMA

 PMMA-MMT

 PMMA-FH

0

10

20

30

40

Deriv. of Weight (%/min)

100 200 300 400 500

-100

-50

0

50

100

Temperature (oC)

Weight (

%)

 PMMA

 PMMA-M18

 PMMA-F18

0

10

20

30

40

Extrusion

(Intercalated)

Deriv. of Weight (%/min)

FIGURE 5-1. THERMAL DECOMPOSITION OF PMMA/CLAY NANOCOMPOSITES 

TABLE 5-2. FLAMMABILITY AND THERMAL DECOMPOSITION OF PMMA/CLAY 

NANOCOMPOSITES

Methods Samples

H.R. 

Capacity 

(J/g-K) 

Total 

Heat 

(kJ/g) 

Char 

Yield 

(%) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax* 

(°C) 

T99%** 

(°C) 

PMMA-control 730 24 0 3.9 378 303

Extruded PMMA-F18 464 24 2.3 3.3 386 259

PMMA-M18 421 24 4.0 3.1 390 268

PMMA 479 24 0 3.2 379 208

Emulsion PMMA-FH 446 23 5.8 2.9 377 200

PMMA-MMT 331 23 5.6 3.0 371 232

*Temperature at maximum mass loss rate. 

**Temperatures at 5% weight loss. 

5-6
TABLE 5-3. GEL PERMEATION CHROMATOGRAHY GPC RESULTS OF PMMAs 

Polymers 

Number Average Molar Mass 





 





Mole

kg Polydispersity 

Index 

PMMA-control 59 2

PMMA-emulsion 166 4.4

5.3.2 Poly(Ether Ether Ketone) and Composites.

Obviously, inert fillers can reduce fuel content and act as heat sinks. However, many minerals 

and synthetic inorganic additives do exert further effects [7]. In charring systems, it was 

observed that fillers can suppress melt viscosity, heat radiation, and modification of the physical 

structure of the char. For example, glass fiber can prevent melt flow and dripping so that the 

flame-spread can be reduced in a fire. In this section, the effects of glass and carbon fibers on 

the thermal decomposition and flammability of PEEK are described. 

5.3.2.1 Thermal Decomposition Process.

According to figure 5-2, PEEK and its composites are a group of materials with very high 

thermal stability. Their onset decomposition temperatures are approximately 575°~580°C. Char 

yields of these polymers are all above 40%, especially for the composites containing 

nonflammable glass or carbon fiber. The maximum mass loss rates of the glass or carbon fiber 

PEEK composites are significantly reduced. 

0 200 400 600 800 1000

0

20

40

60

80

100

Temperature (oC)

Weight (

%)

 PEEK

 PEEK-GL30

 PEEK-CA30

0

10

20

30

40

Deriv. of W

eight (%/min)

FIGURE 5-2. THERMAL DECOMPOSITION OF PEEK AND ITS 

COMPOSITES IN N2

5-7
When PEEKs are burned in air, their thermal decomposition behavior is different from that in N2

(figure 5-3). They all show a two-step decomposition process. The first step is the same as the 

major decomposition in N2, and the second step is due to the oxidation of the carbonaceous char 

formed at the end of the first step. In contrast with the zero char yield of PEEK and carbon fiberreinforced PEEK, there is still about 30% char left at high temperatures in glass fiber-reinforced 

PEEK. That indicates that carbonaceous char and carbon fiber can be easily oxidized in air, but 

glass fiber has a strong resistance to oxidation. 

0 200 400 600 800 1000

-100

-50

0

50

100

Temperature (oC)

Weight (

%)

 PEEK

 PEEK-GL30

 PEEK-CA30

0

10

20

30

40

Deriv. of Weight (%/min)

FIGURE 5-3. THERMAL DECOMPOSITION OF PEEK AND ITS COMPOSITES IN AIR 

The heat events during the decomposition of these PEEK materials are very complex, which 

might include a series of endothermic and exothermic reactions (figure 5-4). 

100 200 300 400 500 600 700 800 900 1000

PEEK

PEEK-GL30

PEEK-CA30

Exothermic up

Temperature (oC)

FIGURE 5-4. HIGH-TEMPERATURE DSC CURVES OF PEEKs 

5-8
The thermal decomposition properties of PEEK and its composites are summarized in table 5-4. 

TABLE 5-4. THERMAL DECOMPOSITION PROPERTIES OF PEEKs 

In N2 In Air

Polymer T99% / 

T95%(1) 

(°C) 

Tmax

 (2)

(°C) 

PMLR (3)

(x103

/s) 

Char 

(%) 

∆H 

(J/g) 

T99%/ 

T95%(1)

(°C) 

T2

 (4)

(°C) 

Tmax

 (2)

(°C) 

PMLR(3)

(x103

/s) 

PEEK 565 

582 599 2.78 41 - 531 

567 618 586 2.28

PEEKGL30 562 

584 599 1.99 63 - 526 

568 625 654 1.64

PEEKCA30 554 

573 587 1.19 67 185 531 

561 605 636 3.01

(1) Temperatures at 1% and 5% weight loss.

(2) Temperature at maximum mass loss rate. 

(3) Maximum mass loss rate. 

(4) Onset of decomposition temperature of the second step.

5.3.2.2 Decomposition Products.

The major decomposition products of PEEK and its composites are the same: CO2, CO, phenol, 

and some aromatic ethers. At very high heating rates, the polymer will release more volatiles 

with low molecular weight, such as benzene and toluene. At the temperature of maximum mass 

loss rate, the major volatiles are CO2, CO, and phenol. Figure 5-5 shows the GC/MS traces of 

PEEK under different pyrolysis conditions. 

5.3.2.3 Flammability Measured by the PCFC Test.

According to the PCFC results (table 5-5), the introduction of glass and carbon fibers can further 

reduce the flammability of PEEK. Especially the 30% carbon fiber, which can bring the heat 

release capacity down by about 50%. To determine whether the flammability reduction of these 

composites is purely due to the mass-dilution effect of the inert fillers, the experimental values 

were compared with the calculated values. The values in the parentheses were calculated by 

deducting the contribution of the inert fillers on a mass basis. It can be seen that for PEEKGL30, the measured heat release capacity and total heat released are all very close to the 

calculated values, indicating the flammability reduction of PEEK-GL30 is purely due to the 

mass-dilution effect of the glass fiber, but the carbon fiber can further reduce the heat release 

rate. 

5.3.2.4 Flammability Measured by the Cone Calorimeter Test.

The cone calorimeter results of PEEK and its composites are listed in table 5-6 and shown in 

figure 5-6. The heat release rate (PHRR and HRRav) and total heat released (THR) indicate how 

fast and how much heat is generated during combustion. The effective heat of combustion of 

5-9
pyrolysis gases (EHC), smoke extinction area (SEA), and CO/CO2 ratio indicate the gas-phase 

combustion efficiency. 

CO2, CO 

OH

O

O

O

O

(a) 

(b) OH

O

C

O

CO2

CO 

OH

(c) 

CO2, CO 

FIGURE 5-5. PYROLYSIS GC/MS TRACES OF PEEK (a) 300°-930°C, 4.3°C/s; 

(b) 300°-930°C, 10°C/ms; and (c) 585°-590°C, 10°C/min 

5-10
TABLE 5-5. FLAMMABILITY OF PEEKs MEASURED BY PCFC 

Polymers 

H. R. Capacity

(J/g-K) 

Total Heat Released 

(kJ/g) 

PEEK 282 12

PEEK-GL30 188 (197) 9 (8) 

PEEK-CA30 110 (197) 8 (8) 

Note: The values in the parentheses were calculated by deducting the mass-dilution effect of the inert fillers. For example, the

heat release capacity of PEEK-GL30 is equal to the product of the heat release capacity of PEEK (282 J/g-K) and the weight 

fraction of the polymer matrix (70%). 

TABLE 5-6. FLAMMABILITY OF PEEKs MEASURED BY THE CONE CALORIMETER 

Polymer 

tig

(1)

(s) 

PHRR(2)

(kW/m2

) 

HRRav (3)

(kW/m2

) 

THR(4)

(MJ/m2

) 

MLR(5)

(g/m2

-s) 

PEEK 70 543 103 22.4 4.72

PPEK-GL30 84 133 41 11.2 2.32

PEEK-CA30 67 104 37 9.78 2.39

Polymer 

EHC(6) 

(kJ/g) 

SEA(7)

(m2

/kg) CO/CO2

PEEK 20.8 451 0.131

PPEK-GL30 15.6 355 0.117

PEEK-CA30 15.4 189 0.164

(1) Time to ignition using pilot spark. 

(2) Peak heat release rate. 

(3) Mean values from tig to 180 sec. after.

(4) Total heat released.

(5) Average mass loss rate. 

(6) Effective heat of combustion calculated from total heat release and overall mass loss. 

(7) Smoke-specific extinction area. 

0 100 200 300 400

0

100

200

300

400

500

600

PEEK-CA30

PEEK-GL30

PEEK

HRR (k

W/m2

)

Time (s)

FIGURE 5-6. CONE HRR CURVES OF PEEK AND ITS COMPOSITES

5-11
It can be seen that the carbon fiber does not affect ignition time, but the glass fiber can greatly

increase the time delay to ignition. However, the heat release rate and total heat released of 

fiber-reinforced composites are all reduced by more than 50% with only 30% inert fillers. 

Therefore, the decrease in their flammability in the cone calorimeter test is not only attributed to

the mass-dilution effect of the fillers (the reduction of the amount of burning materials

available), but it is also due to some other effects. It is known that the char can insulate the

polymer substrate from heat and oxygen and reduce the release rate of the volatiles. As a result, 

the increase of the char formation can greatly improve the fire resistance of materials. In the

PCFC test, very small amount of samples are used and the heat generated from combustion 

cannot transfer back to the sample, so the heat and mass transfer barrier effects of the char cannot 

be realized in this test. However, in the cone calorimeter test, relatively large amounts of 

samples are used; therefore, the materials can form a discrete layer of char on the top, which will 

give good protection to the underlying materials from heat and flame. 

In summary, in the PCFC test, the glass and carbon fibers mainly act in the condensed phase by 

mass-dilution effect. In the cone calorimeter test, the char formed can further slow down 

polymer decomposition by acting as a heat and mass transfer barrier. 

5.3.3 Xydar

 and Its Composites.

5.3.3.1 Thermal Decomposition Process. 

Xydar liquid crystalline polymer has excellent thermal stability and inherent flame retardancy.

Xydar and its 30% glass-reinforced and 45% mineral-filled composites all decompose in a 

single step with a high onset decomposition temperature of 500°C in N2 (figure 5-7). They all 

can produce more than 40% char. The inert fillers can further increase the char formation and 

reduce the mass loss rates, but they did not affect the thermal stability of the materials. 

0 200 400 600 800 1000

0

20

40

60

80

100

Temperature (oC)

Weight (

%)

 Xydar

 Xydar G-930

 Xydar M-345

0

10

20

30

Deriv.

of Weight (

%/min)

FIGURE 5-7. THERMAL DECOMPOSITION OF XYDAR AND ITS COMPOSITES IN N2

5-12
During decomposition, Xydar and its composites all show two overlapped endothermic peaks 

(figure 5-8). The introduction of inert glass or mineral fillers can reduce the amount of the heat 

absorbed during decomposition (table 5-7). 

200 400 600 800

Xydar M-345

Xydar G-930

Xydar

Exothermic

Temperature (oC)

FIGURE 5-8. HIGH-TEMPERATURE DSC CURVES OF XYDAR AND ITS COMPOSITES

TABLE 5-7. THERMAL DECOMPOSITION PROPERTIES OF XYDAR

MATERIALS IN N2 

Polymers 

T99%

(°C) 

T95%

(°C) 

Tmax

(°C) 

PMLR 

(x103

/s) 

Char 

(%) 

∆H 

(J/g) 

Xydar 478 501 525 2.55 40 163

Xydar G-930 477 509 524 1.83 59 135

Xydar M-345 471 495 504 1.54 66 104

Similar to PEEK and its composites, Xydar and its composites all decompose in two steps in air

(figure 5-9). The first step is the same as the major decomposition step in N2. The second step is 

due to the oxidation of the carbonaceous char formed at the end of the first step. Because the 

glass fiber and mineral are very difficult to oxidized, both Xydar composites still have a large

amount of char left at high temperatures, which is exactly the same as the amount of inert filler 

incorporated. In air, the glass or mineral-filled composites decompose faster in the second step,

which is different from the pure Xydar polymer (table 5-8). 

5-13
0 200 400 600 800 1000

-100

-50

0

50

100

Temperature (oC)

Weight (

%)

 Xydar

 Xydar G-930

 Xydar M-345

0

5

10

15

20

25

30

Deriv. of Weight (

%/min)

FIGURE 5-9. THERMAL DECOMPOSITION OF XYDAR MATERIALS IN AIR 

TABLE 5-8. THERMAL DECOMPOSITION PROPERTIES OF XYDAR 

MATERIALS IN AIR 

Polymers 

T99%

(°C) 

T95%

(°C) 

T2

(°C) 

Tmax

(°C) 

PMLR 

(x103

/s) 

Char 

(%) 

Xydar 472 498 571 522 2.45 0

Xydar G-930 447 498 566 580 2.23 28

Xydar M-345 465 495 582 593 1.73 45

5.3.3.2 Flammability Measured by the PCFC Test.

Because Xydar G-930 contains more polymer components and has a higher maximum mass

loss rate, it is more flammable than Xydar M-345 from PCFC method (table 5-9). According to 

pyrolysis GC/MS results (figure 5-10), the flammability of Xydar materials mainly comes from

the phenol volatile. Similar to PEEK composites, the flammability reduction of the Xydar

composites measured by the PCFC test is mainly due to the mass-dilution effect of the 

nonflammable glass or mineral fillers. 

TABLE 5-9. FLAMMABILITY OF XYDAR AND ITS COMPOSITES BY PCFC 

Polymers H. R. Capacity (J/g-K) Total Heat (kJ/g) 

Xydar 215 11

Xydar G-930 137 (151) 8 (8) 

Xydar M-345 120 (118) 6 (6) 

Note: The values in the parentheses are calculated by deducting the mass-dilution effect of the inert fillers. 

5-14
CO2, CO 

OH

OH

OH

C O

O

FIGURE 5-10. PYROLYSIS GC/MS TRACES OF XYDAR (4.3°C/s TO 930°C) 

5.3.3.3 Flammability Measured by the OSU Calorimeter Test.

In contrast to PCFC results, the OSU calorimeter test shows that Xydar M-345 is more 

flammable than Xydar G-930. In addition, Xydar G-930 has an extremely low 2-min heat 

release due to its slow burning rate at the beginning of the 2 minutes (figure 5-11). 

It was also found that the 5-minute heat release from Xydar G-930, measured by the OSU 

calorimeter (table 5-10), is smaller than the total heat released measured by the PCFC test. In the 

PCFC test, the pyrolysis and combustion temperatures are 930° and 900°C, respectively, so the 

materials are completely decomposed and the volatiles produced are totally oxidized. As a 

result, the total heat released measured by PCFC indicates the maximum flammability of

materials, based on their chemical structure and composition. However, in the OSU test, the 

burning process of most high-charring materials is not completed by the end of the 5-minute test.

The incomplete burning of Xydar G-930 can also be proven by the high char yield of 69% from

the OSU test versus 59% from the PCFC test. 

0 1 2345

0

50

100

150

Xydar G-930

Xydar M-345

HRR (kW/

m2

)

Time (s)

FIGURE 5-11. OHIO STATE UNIVERSITY HRR CURVES OF XYDAR

COMPOSITES BY THERMOPILE 

5-15
TABLE 5-10. OHIO STATE UNIVERSITY RESULTS OF XYDAR COMPOSITES 

Method Parameters Xydar m-345 Xydar G-930 

PHRR (kW/m2) 123 69

2-min HR (kW.min/m2 Thermopile ) 13 2

5-min HR (kW.min/m2

) 234 146

PHRR (kW/m2) 179 103

2-min HR (kW.min/m2 O2 consumption ) 37 14

5-min HR (kW.min/m2

) 275 208

Char (%) 69 69 

Nonetheless, why does Xydar M-345 have a lower mass loss rate but a higher heat release rate 

in the OSU test? It is probably because, besides the chemical structure and composition of

materials, there are some other factors, such as the physical properties of the materials and mass 

and heat transfer during burning that also affect the flammability. In the PCFC test, materials are 

forced to pyrolyze at a fixed heating rate, and the volatiles produced are completely oxidized in

the high-temperature furnace. In addition, the pyrolysis and combustion (oxidation) processes

are totally separated, thus, the heat generated by the combustion cannot be delivered back to the

polymer to further affect polymer decomposition. Therefore, the PCFC results are mainly 

determined by the chemical structure and composition of materials (mass loss rate, char yield,

and heat of combustion of volatiles). As a result, a high mass loss rate usually leads to a high

heat release capacity in the PCFC test if the materials have similar structures. However, the

OSU test is a real flame-combustion test, and the sample surface is directly exposed to the flame.

Therefore, the heat produced in the gas phase can feed back to form a real combustion cycle. 

Because Xydar M-345 is mineral-filled, it is more likely to absorb the heat from its 

surroundings to facilitate the decomposition and combustion process thereafter, which might lead 

to its high flammability.

5.3.3.4 Flammability Measured by the Cone Calorimeter Test.

The cone calorimeter results show that both Xydar M-345 and Xydar G-930 have very good 

flame resistance, but Xydar M-345 has a relatively higher heat release rate, which is consistent 

with the OSU results (table 5-11 and figure 5-12). The increase of the heat flux can increase heat 

release rate, mass loss rate, and total heat released but decrease the CO/CO2 ratio, which means

flammability and efficiency of combustion are both increased. 

5-16
TABLE 5-11. CONE CALORIMETER RESULTS OF XYDAR COMPOSITES 

Polymer 

Heat flux 

(kW/m2

) 

tig

(s) 

PHRR 

(kW/m2

)

HRRav

(kW/m2

)

THR 

(MJ/m2) 

MLR 

(g/m2-s) 

50 72 105 44 16.3 4.5

75 39 235 66 21.4 6.8 Xydar 

M-345 

100 26 228 72 20.0 8.1

50 50 92 50 19.6 3.8

75 25 137 74 25.0 6.1 Xydar 

G-930 

100 14 141 82 23.5 7.4

Polymer 

Heat Flux 

(kW/m2) 

EHC 

(kJ/g) 

SEA 

(m2/kg) CO/CO2

50 12.2 318 0.063

75 14.6 350 0.021 Xydar 

M-345 

100 14.1 365 0.015

50 15.2 251 0.047

75 16.0 405 0.011 Xydar 

G-930 

100 15.5 429 0.007

0 100 200 300 400 500 600

0

20

40

60

80

100

120

Xydar G-930

Xydar M-345

HRR (k

W/m2

)

Time (s)

FIGURE 5-12. CONE HRR CURVES OF XYDAR COMPOSITES 

5.3.4 Polyphthalamides and Composites.

Recently, halogenated flame retardants have been the subject of environmental concerns, but the 

effectiveness of these compounds has maintained their position in the market place. In this

section, two series of poly(phthalamide) materials (A-1000 and A-6000 series) with brominated 

flame retardants and/or glass fiber were studied. The composition of the materials was detailed 

in table 5-1.

5-17
5.3.4.1 Thermal Decomposition Process.

The TGA results show that all these materials decompose in a single step under N2 (figure 5-13). 

They all have relatively high thermal stability up to 400°C. The heat stabilizer does increase the 

thermal stability of materials. For example, the temperature at 5% weight loss for A-6135HS is

increased from 402°C (A-6000) to 421°C (A-6135HS). Correspondingly, the temperature at 

maximum mass loss rate is also increased from 453°C (A-6000) to 468°C (A-6135HS). On the 

contrary, the introduction of brominated flame retardants decreases the thermal stability and 

increases the mass loss rate if the reduction effect of the glass fiber is excluded. In addition, 

because A-1000 and A-6000 have zero char yield, the char of all the composites comes mainly 

from the nonflammable glass fiber. 

0 200 400 600 800 1000

-100

-50

0

50

100

Temperature (oC)

Weight (

%)

 A-1000

 A-1133HS

 A-1145HS

 AF-1133V-0

 AF-1145V-0

0

10

20

30

40

50

60

Deriv. of Weight (%/min)

(a) 

200 400 600 800

-100

-50

0

50

100

Temperature (oC)

Weight (

%)

0

10

20

30

40

 A-6000

 A-6135HS

 A-6145HS

 AFA-6133V-0

 AFA-6145V-0

Deriv. of Weight (%/min)

(b) 

FIGURE 5-13. THERMAL DECOMPOSITION OF PPA MATERIALS (a) A-1000 SERIES 

AND (b) A-6000 SERIES

5-18
High-temperature DSC curves of A-1000, A-6000, and some of their flame-retardant and/or 

glass-fiber composites are shown in figure 5-14. All the materials exhibit an endothermic 

decomposition peak. The introduction of glass fiber can reduce the heat of decomposition due to

the lower amount of fuel available. The presence of flame retardants can make the

decomposition peak sharper. In addition, the melting peaks (around 340°C) in the flameretardant composites have disappeared. 

200 300 400 500 600 700

AFA 6133V-0

A-6135 HS

A-6000

AF 1133V-0

A-1000

Exo up

Temperature (oC)

FIGURE 5-14. HIGH-TEMPERATURE DSC CURVES OF PPA MATERIALS 

5.3.4.2 Thermal Decomposition Products.

The GC/MS traces of A-1000, A-6000, and their composites under different pyrolysis conditions 

are shown in figure 5-15. The major decomposition products of A-1000 and A-6000 are similar, 

including CO2, CO, some aliphatic olefins, benzonitriles (typical volatiles for amides), and a 

series of aromatic-aliphatic amides with different lengths of CH2 units. A-6000 also releases 

more hexanedinitrile than A-1000. The decomposition products of the glass fiber-reinforced

composites are the same as those from virgin polymers. Therefore, the decrease in the heat 

release capacity and total heat released of these composites is only due to the mass dilution effect 

of the glass fiber. However, the major decomposition products of the flame-retardant composites

are quite different. For AFA-6133 V-0 and AFA-6145V-0, bromostyrenes, 

dibromobenzonitriles, and tribromobenzonitrile are the predominant volatiles. In contrast, AF1133 V-0 and AF-1145 V-0 release not only some brominated compounds such as 

dibromobenzonitriles and tribromobenzonitrile, but also a certain amount of other aromatic 

compounds. At the temperature of maximum mass loss rate, these flame-retardant materials 

mainly produce brominated volatiles. 

5-19
FIGURE 5-15. PYROLYSIS GC/MS TRACES OF PPA MATERIALS 

(PYROLYSIS CONDITION: 300°~930°C AT A HEATING RATE OF 4.3°C/s FOR 

(a) A-1000; (b) A-6000; (c) AF-1133 V-0; (d) AFA-6133 V-0, 10°C/min FOR 

(e) AF-1133 V-0, 400°~405°C; AND (f) AFA-6133 V-0, 405°~410°C) 

5-20
5-21

(e) AF-1133 V-0, 400°~405°C; AND (f) AFA-6133 V-0, 405°~410°C) (Continued) 

FIGURE 5-15. PYROLYSIS GC/MS TRACES OF PPA MATERIALS 

(PYROLYSIS CONDITION: 300°~930°C AT A HEATING RATE OF 4.3°C/s FOR 

(a) A-1000; (b) A-6000; (c) AF-1133 V-0; (d) AFA-6133 V-0, 10°C/min FOR 
5.3.4.3 Flammability Measured by PCFC Test. 

The thermal decomposition and flammability of PPA materials are summarized in table 5-

can be seen that the heat release capacity of A-1000 is slightly higher than that of A-6000 

because A-1000 contains more aliphatic units. The reduction in the heat release capacity and 

total heat released of A-6135HS, 6145 HS, 1135HS, and 1145HS is completely due to the m

dilution effect of glass fiber (the measured values are close to the calculated values in th

parentheses). 

TABLE 5-12. THERMAL DECOMPOSITION AND FLAMMABILITY OF PPA MATERI

Polymers 

T99% 

(°C) 

T95%

(°C) 

Tmax

(°C) 

PMLR 

(x103

/s) 

Char 

(%) 

H. R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

A-1000 387 427 476 4.15 0 610 

A-1133 HS 399 431 476 2.91 (2.78) 34 408 (409) 22 (21) 

A-1145 HS 404 435 473 2.45 (2.28) 45 349 (336) 17 (17) 

AF-1133 V-0 363 394 403 3.91 (2.78) 36 394 (409) 13 (21) 

AF-1145 V-0 368 414 429 4.59 (2.28) 48 444 (336) 11 (17) 

A-6000 372 402 453 3.06 0 537 

A-6135 HS 389 421 468 2.42 (1.99) 35 365 (349) 21 (22) 

A-6145 HS 371 419 463 2.14 (1.68) 44 301 (295) 18 (18) 

AFA-6133 V-0 334 389 410 3.30 (2.05) 39 265 (359) 13 (22) 

AFA-6145 V-0 368 388 401 2.64 (1.68) 49 209 (295) 10 (18) 

ues in the parentheses are the product of the property of the base polymers (A-1000 or A-6000) and the

fraction of polymer matrix. 

The brominated flame retardants can reduce the total heat released, but their effects on th

release capacity are more complicated. For AFA-6133 V-0 and AFA-6145 V-0, the heat release 

capacity is further reduced even after excluding the contribution of the glass fiber. However, for 

AF-1145 V-0, the measured heat release capacity is higher than the calculated value, which 

indicates that the introduction of polybrominated flame retardant actually increases the

flammability after the deduction of mass-dilution effect of the glass fiber. This is because th

easurement is not a real flame-combustion test. All the pyrolysis gases produced can be

pletely oxidized in the high-temperature furnace. Therefore, the instantaneous gas-ph

inhibition of the halogenated flame retardants will not be achieved in the PCFC test. As a resu

the sharp and high mass loss rate peaks in these flame-retarded materials might induce high hea

ase rates. However, because the major decomposition volatiles from these flame-retarde

terials are halogenated compounds that have relatively lower flammability than corresponding 

12. It 

asse 

ALS 

31 

33 

*Val weight

e heat 

e

PCFC m

com ase 

lt,

t

rele d

ma

ydrocarbon volatiles, the total heat released of these materials can still be reduced. It was also 

found that t AFA-6133

V-0 a CFC

results. 

h

he combination of brominated compounds with antimony compounds in

nd 6145 V-0 can synergistically reduce flammability, which is also shown in the P

5-22
5.3.4.4 Flammability Measured by the OSU Calorimeter Test. 

rocess in the OSU test, AF-1133 V-0 shows a dramatic decrease in both heat 

elease rate and total heat released (table 5-13). However, a lot of smoke was also produced. 

TABLE 5-13. FLAMMABILITY OF A-1000 SERIES MEASURED BY 

H U C ET

Method ara rs A-1000 133 V-0 

A-1000 and A-6000 are very flammable and dripped extensively during the OSU test.

Therefore, their flammability measured by the OSU test is underestimated because some melt 

falls to the bottom of the furnace and are not burned. After adding 33% glass fiber and 30%

flame retardant, the dripping problem of AF-1133 V-0 is greatly reduced. Because the

brominated volatiles released during decomposition can act in the gas phase and slow down the 

combustion p

r

T E OS ALORIM ER

P mete AF-1

Thermopile PHRR (kW/m ) 19 2 0 110

2-min HR (kW.min/m ) 13 2 6 94

5-min HR (kW.min/m ) 35 2 9 275

O2 consumption PHRR (kW/m ) 41 2 7 262

2-min HR (kW.min/m 30 228 2) 5

5-min HR (kW.min/m ) 51 2 4 494

Char (%) 0 40

-reta d AF 133 V-0 ha a lo and broade ning pea

figure 5-16). Th ar of F-113 V-0 c n hold togeth , so

It was found that the flame rde -1 d wer r bur k

( e ch A 3 a er the shape and size of the burned 

sample were the same as the original sample. Interestingly, the char had a two-layered structure 

a by the polymer matrix and brominated flame retardant. 

in which the surface layer is the white char formed by the glass fiber and underneath is the black 

c rbonaceous char formed

012 3 4 5

0

50

100

150

200

250

AF-1133 V-0

A-1000

HRR (kW/m2) (Thermopile)

Time (s)

FIGURE 5-16. OHIO STATE UNIVERSITY HRR CURVES OF A-1000 SERIES 

5-23
According to the OSU results of A-6000 series (table 5-14), A-6135 HS and A-6145 HS have

higher flammability than A-6000. This is because the glass fiber can reduce the flammability

rve 

ore burning materials available. As a result, high flammability is observed in OSU results. 

TABLE 5-14. FLAM ES MEASURED BY

THE OSU CALORIMETER 

A-60 A-6145 HS FA-6133 V-0 A-6145 V-0

mainly by its nonflammable property. Generally, it cannot induce char formation in the polymer 

matrix or act in the gas phase. Therefore, the glass fiber cannot change the thermal

decomposition mechanism or gas-phase combustion of the materials. However, the

incorporation of glass fiber does change the physical properties of materials. For example, the 

increase of the thermal conductivity can increase the composite’s ability to absorb the heat and

spread the heat along the sample. This might increase the decomposition rate of the material and 

speed up the burning process. On the other hand, the reduction of the dripping will also rese

m

MABILITY OF A-6000 SERI

Method 00 A-6135HS A AF

RR

W/m2

) 1 207

202 220 

min HR 

Thermopile

PH

(k 98 232 90 93 

2-min HR 

(kW.min/m2

) 161 96 96 

5-

(kW.min/m2

) 375 480 493 250 247 

O2 consumption 

PHRR 

(kW/m2

) 411 420 433 306 289

2-min HR 

2 293 362 379 312 (kW.min/m ) 269 

5-min HR 

(kW.min/m

2

) 521 673 606 548 490 

Char (%) 0 31 44 39 49 

For the flame-retardant composites (AFA-6133 V-0 and AFA-6145 V-0), their flammability is

dramatically reduced due to the synergetic effects of brominated compounds and antimony 

compounds. They all show a low and steady heat release peak during burning (figure 5-17). 

Their two-layered char is similar to AF-1133 V-0, while only white fragmented char is formed in 

A-6135 HS and A-6145 HS. 

5-24
0 1 3 4 5

s)

FIGU OHIO E UN Y HR S O IES

4.5 Flamma easu the C imete

s fiber or flame-retarded com

lease peak, but th e-reta

-0 is , whic me s

0

2

0

HRR (kW/m

Time (

100

150

200 A-6000

 A-6135 HS

 A-6145 HS

 AFA-6133 V-0

 AFA-6145 V-0

2) (thermopile)

50

RE 5-17. STAT IVERSIT R CURVE F A-6000 SER

5.3. bility M red by one Calor r Test. 

The cone HRR curves of the A-1000 series are shown in figure 5-18. It can be seen that all the 

glas posites are less ignition resistant than A-1000. A-1000 and the 

glass fiber-reinforced composites A-1135 HS and A-1145 HS all show a sharp and high heat 

re e flam rded composites AF-1133 V-0 and AF-1145 V-0 have a very low 

heat release rate. The burning peak in AF-1133 V very broad h suggests so teadyburning process. 

0 100 200 300 400

0

100

500

600

70

 A-1000

 A-1133HS

 A-1145HS

 AF-1133V-0 2

)

Time (s)

FIGURE 5-18. CONE HRR CURVES OF A-1000 SERIES 

200

300

400

 AF-1145V-0

HRR (kW/m

5-25
The cone HRR curves of the A-6000 series (figure 5-19) are similar to those of the A-1000 

series. The glass fiber-reinforced composites A-6135 HS and A-6145 HS have a lower heat 

release rate than A-6000, and the flame-retarded composites AFA-6133 V-0 and AFA-6145 V-0 

show a kind of steady-burning process with very low heat release rates. It seems that the peak

heat release rates of these flame-retarded composites are independent of the amount of glass fiber 

inside. 

0 100 200 300 400

400

600

800

1000

 A-6000

 A-6135HS

 A-6145HS

 AFA-6133V-0

 AFA-6145V-0

HRR (k

W/m2

)

200

0

Time (s)

FIGURE 5-19. CONE HRR CURVES OF A-6000 SERIES 

The cone calorimeter results of A-1000 and A-6000 and their composites are shown in

table 5-15. In the A-1000 series, the ignition time of both glass fiber-reinforced and flametarded composites is shorter than A-1000. The addition of glass fiber can reduce the mass loss

rate and total heat released due to the mass-dilution effect. However, due to the change of some 

physical properties of the materials, the peak heat release rates of A-1135HS and A-1145HS are 

not significantly reduced by the inert glass fiber. In addition, their effective heat of combustion 

and smoke evolution are the same as A-1000, which indicates that the decomposition volatiles

released, as well as the gas-phase combustion chemistry, are not changed. For the flameretarded composites AF-1133 V-0 and AF-1145 V-0, the flammability is greatly reduced by the 

polybrominated flame retardant. Their peak heat release rates are about three times lower than 

A-1000, the total heat released and effective heat of combustion are about 50% lower. In 

contrast, the smoke production is about two times higher, and the CO/CO2 ratio is about ten 

times higher. All these results suggest that the polybrominated flame retardant acts in the gasphase by the incomplete combustion. In other words, the brominated compounds released during 

decomposition can reduce the active, flame-carrying H⋅ and OH⋅ radicals from the propagation 

and chain-branching steps and replace them with less active bromine radicals. As a result, the

burning process is slowed in the gas phase. 

re

5-26
TABLE 5-15. CONE CALORIMETER RESULTS OF PPA MATERIALS 

Polymer 

Heat Flux 

(kW/m2

) 

tig 

(s) 

PHRR 

(kW/m

2

) 

HRRav 

(kW/m

2

) 

THR 

(MJ/m2) 

A-1000 50 39 685 262 48.2 

A-1135 HS 50 27 657 160 30.1 

A-1145 HS 50 23 612 115 20.9 

A-1133 V-0 50 37 198 100 21.7 

A-1145 V-0 50 31 222 63 12.1 

50 36 876 240 50.4 

A-6000 75 22 1231 258 51.1 

100 11 1794 338 60.8 

50 33 640 235 45.1 

A-6135 HS 75 16 805 250 45.1 

100 10 953 259 46.6 

A-6145 HS 50 34 505 207 41.4 

50 28 191 77 16.9 

A-6133 V-0 75 14 289 109 21.1 

100 11 323 107 20.2 

A-6145 V-0 50 31 181 69 15.0 

Polymer 

Heat Flux 

(kW/m

2

) 

MLR 

(g/m2-s) 

EHC 

(kJ/g) 

SEA 

(m2/kg) CO/CO2

A-1000 50 21.2 22.0 593 0.019 

A-1135 HS 50 10.3 22.8 535 0.030 

A-1145 HS 50 10.0 23.2 507 0.036 

A-1133 V-0 50 9.1 11.0 938 0.114 

A-1145 V-0 50 8.1 11.0 966 0.127 

50 15.9 25.0 525 0.016 

A-6000 75 10.1 25.0 621 0.013 

100 37.6 27.2 535 0.019 

50 11.9 26.7 505 0.022 

A-6135 HS 75 17.4 24.4 638 0.023 

100 19.6 25.7 644 0.022 

A-6145 HS 50 8.6 22.8 443 0.018 

50 9.0 8.6 1072 0.138 

A-6133 V-0 75 14.0 10.4 1231 0.160 

100 16.1 10.4 1237 0.169 

A-6145 V-0 50 7.81 9.0 1109 0.155 

In the A-6000 series, there is some decrease in the heat release rates of A-6135 HS and A-6145 

HS, and the amount of decrease in total heat released is not proportional to the amount of glass 

ber inside. As expected, the flame-retarded composites AFA-6133 V-0 and AFA-6145 V-0 

have a dramatic decrease in flammability. Their peak heat release rates were about four times 

lower than A-6000, the total heat released and effective heat of combustion were about 70% 

lower, the smoke production is twice as high, and the CO/CO2 ratio are ten times higher. The

combination of the brominated flame retardant with antimony compound in AFA-6133 V-0 and 

fi

5-27
AFA-6145 ffect the 

ombustion of polymers both in the gas and condensed phases. It can also be seen that with the 

increase of the heat flux, th se ra mass , and at rel ll increase,

but the effec at of c does cha tic

It can be concluded that the heat stabilizer can increase the thermal stability of materials. The

addition of glass fiber can reduce the flammability, mainly by mass-dilution effects. However, it 

can also change some physical properties of the materials such as thermal conductivity, density, 

and heat capacity. Therefore, the mass-dilution effect of the glass fiber observed in OSU and 

cone calorimeter tests is not as dramatic as in PCFC tests. Brominated compounds mainly act in 

the gas phase by reducing the combustion efficiency. The combination of brominated 

compounds with the antimony compound is more efficient due to their synergistic effect. 

However, the gas-phase inhibition effects of the brominated flame retardants can only be seen in

OSU and cone calorimeter tests, not in PCFC tests. 

5.3.5 Epoxy Resins With Phosphate Flame Retardants

V-0 is more effective because the antimony-halogen systems can a

c

e heat relea

ombust

te, loss rate

nge drama

total he eased a

tive of he ion not ally.

reta elp d he m

methy

trimethyl pho (TM triph

. 

Interest in halogen-free flame rdants h rive t arket toward phosphorus-based flame 

retardants. In this section, the effects of three different phosphates (dimethoxy l phosphate

(DMMP), sphate P), and enyl phosphate (TPP)) on the flammability of an

epoxy resin (EPON 825 cured by Jeffamine D230) were studied. In these systems, phosphates 

also serve as viscosity dep he c ites were made in three steps: (1) mixing the

three components together, g th at r a urs increasing

the temperature to 125°C for another 3 hours [124]. The structure ach co t is shown

in figure

FIGURE 5-20. COMP ION OF EPOXY RESIN 

The thermal decomposition p ses of nt epoxy/phosphate composites are shown in 

figure 5-21. It can be seen that with the increased amount of DMMP, TMP, or TPP, the thermal 

ability and mass loss rates of the composites decrease systematically. The phosphate additives

ressants. T

(2) heatin

ompos

e mixture 75°C fo bout 3 ho , and (3)

of e mponen

5-20.

OSIT PHOSPHATE-RETARDED

roces differe

st

tend to volatilize from the composites below 300°C due to their low boiling points (figure 5-22). 

The major decomposition step is due to the breakdown of the epoxy network, which releases a 

series of olefins and phenols. The char yields of expoxy/TMP resins increase with the 

concentration of TMP, which suggests that TMP can act in the condensed phase to reduce 

flammability. However, DMMP and TPP cannot significantly increase the char yields of the 

composites. 

5-28
500 600 700 800

Temperature (oC)

 9.9wt%

80

Der

50

100

 0

 3.5wt%

 6.8wt%

100

0 100 200 300 400

-100

-50

0

Weight (

%)

 12.7wt%

0

20

40

60

iv. of Weight (

%/min)

(a)

0 100 200 300 400 500 600 700 800

-100

-50

Temperature (oC)

 0

0

50

200

in)

100

0

50

Weight (

%)

 4wt%

 7.6wt%

 11wt%

 14.1wt%

100

150 Deriv. of Weight (%/m

50

100

ig %)

 0

 3.5wt%

 6.8wt%

 9.9wt%

 12.7wt%

150

200

Deriv. o

0 ig

ht (

100

f We

0 100 200 300 400 500 600 700 800

-100

-50

Temperature (oC)

We

0

50

ht (%/min)

FIGURE 5-21. THERMAL DECOMPOSITION OF EPOXY/PHOSPHATE COMPOSITES 

[12

(c)

4] (a) DMMP, 20°C/min; (b) TMP, 40°C/min; AND (c) TPP, 40°C/min 

(b)

5-29
5-30

P

O

H3CO CH3

OCH3

(a) 

CO2, CO 

NH2

OH

OH

HO OH

(b) 

FIGURE 5-22. PYROLYSIS GC/MS TRACES OF EPOXY/DMMP COMPOSITES 

(HEAT RATE, 4.3°C/s) (a) 150°~300°C AND (b) 300°~930°C 

According to table 5-16, the heat release capacity and total heat released are lower for all the 

composites by adding phosphate additives. The dramatic decrease of heat release capacity is due 

to the significant reduction of maximum mass loss rate. It was also found that the heat release 

capacity of epoxy/TMP composites changes linearly with the maximum mass loss rate, which

indicates that the flammability reduction is mainly due to the reduction of the decomposition rate 

in the condensed phase. 

The cone calorimeter results of epoxy/TMP are shown in table 5-17 and figure 5-23. It can be 

seen that adding only 4 wt% of TMP does not have a big effect on the flammability. Only when

the amount of TMP is increased to about 8 wt%, are the peak heat release rate and total heat

released dramatically reduced. The reduction of the effective heat of combustion and increase of

the CO production implies that besides the condensed-phase inhibition, TMP also acts in the gas 

phase by reducing the combustion efficiency. However, because the chars formed by all the

composites are extremely foamy and sometimes swell into the cone heater, the flammability

measured might not be accurate. 
TABLE 5-16. THERMAL DECOMPOSITION AND FLAMMABILITY OF 

EPOXY/PHOSPHATE COMPOSITES 

Additive wt% 

T99% 

(°C) 

T95%

(°C) 

Tmax

(°C) 

PMLR 

(x103

/s) 

Char 

(%) 

H. R. 

Capacity 

(J/g-K) 

Total 

heat 

(kJ/g) 

0 347 376 396 16 6 1100 27 

4 268 318 348 10 9 710 26 

7.6 242 303 346 9.6 11 680 25 

11 191 282 321 8.8 13 580 24 

TMPa

14.1 207 289 331 8.1 15 550 23 

0 334 359 388 8.3 6 1100 27 

3.5 205 322 372 4.6 7 470 25 

6.8 167 298 357 4.0 7 370 24 

9.9 148 266 349 3.7 8 370 24 

DMMPb

12.7 147 260 346 3.5 8 380 24 

0 347 376 396 16 6 1100 27 

3.5 287 342 374 11.4 7 880 26 

6.8 258 329 365 11.0 7 700 25 

9.9 236 318 356 10.3 8 620 26 

TPPc

12.7 216 295 358 9.7 8 740 25 

Heating rate: a

40°C/min

b

20°C/min c

) (kW/m ) (kW/m ) (MJ/m ) (kJ/g) (m /kg) CO2

40°C/min

TABLE 5-17. CONE CALORIMETER RESULTS OF EXPOXY/TMP COMPOSITES 

wt% 

TMP 

tig 

(s

PHRR 

2

HRRav 

2

THR 

2

EHC SEA 

2

CO/ 

0 29 1324 235 42.6 23.7 655 0.030 

4 22 1294 217 39.6 21.5 577 0.054 

7.6* 21 494 120 22.9 14.7 520 0.119 

14.1 22 519 144 28.1 16.1 473 0.099 

* Results might not be accurate due to the irregular sample shape. 

5-31
0 200 30

0

400

600

800

00

1200

1400

 Epoxy

M

T

wt% TM

R (kW/m

me (s

100 0 400

200

10 4wt% T P

 7.6wt% MP

 11.4 P

H

R 2

)

Ti )

FIGURE 5-23. CONE HRR CURVES OF POXY MP C OSITE

5.3.6 Ignitability

EX /T OMP S

e ign n (tig an im rtant meter g ma amm

ny fa rs suc co ivity, at fl

 the ch to a r e of e al

mate l such um

l. ritica flux

. 

Time delay befor itio ) is po para characterizin terial fl ability.

It depends on ma cto h as thickness, density, thermal nduct and he ux [19].

In cone calorimeter tests, ange of tig ang xtern heat flux can produce valuable 

information for the ignitability of a ria as the critical heat flux, the minim incident

heat flux required for sustained piloted ignition of a materia The c l heat can be

obtained experim ntally by exposing a sample at decreasing incident heat fluxes until a flux is

found at which ignition time is infinitely long [19]. Another method is to plot 1/ (thin

materials) or 1

e

ig t (thic

ig t

/ " qe k materials) against external heat flux & based on the following 

equations [19 and 127].

(T −T ) ∞

( ) " "

e cr

ig

q& − q& ig t = ρcl (thin materials) (5-4) 

" 2

g ∞

4 q ) cr &

k − T = π (thick mat (5-5) 

where k is the thermal conductivity, ρ is th sity, e sp he s t ness, Tig

is the ign the external heat flux, is the

ritical heat flux, and kρc is the thermal inertia, which determines how fast the material responds

to a heat flux. 

For the thin samples, if the ignition temperature Tig is assumed to be the temperature at 

maximum mass loss rate, the thermal inertia and critical heat flux can be calculated from the 

erials)

e den c is th ecific at, l i he thick

2

( q

c(T ) t "

e

i

ig & −

ρ

ition temperature, T∞ is the ambient temperature, " qe & is " qcr &

c

5-32
slope and interception of plot 1/ versus . The results are listed in table 5-18 and shown in 

figure 5-24. 

TABLE 5-18. CRITICAL HEAT FLUX AND THERMAL PROPERTY CALCULATED 

FROM THE CONE CALORIMETER 

Polymers 

Critical Heat Flux 

(kW/m2) ρc (kJ/m3

-K) 

ig t " qe &

net

o

c

ext flame loss

o

c

c q

h

q q q

h

q& = χ ( & + & − & ) = χ & (5-6)

A-6133 V-0 15 1552 

Xydar M-345 22 2676 

PES 25 1720 

PSU 26 1792 

A-6135 HS 29 1005 

Xydar G-930 32 1226 

PPhS 35 1271

40 50 60 70 110

10

30

External heat flux (kW/m )

50

70

90

110

 PSU

 PPhS

 A-6135HS

 AFA-6133 V-0

 Xydar M-345

 Xydar G-930

 PES

1/tig (x10

3/s)

80 90 100

2

FIGURE 5-24. IGNITION TIME OF POLYMERS UNDER DIFFERENT EXTERNAL 

HE F

.3.7 Heat Release Rate

AT LUXES 

5 . 

iciency [128]:

Cone calorimeter data obtained over a range of external heat fluxes can also be used to obtain 

some other flammability parameters. Lyon found that the heat produced from combustion of a 

material in the presence of external flux qext & is a function of its chemical structure and

combustion eff

Lg Lg

5-33
Where qnet & is the net heat flux, q me & is heat flux from surface flame, qloss & is the heat loss due to

radiation and

fla

χ is the com

ffective h

 volatile

uel. T

convection, and bustion efficiency. The ical structure is

flect terms of the e eat of combustion and its heat of gasification per unit 

ma y

com unit m ss of . The heat of gasif cation, , is the energy required to

volatilize the unit m of the f verag during vaporization of

the fuel and does not include transient burning effect e rate data are 

plotted as a function of external heat heat rel e para

effect of chem

ects

er

ed in

bustion of

o h

i

e a

eas

g

a

ass 

Lg

e eff

s [128]. If the heat releas

flux, met

g

re c

ss of volatiles L [128]. The o hc represents the total amount of energy released b

he Lg represents th

the ,

o hc

L χ

180

, can be obtained 

from the slope of the curve [129] (figure 5-25). 

50 60 70 80 90 100

0

200

400

600

800

1000

1200

1400

1600

0 PSU

 PPhS

 A-6000

 A-6135 HS

 A-6133 V-0

 Xydar G-930

Peak heat release rate (kW/m2

)

External heat flux (kW/m2)

FIGURE 5-25. PEAK HEAT RELEASE RATE OF POLYMERS UNDER DIFFERENT 

EXTERNAL HEAT FLUXES 

Lyon also found that the intercept of the curve, HRR , is another flammability criterion that can 

be u

0

sed to predict the tendency to self-extinguish at zero external heat flux [129]. 

HRR0 

o o o

( q q ) L

h

q L

h ( q q q ) L

h

q flame loss

g

c

ext

g

c

ext flame loss

g

c

c & = χ & + & − & = χ & + χ & − &

Lyon found that in the absence of an external heat flux, there is a critical heat release rate at 

ame extinction, HRR* ≅100 kW/m2

. When HRR0 > HRR*, a flame will propagate; when

HRR0 < HRR*, a flame will extinguish. By using this approach, UL 94 and LOI test results can 

e well predicted. When HRR0 > 100 kW/m2, the material will be r

fl

b ated as HB in a UL 94 test; 

5-34
when H 0 < 100 kW/m2

, the m ial will be rated as V-0/1/2; when R0 is negative, there is

no ignition at all [129]. 

The heat release parameter (

g

o

c

L

h

χ ) and heat release rate at zero external heat flux (HRR0) of 

several materials are listed in table 5-19. It can be seen that the smaller the heat release 

parameter, the more ignition resistant the aterial is, as evidenced by UL 94 V-0 rating. Except 

for A-6000, there is a correlation between HRR0 and UL 94 rating. 

TABLE 5-19. MATERIAL FLAMMABILITY OBTAINED BY 

RR ater HR

m

CONE CALORIMETER DATA 

Materials g

o

c

L

h

χ HRR0

(kW/m2

) 

UL 94 

Rating 

Xydar G-930 0.88 58 V-0 

A-6133 V-0 2.64 69 V-0 

PPhS 2.9 96 V-0 

PSU 4.0 371 HB 

A-6135 HS 6.3 329 HB 

A-6000 17.7 -18 HB 

5.3.8 Correlation Between Different Flammability Tests. 

The applicability of the PCFC method to different materials is a very important issue. Because

complete oxidation is assumed in the high-temperature furnace of PCFC, it has been suspected 

whether the gas-phase flame-retardant effects of the halogenated additives can be achieved in the 

PCFC test. This question can be clarified by comparing the PCFC test with some standard realflam

he flammability of more than 20 kinds of materials including pure polymers and their fiberand the PCFC

alorimeter at a heating rate of 4.3°C/s to 930°C. The results from different methods are shown 

table 5-20 and figures 5-26 and 5-27, in which the O sults are based on the oxygen

epletion measurements. In figures 5-26 and 5-27, the straight lines are fitted only by the data 

from pure polymers. 

e combustion tests, such as the OSU and cone calorimeter tests. 

T

reinforced or flame-retarded composites is measured by the OSU calorimeter at an external heat 

flux of 35 kW/m2

, the cone calorimeter at an external heat flux of 50 kW/m2,

c

in SU re

d

5-35
TABLE 5-20. FLAMMABILITY MEASURED BY PCFC, OSU, AND 

CONE CALORIMETERS 

Peak Heat Release Rate 

Total Heat Released 

(kJ/g) 

Number Polymers

PCFC 

(J/g-K) 

Cone 

(kW/m2)

OSU 

(kW/m2) PCFC Cone OSU

1 Radel R-5000 171 260 173 13 11 7 

2 Ra  del A-300 165 357 203 12 11 6 

3 PEEK 450G 282 510 12 15 

4 Udel P-1700 336 573 288 17 18 12 

5 PPA A-1000 610 685 417 31 21 12 

6 PPA A-6000 540 844 411 33 24 14 

Xydar G-9  30

Xydar



PEEK 450G

AFA-61

7 Epoxy 1100 1324 27 23 

8 137 84 103 8 7 4 

9 M-345 120 105 179 6 5 5 

10 PEEK 450CA30 110 104 8 6 

11 L30 188 133 8 6 

12 45 V-0 210 181 287 10 5 8 

13 AFA-6133 V-0 270 191 306 13 6 10 

14 AF-1133 V-0 400 198 262 13 7 

15 AF-1145 V-0 440 222 11 5 

16 A-6145 HS 300 505 433 18 14 12

17 Epoxy/7.5% TMP 710 494 25 13 

18 A-1145 HS 350 612 17 12 

19 A-6135 HS 370 640 420 21 18 14 

20 A-1133 HS 410 657 21 15 9 

21 Epoxy/4% TMP 680 1294 26 21 

22 Epoxy/14.1% TMP 550 519 23 14 

*The OSU results are based on oxygen consumption. 

5-36
0 50 1 0 200 00 350 450

0

300

400

500

600

19

13

9

8

6

2 1

 y=1.28x, R=0.99

y (J/g.K) (PCFC)

HRR (kW SU)

 Pure polymers 5

 Polymer composites

00 15 250 3 400

100

200

16

12

4

H. R. Capacit

P /m ) (O 2

100 15 250 40

1

200

300

400

500

600

700

1

1

14

8

4

re polyme

mer co

84x, R=

PHRR (kW/m2) (Cone)

P /m2) (

600

1200

7

5

re polym

lymer c s

0.74x, R

ty (J/g.K) (PCFC)

FIGURE 5-26. CORRELATIONS OF PHRR BETWEEN DIFFERENT

FLAMMABILITY TESTS 

(The OSU results are based on oxygen consumption and the straight lines 

are fitted only by the data from pure polymers.) 

0 50 0 200 300 350 0 450

0

00

800

900

16

9

13 2

9

6

5

2

1

 Pu rs

 Poly mposites

 y=1. 0.96

HRR (kW OSU)

0 200 400 600 800 1000 1200 1400

0

200

800

1000

21

20

19

17

15

13

11 12

9,10

8

6

4

3

1 2

Pu ers

Po omposite

 y= =0.97

H.R. aci

PHRR (kW/m2) (Cone)

400

18 16

14

 cap

5-37
02468 10 12 14 16 18 20 22 24

0

5

10

15

20

25

30

35

7 21

20 19

22

17

16

18

14 13

10,11 8

15

12

9

6

5

4

3 2 1

 Pure polymers

 Polymer composites

 y=1.19x, R=0.92

Total heat (kJ/g) (PCFC)

Total heat (kJ/g) (Cone)

0 2 4 6 8 10 12 14 16

0

4

8

12

16

20

24

16

19

14

13

9 12

8

6

5

4

2 1

 Pure polymers

 Polymer composites

 y=1.67x, R=0.99

5 min. heat released (kJ/g) (OSU)

Total heat released (kJ/g) (Cone)

0 2 4 6 8 10 12 14 16

0

5

10

15

20

25

30

35

19

16

14 13

12

9

8

6

5

4

1 2

 Pure polymer

 Polymer composites

 y=2.1x, R=0.89

5 min. Heat released (kJ/g) (OSU)

Total heat released (kJ/g) (PCFC)

FIG N 

DIFFE STS 

URE 5-27. CORRELATIONS OF TOTAL HEAT RELEASED BETWEE

RENT FLAMMABILITY TE

(The OSU results are based on oxygen consumption and the straight lines 

are fitted only by the data from pure polymers.) 

5-38
Previous FAA research shows that there is good correlation between the cone calorimeter and the 

PCFC methods for pure polymers. According to the results, relatively good correlations between 

different methods are also observed for pure polymers. However, for the composites with inert 

fillers or flame-retardant additives, the OSU and cone calorimeter tests are the better evaluation

methods. This is because the OSU and cone calorimeter tests are real flame-combustion tests. 

Therefore, the halogenated additives can achieve the inefficient gas-phase combustion and 

reduce the heat released. The heat feeding back to the polymer surface will then be reduced, and

the decomposition of the polymers will be slowed down thereafter. However, as mentioned

before, the PCFC method is not a direct flame-combustion test, the pyrolysis and combustion 

processes are totally separated, and the combustion in the furnace is complete oxidation. As a 

result, the effects of the halogenated additives in the gas phase cannot be achieved and the 

influence of the heat and mass transfer processes in a real fire are not observed. However, the 

PCFC method stresses flammability more as a material property. The results are greatly 

dependent on the chemical structure and composition of materials. Therefore, it is still a very 

convenient screening tool for newly synthesized polymers without any additives. 

The materials studied were (1) Poly(phenyl sulfone) (Radel R-5000), (2) Poly(ether sulfone) 

(Radel A-300), (3) PEEK 450G (Victrex PEEK 450G), (4) Polysulfone (Udel P-1700), (5) 

PPA A-1000 (Amodel PPA), (6) PPA A-6000 (Amodel PPA), (7) Epoxy, (8) Xydar G-930, 

(9) Xydar M-345, (10) PEEK CA-30 (Victrex PEEK 450CA-30), (11) PEEK GL-30 

(Victrex PEEK 450GL-30), (12) AFA-6145 V-0 (Amodel PPA), (13) AFA-6133 V-0 

(Amodel PPA), (14) AF-1133 V-0 (Amodel PPA), (15) AF-1145 V-0 (Amodel PPA), (16) 

A-6145 HS (Amodel PPA), (17) Epoxy/7.5 wt% TMP (trimethoxy-phosphate), (18) A-1145 HS

(Amodel PPA), (19) A-6135 HS (Amodel PPA), (20) A-1133 HS (Amodel PPA), (21) 

Epoxy/4 wt% TMP, and (22) Epoxy/14.1 wt% TMP. Please refer to table 5-1 and figure 5-20 for 

detailed information about the structure and composition of each material. 

5.4 DISCUSSION. 

Flammability is determined by the physical and chemical characteristics of the materials. Inert 

fillers can reduce the flammability mainly by the mass-dilution effect and promoting the char

formation. However, the addition of inert fillers can also change the physical properties of the 

materials such as thermal conductivity, density, and heat capacity that will affect the ignition and

burning characteristics of the exposed surface. Therefore, the flame-retardant effect of the inert 

fillers in the real flaming-combustion OSU and cone calorimeter tests is usually not as dramatic 

as in the nonflaming PCFC test. If halogenated flame retardants or antimony compounds are 

used, the flammability can be greatly reduced due to the inefficient combustion in the gas phase. 

The only disadvantage is that the thermal stability of the materials will be decreased and a great 

deal of corrosive smoke will be generated. As to the instrumentation, because different methods 

have different experimental setups and are operated in different ways, the results from one

method cannot be directly related to the other. It was found that only pure polymers have 

relatively good correlations between different methods. Therefore, different types of materials 

require s more 

sensitive to the chemical s s; therefore, it is a good

different test methods to ensure valid and realistic results. The PCFC method i

tructure and composition of the material

5-39
screening tool for the pure polymers without any additives or inert fillers. However, the OSU 

and cone calorimeter tests are the better flammability tests for composite materials because these

two methods also include some physical processes, which are much more representative of the 

real fire conditions. 

5-40
6. STRUCTURE-COMPOSITION-FLAMMABILITY RELATIONSHIPS OF POLYMERS.

6.1 INTRODUCTION. 

A great deal of research has been done on measuring the flammability of polymers. 

Systematically relating polymer structure and composition to their flammability is, however,

more important for materials design and evaluation. 

It was found that the thermal stability depends on the structure of repeating units and, in 

particular, on the weakest bonds present in this structure [7]. C-C bonds are particularly resistant 

to homolytic scission relative to other bonds between identical atoms (except H-H bonds) [130]. 

C-H, C-O, C-F, and C-B bonds are stronger than C-C bonds. Aromaticity strengthens C-C bonds

and the presence of electronegative atoms (other than fluorine) weakens them. Thus, when 

aromatic groups or fluorine atoms are introduced into polymers, their thermal stability will 

increase [7]. 

Quantitative structure-property relations are of interest. Some research had been done to 

estimate the char yield, heat of combustion, or thermal decomposition temperature from the 

chemical structure by using molar group additivity principles [67 and 73]. 

In this section, the different factors that affect polymer flammability were studied in detail, such 

as chemical structures, molecular weight, free radicals in the polymer system, and composition 

of copolymers and blends. The goal is to establish the structure-composition-flammability

relationships of polymers and to help guide the development of new fire-resistant polymers. 

6.2 EXPERIMENTAL.

6.2.1 Materials. 

The materials evaluated were obtained from different sources. The specific detailed information

is provided in each section. All samples were dried at proper temperatures under vacuum for 

about 24 hours before measurements. 

6.2.2 Characterization.

The experimental conditions for TGA, STA, pyrolysis GC/MS, PCFC, OSU calorimeter, and 

cone calorimeter tests were the same as described in previous sections. 

6.3 CHEMICAL STRUCTURE.

6.3.1 Main Chain—Polysulfones. 

Aromatic polysulfones possess considerable thermal stability and good chemical resistance [6].

They are among the most fire-resistant, non-halogen-containing thermoplastic polymers. Their 

other properties such as high-heat deflection temperature, excellent toughness, and dimension 

stability allow them to be used in the electrical, automotive, and aircraft industries where a 

special combination of mechanical, thermal, or fire resistance are required [6]. 

6-1
In this section, three kinds of polysulfones supplied by BP Amoco Polymers Inc. (now Solvay 

Advanced Polymers, L.L.C.) were used to study how the aromaticity of polymer main chain 

affects its flammability. Their structures are listed in figure 6-1. 

C

CH3

CH3

O S

O

O

O

n

S

O

O

O S

O

O

O

n

O S

O

O n

Poly(phenylsulfone) O

(PPhS) Radel R-5000 

Poly(ethersulfone) (PES)

Radel A-300 

BPA-polysulfone (PSU)

Udel P-1700 

FIGURE 6-1. CHEMICAL STRUCTURES OF POLYSULFONES 

6.3.1.1 Thermal Decomposition Processes.

The thermal decomposition processes of three kinds of polysulfones, BPA-polysulfone (PSU), 

polyethersulfone (PES), and polyphenylsulfone (PPhS), are shown in figure 6-2. It can be seen 

that all these polysulfones decompose in a single step under N2. They all have relatively high 

thermal stability and char yields due to their aromatic structures in the main chain. They start to 

decompose around 450°C, then after a sharp weight loss, leave more than 30% residue at 

1000°C. By replacing the flexible BPA units in PSU with more rigid phenyl or biphenyl units in 

PES or PPhS, the thermal stability and char yields increase significantly. The reduction in the 

mass loss rates indicates that the decomposition rates of PES and PPhS are also slowed by the 

presence of more aromatic rings. 

0 200 400 600 800 1000

-40

-20

0

20

40

60

80

100

Temperature (oC)

Weight (

%)

 PSU

 PES

 PPhS

0

10

20

30

40

Deriv. of Weight (%/min)

FIGURE 6-2. THERMOGRAVIMETRIC ANALYSIS AND DTG CURVES OF 

POLYSULFONES IN N2

6-2
However, all these polysulfones decompose in two distinct steps in air (figure 6-3). The first

step is the same as in N2, starting and ending at almost the same temperatures and losing the 

same amount of weight. The second step leads to the complete burning of the polymers (no 

residue left). It is believed that the first step is mainly due to the chain scission reactions and the

release of volatiles, while the second stage is mainly due to the oxidation of the carbonaceous

char formed at the end of the first stage. 

0 200 400 600 800 1000

-100

-50

0

50

100

Temperature (oC)

Weight (%)

 PSU

 PES

 PPhS

0

5

10

15

20

25

30

Deriv. of Weight (%/min)

FIGURE 6-3. THE TGA AND DTG CURVES OF POLYSULFONES IN AIR 

High-temperature DSC data of polysulfones are shown in figure 6-4 and in table 6-1. It can be 

seen that during decomposition in N2, all the polysulfones exhibit two endothermic peaks related 

to different chemical and physical processes. The first peak corresponds to the major part of the 

weight loss, which might be due to the combination of bond dissociation, formation, and 

vaporization of the volatiles. The second peak occurs at high temperatures and corresponds to a 

narrow temperature range, which might be due to the char-forming process. Compared with 

PSU, PES and PPhS absorb more heat during decomposition, which might increase the energy 

needed to sustain the combustion and reduce flammability. 

200 400 600 800

PPhS

PES

PSU

Exothermic

Temperature (oC)

FIGURE 6-4. HIGH-TEMPERATURE DSC CURVES OF POLYSULFONES 

6-3
TABLE 6-1. THERMAL DECOMPOSITION PROPERTIES OF POLYSULFONES 

In N2 In air

Polymer 

T99%/ 

T95%a 

(°C) 

Tmax

b

(°C) 

PMLRc

(x103

/s)

Chard

(%) 

∆He

(J/g) 

T99%/ 

T95%

f

(°C) 

T2

g

(°C) 

Tmax

(°C) 

PMLR 

(x103

/s) 

PSU 482

502 

526 3.33 31 61

28 

462 

497 

588 528 2.42

PES 471

517 

570 2.13 37 120

38 

470 

511 

610 572 2.15

PPhS 504

540 

579 1.77 45 123

25 

488 

531 

638 651 1.55

a

 Temperatures at 1% and 5% weight loss 

b

 Temperatures at maximum mass loss rate c

 maximum (peak) mass loss rate

d

 Residual left at 930° e Heat of decomposition f Onset of decompensation temperature of the second stage 

TGA measurements of polysulfones were also carried out at different heating rates to determine 

the global thermal decomposition activation energies. It can be seen that with the increase of

heating rates, the onset decomposition temperatures and mass loss rates of the polysulfones 

increase, but the char yields do not change significantly (figure 6-5). The increase of the onset 

decomposition temperature does not mean that the thermal stability of the polymers has 

increased. It is mainly due to a kinetics effect, i.e., the thermal response of the polymers is

delayed at fast heating rates. 

The relatively simple Kissinger method (equation 6-1) was used to determine the activation 

energies [131] 

 (6-1) a a m

n ln( / Tm ) = ln( nRAWm / E ) − E / RT 2 −1 φ

where φ is the heating rate in the TGA experiment, Tm is the temperature at the maximum rate of 

weight loss, R is the gas constant, Ea is the activation energy, A is the pre-exponential factor, Wm

is the weight of the sample at the maximum rate of weight loss, and n is the apparent order of the 

reaction with respect to the sample weight. The value of Ea can be determined from a plot of 

ln( / Tm )vs 1/T 2 φ m at various heating rates. The particular advantage of this method is that it

requires only the temperature at the maximum rate of weight loss to determine the value of Ea

and one need not assume the order of the reaction [132]. The disadvantage of this method is that 

it is sometimes difficult to determine the maximum rate of weight loss accurately. 

A plot of ln( / Tm )vs 1/T 2 φ m of polysulfones is shown in figure 6-6. It can be seen that three 

reasonable straight lines were obtained. The activation energies were calculated from the slopes

of these straight lines (table 6-2). It was found that PES and PPhS have higher decomposition 

activation energies than PSU, which agrees with their higher thermal stability. 

6-4
400 500 600 700

-40

-20

0

20

40

60

80

100

Temperature (oC)

Weight (

%)

Heating rate (oC/min)

 2

 3

 4

 5

 10

 20

0

20

40

60

80

Deriv. of Weight (%/min)

(a) 

400 500 600 700

-40

-20

0

20

40

60

80

100

Temperature (oC)

Weight (

%)

Heating rate (oC/min)

 2

 3

 4

 5

 7

 10

 20

0

10

20

30

40

50

60

Deriv. of Weight (%/min)

(b) 

400 500 600 700

-20

0

20

40

60

80

100

Temperature (oC)

Weight (

%)

Heating rate (oC/min)

 2

 3

 4

 5

 7

 9

 10

0

5

10

15

20

25

30

Deriv. of Weight (%/min)

(c) 

FIGURE 6-5. THE TGA AND DTG CURVES OF POLYSULFONES AT DIFFERENT 

HEATING RATES (a) PSU, (b) PES, AND (c) PPhS 

6-5
1.15 1.20 1.25 1.30

-17.5

-17.0

-16.5

-16.0

-15.5

-15.0

-14.5

PPhS

PES

PSU

ln(φ/Tm

2

)

103/Tm(K-1)

FIGURE 6-6. KISSINGER PLOT OF POLYSULFONES DECOMPOSED IN N2

TABLE 6-2. BOND DISSOCIATION ENERGIES AND ACTIVATION 

ENERGIES OF POLYSULFONES 

The bond dissociation energies of these polysulfones can be calculated by using B3LYP [74 and 

75] density-functional method with a standard polarized split-valence 6-31G(d) [76] basis set 

from the Gaussian 98 package of programs [77] (table 6-2). It can be seen that the weakest bond 

is PSU is the C-CH3 bond in isopropyl groups, while the C-S bond in the sulfone linkage is the 

weakest in PES and PPhS. In addition, activation energies measured by TGA data seem very 

close to the calculated weakest bond dissociation energies when calculation errors are 

considered. This result indicates that the thermal decomposition of these polysulfones is

consistent with initiation by the rupture of the weakest bond. 

6.3.1.2 Decomposition Volatiles.

It was found that the major decomposition volatiles from these polysulfones are SO2, CO2, CO, 

phenol, and a series of aromatic ethers derived from the polymer main chain (figure 6-7). The 

volatiles from PPhS contain more biphenyl structures than PES, and the decomposition products 

6-6
from PSU contain more flammable aliphatic groups due to the isopropyl groups in the polymer, 

which is also one of the reasons for its high flammability. 

OH

OH

OH

O

O

O

C2H5

O

OH

O

O

CO2, CO

SO2

(a) 

SO2

CO2, CO

OH

O

O

O

O

O

and 

(b) 

SO2

CO2, CO

OH

O

O

O

O

OH

O

OH

(c)

FIGURE 6-7. PYROLYSIS GC/MS TRACES OF POLYSULFONES (a) PSU, 

(b) PES, AND (c) PPhS 

6-7
6.3.1.3 Flammability Measured by PCFC.

The PCFC results are shown in table 6-3, from which one can see that the rigid PES and PPhS 

are more fire-resistant than PSU. The order of the flammability is PSU > PES ≥ PPhS. The heat 

release capacities and the total heats of combustion of PES and PPhS are only half of those of 

PSU. Their low mass loss rate and high char yields are part of the reasons for their low 

flammability. According to pyrolysis GC/MS results, the major decomposition products of all 

three polysulfones at the temperatures of maximum mass loss rates are SO2 and phenol. 

However, PSU also releases a high molecular weight flammable compound,

C6H5C(CH3)2C6H4OH. Considering this factor and its high mass loss rate, the high heat release

capacity of PSU is easy to understand. 

TABLE 6-3. FLAMMABILITY OF POLYSULFONES MEASURED BY PCFC 

Polymers 

H.R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

Char 

(%) 

Cov 

(%)a

PSU 336 17 31 2.5

PES 171 13 37 7.7

PPhS 165 12 45 4.8

a Coefficient variation of heat release capacity

6.3.1.4 Flammability Measured by the OSU Calorimeter. 

The flammability of these polysulfones, measured by the OSU calorimeter, also decreases in the

order of PSU > PES ≥ PPhS (table 6-4). Because some of the melt from PSU drips down to the 

bottom of the furnace during burning, its measured flammability was underestimated. 

TABLE 6-4. FLAMMABILITY OF POLYSULFONES MEASURED BY 

THE OSU CALORIMETER 

Method Parameters PSU PES PPhS

PHRR (kW/m

2

) 135 98 86

2-min HR (kW.min/m2 Thermopile ) 73 42 18

5-min HR (kW.min/m

2

) 317 199 211

PHRR (kW/m

2

) 288 203 173

2-min HR (kW.min/m

2

) 169 85 43 O2

consumption 

5-min HR (kW.min/m2

) 473 288 312

Char (%) 39 52 55 

According to the requirements in FAA Amendment 25-61(Code of Federal Regulations Part 

25.853 [a-1]), if a material has less than 65kW/m2

 as the peak of heat release rate and less than

65 kW⋅min/m

2

 as the 2-minute total heat release for the thermopile measurement, the material is

qualified as an aircraft cabin material. According to table 6-4, PPhS is a promising material that 

6-8
could easily pass the FAA requirements after some composition modification, perhaps with

additives. The high thermal stability and low mass loss rate of PPhS play an important role in its

low flammability. 

The burning processes of three polysulfones are shown in the OSU HRR curves (figure 6-8). It 

can be seen that the initial burning time of the polymers is primarily determined by their thermal 

stability. PPhS has a more rigid structure, so it is more thermally stable and has a long time

delay before burning. Furthermore, it burns more slowly and produces more char. 

0 1 2 3 4 5

0

20

40

60

80

100

120

140

160

PES

PPhS

PSU

HRR (kW/

m2

)

Time (s)

FIGURE 6-8. THE OSU HRR CURVES OF POLYSULFONES 

MEASURED BY THERMOPILE 

It was found that char yield measured at the end of the 5-minute burning in the OSU tests is 

higher than from the TGA and PCFC results, which indicates that the burning process of these 

polysulfones was not yet complete at the end of 5 minutes. Therefore, the 5-min HR measured 

by the OSU test is less than the total heat released measured by PCFC. In addition, the char of 

PPhS can remain intact after the test, while PSU and PES only form fragmented chars due to

dripping or sagging problems during combustion. All the chars formed are porous because a 

large amount of SO2 is released during decomposition. 

6.3.1.5 Flammability Measured by the Cone Calorimeter.

The cone calorimeter results include ignition time, heat release rate, and smoke evolution at 

different heat fluxes (table 6-5). As expected, increasing heat flux can lead to a reduction in tig, 

an increase in heat release rate with generally shorter times of burning, and an increase in mass

loss rate. The decrease of CO/CO2 ratios indicates that the combustion tends to be complete at 

high heat flux. However, the total heat released and the effective heat of combustion are not 

substantially different over the heat flux range tested. 

The order of the flammability from the cone calorimeter test is the same as from the OSU results. 

Compared with PSU, PES and PPhS have a significantly lower PHRR, HRRav, and THR. In

addition, the low effective heats of combustion of PES and PPhS suggest the release of low fuel

6-9
value volatiles during decomposition. Their increased char yields might also give a good 

radiation shield protection to the underlying materials. 

TABLE 6-5. FLAMMABILITY OF POLYSULFONES MEASURED BY THE 

CONE CALORIMETER 

Polymer 

Heat Fluxa

(kW/m2

) 

tig

b

(s) 

PHRRc

(kW/m2

) 

HRRavd

(kW/m2

) 

THRe

(MJ/m2

) 

MLRf

(g/m2

.s) 

50 57 598 183 43.6 8.18

PSU 75 30 671 198 42.1 10.10

100 19 738 203 40.0 12.01

50 61 381 119 31.7 6.78

PES 75 29 379 132 29.4 9.92

100 20 561 153 34.8 10.61

50 71 267 108 26.9 5.88

PPhS 75 28 284 127 28.6 8.17

100 17 407 134 29.2 8.39

Polymer 

Heat Flux 

(kW/m

2

) 

EHC 

(kJ/g) g

SEA 

(m2/kg) h CO/CO2

i

50 19.8 581.3 0.149

PSU 75 19.8 685.9 0.051

100 19.1 784.0 0.024

50 15.4 419.9 0.144

PES 75 13.8 551.0 0.041

100 14.6 523.5 0.018

50 15.7 721.0 0.135

PPhS 75 16.4 890.1 0.048

100 15.1 784.8 0.026

a External heat flux 

b Time to ignition using a pilot spark c Peak heat release rate 

d Mean values from tig to 180s after e Total heat released f Average mass loss rate g Effective heat of combustion calculated from total heat released and overall mass loss h Smoke specific extinction area i Ratio of production of CO to CO2 during combustion 

The cone heat release rate curves of these polysulfones are shown in figure 6-9. Generally, at the 

beginning of the test, the samples were increasing in temperature and starting to produce 

pyrolysis gases. At a certain point, ignition occurred and flaming combustion started. For 

6-10
thermally thin thermoplastic samples, the heat release rate rose quickly to a peak heat release rate 

after ignition and then decreased as the fuel in the sample was consumed [133 and 19]. It can be 

seen that although PSU and PES showed one sharp burning peak, the heat release peak of PPhS 

is much broader. The fact that heat release rates of all three polysulfones did not return to zero at 

the end of the tests might be attributed to the smoldering burning under the char. 

0 100 200 300 400 500

-50

0

50

100

150

200

250

300

350

400

450

500

550

600

PPhS

PES

PSU

HRR (kW/m2

)

Time (s)

FIGURE 6-9. CONE HRR CURVES OF POLYSULFONES 

Based on all the experimental results, it can be seen that the main-chain structure can greatly 

affect the thermal decomposition and flammability of the polymers. Increasing the chain 

aromaticity cannot only increase the thermal stability and char yield, but also, it can decrease the 

flammability by reducing the release rate and amount of flammable pyrolysis gases. By 

changing the structure of PSU to more rigid PES and PPhS, the polymers become much more

fire resistant. 

It was also found that the order of the flammability of these polysulfones measured by PCFC, 

OSU, and cone calorimeters is consistent with each other, even though experimental conditions 

and calculation procedures in these three tests are very different. This result indicates that for 

pure polymers, the chemical structure is the predominant factor that can determine the

flammability of polymers. 

6.3.2 Semiorganic Network Structure—Polycarbynes and Polysilynes.

Semiorganic polymers have inorganic chains (such as silicons) framed by organic substituents or

organic backbones surrounded by inorganic substituents. In this part, polycarbynes and 

polysilynes with random carbon or silicon network structures were studied. These polymers 

were provided by Prof. Patricia Bianconi [134] at the University of Massachusetts, Amherst. It

is believed that the polymers consist of sp3

-hybridized C or Si atoms bonded via C-C or Si-Si 

single bonds to three other backbone atoms and one substituent [134]. This unique backbone 

structure will confer novel properties; for example, pyrolytic conversion to diamond or diamondlike carbon at atmospheric pressures. The schematic structures are shown in figure 6-10. 

6-11
R

R

H

H

R R

R R R

R

R

R R

R R

R

R R

R

R

R

R

R

R R

R

H

H

H H H

H

H

H

H

H

Polymers 

Poly(carboxyl 

carbyne) 

Poly(hydrocarbyne) Poly(phenyl 

silyne) 

Poly(methyl 

silyne) 

Central atom C C Si Si 

R COOH H C6H5 CH3

FIGURE 6-10. SCHEMATIC STRUCTURES OF POLYCARBYNES 

AND POLYSILYNES [134] 

6.3.2.1 Thermal Decomposition Processes.

The thermal decomposition processes of two polycarbynes (poly(hydrocarbyne) and 

poly(carboxyl carbyne)) are shown in figure 6-11. 

0 200 400 600 800 1000

0

20

40

60

80

100

Temperature (oC)

Weight (

%)

0

5

10

15

20

Deriv. of Weight (%/min)

 poly(hydro carbyne)

 poly(carboxyl carbyne)

FIGURE 6-11. THE TGA AND DTG CURVES OF POLYCARBYNES

It can be seen that they all have relatively low thermal stability, starting to decompose around 

150°C. After 500°C, the thermal decomposition of poly(carboxyl carbyne) reaches a plateau, but 

then it begins to lose weight dramatically after 800°C, which might be due to the extensive

breakdown of the main network structure. However, poly(hydrocarbyne) loses weight 

continuously until 900°C, leaving about 20% char at 1000°C.

6-12
Figure 6-12 shows the thermal decomposition processes of two polysilynes (poly(methyl silyne) 

and poly(phenyl silyne)). Similar to the polycarbynes, these polysilynes also have very low 

thermal stability. Above 600°C, the thermal decomposition processes of these polysilynes reach 

a plateau, leaving more than 60% char. Compared with poly(methyl silyne), poly(phenyl silyne) 

decomposes at a much slower rate and produces more char. 

0 200 400 600 800 1000

0

20

40

60

80

100

Temperature (oC)

Weight (%)

0

1

2

3

4

5

 poly(methyl silyne)

 poly(phenyl silyne)

Deriv. of Weight (%/min)

FIGURE 6-12. THE TGA AND DTG CURVES OF POLYSILYNES 

6.3.2.2 Thermal Decomposition Products.

The thermal decomposition products of poly(carboxyl carbyne) are small gas molecules with 

very low flammability, i.e., CO2, O2, CO, and H2O. Poly(methyl silyne) releases a series of 

siloxanes, which might be due to the oxidation. Poly(phenyl silyne) releases a series of lowflammable, phenyl-substituted silanes. However, poly(hydrocarbyne) releases a series of

flammable alkenes and aromatic hydrocarbons and phenolics. 

6.3.2.3 Flammability.

The flammability of polycarbynes and polysilynes is shown in table 6-6. It can be seen that all 

these polymers have very low flammability. Poly(carboxyl carbyne) has the lowest heat release 

rate and total heat released, which is due to the release of volatiles with low flammability. 

However, its flammability might dramatically increase above 800°C due to its suddenly 

increased mass loss rate. The flammability of two polysilynes mainly comes from the methyl or 

phenyl side groups. The relatively high mass loss rate and flammable hydrocarbon volatiles are 

the major reasons for the high flammability of poly(hydrocarbyne). 

6-13
TABLE 6-6. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

POLYCARBYNES AND POLYSILYNES 

Polymers 

H.R. 

Capacity

(J/g-K) 

Total 

Heat 

(kJ/g) 

Char 

Yield 

(%) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

Tonset*

(°C) 

Poly(carboxyl carbyne) (C, -COOH) 11 3 55 144 

Poly(phenyl silyne) (Si, -C6H5) 32 13 77 0.12 425 140

Poly(methyl silyne) (Si, -CH3) 92 15 64 0.34 447 126

Poly(hydrocarbyne) (C, -H) 107 19 23 0.58 423 149 

*Onset decomposition temperature 

6.3.3 Substituents.

6.3.3.1 Size of Substituents—Polymethacrylates. 

Three polymethacrylates (poly(ethyl methacrylate), poly(isobutyl methacrylate) and poly(benzyl 

methacrylate)) have been used to study the effects of the steric substituents on polymer

flammability. The polymers were provided by Javid Rzayev [135] at the University of 

Massachusetts, Amherst. Their chemical structures are shown in figure 6-13. 

R

O

H3CO

n

 R= ethyl, iso-butyl, benzyl 

FIGURE 6-13. CHEMICAL STRUCTURES OF POLYMETHACRYLATES 

The thermal decomposition processes of these polymethacrylates are shown in figure 6-14. It 

can be seen that both poly(isobutyl methacrylate) and poly(benzyl methacrylate) have lower 

thermal stability than poly(ethyl methacrylate). The multistep decomposition in these two

polymers is also different from the single step in poly(ethyl methacrylate). The decomposition at

low temperatures is mainly caused by the cleavage of the bulky side groups. Their broad 

decomposition leads to a dramatic decrease in the mass loss rates. 

The flammability and thermal decomposition of these polymethacrylates are summarized in 

table 6-7. 

The introduction of bulky and rigid benzyl side groups makes the poly(benzyl methacrylate) 

chain more rigid, which leads to its high glass transition temperature. Its low heat release rate is

mainly due to its broad decomposition range and low maximum mass loss rate. Although the 

maximum mass loss rate of poly(isobutyl methacrylate) is also significantly lower than 

poly(ethyl methacrylate), their heat release capacities are almost the same. This is because 

poly(isobutyl methacrylate) has a relatively higher concentration of carbon and hydrogen (fuel 

sources), and the volatiles produced have higher heat of combustion. In addition, all three 

6-14
polymethacrylates produce no char. Therefore, the total heat of combustion will completely 

depend on the heat of combustion of the volatiles they released. As a result, the total heat

released of poly(isobutyl methacrylate) is the highest due to its high fuel value volatiles. 

0 50 100 150 200 250 300 350 400 450 500

-100

-50

0

50

100

Temperature (oC)

Weight (

%)

 ethyl

 iso-butyl

 benzyl

0

10

20

30

40

50

60

D

eriv. of W

eight (%/min)

FIGURE 6-14. THE TGA AND DTG CURVES OF POLYMETHACRYLATES 

TABLE 6-7. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

POLYMETHACRYLATES 

R 

H.R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

Max. Mass Loss Rate 

(x103

/s) 

Tmax

(°C) 

T95%

(°C) 

Tg

(°C) 

Ethyl 840 26 4.5 335 295 71

Iso-butyl 890 29 2.7 323 224 63

Benzyl 240 28 1.5 273 238 122

From pyrolysis GC/MS results (figure 6-15), it can be seen that the thermal decomposition 

mechanisms can be changed by the size of the substituents. The major decomposition product of 

poly(ethyl methacrylate) is the monomer, which indicates an unzipping mechanism. However,

although monomer is still one of the major decomposition products for poly(isobutyl 

methacrylate) and poly(benzyl methacrylate), some other volatiles such as isobutylene, styrene, 

and fragmented dimers have also been detected. Therefore, the thermal decomposition 

mechanisms of these two polymers are a combination of unzipping, cleavage of the side groups, 

and random chain scission. 

6-15
C2H5 (a) 

O

H3CO

O

H3CO

O

H3CO

O

H3CO (b) 

O O

O O

OCH3

O

O

OCH3

O

OCH3

O

OCH3

(c) 

FIGURE 6-15. THERMAL DECOMPOSITION PRODUCTS OF POLYMETHACRYLATES 

(a) ETHYL METHACRYLATE, (b) ISOBUTYL METHACRYLATE, 

AND (c) BENZYL METHACRYLATE 

6.3.3.2 Cyano-Substituted Aromatic Polymers.

A dramatic flammability reduction caused by cyano groups has been observed in a series of

cyano-substituted aromatic polymers that were synthesized by Terry Hobbs [136] at the 

University of Massachusetts, Amherst. The chemical structures of these polymers are shown in

figure 6-16. 

6-16
O NH C

O

C

O

NH NH

HN CN x

50-x 50

PA-CN(X) 

(X=10, 25, 35, 50) 

N C N H CH

CN

N N

95 5

Poly(azomethine) 

FIGURE 6-16. CHEMICAL STRUCTURES OF CYANO-SUBSTITUTED POLYMERS 

The TGA and DTG curves of PA-CN(X) series are shown in figure 6-17. It can be seen that 

with the increased amount of CN-substituted diamine units, the thermal stability and char yield

all increase correspondingly. In addition, the thermal decomposition processes are changed from 

a sharp single peak with a small shoulder into two peaks, then merging into another single peak, 

because polymer structures are changed from copolymers to a homopolymer (PA-CN(50)). 

0 200 400 600 800 1000

0

20

40

60

80

100

 PA-CN(10)

 PA-CN(25)

 PA-CN(35)

 PA-CN(50)

Temperature (oC)

Weight (%)

0

2

4

6

8

10

12

14

16

Deriv. weight (%/min)

FIGURE 6-17. THE TGA AND DTG CURVES OF CYANO-SUBSTITUTED POLYAMIDES 

More interestingly, PA-CN(25) and PA-CN(50) have similar backbone structures to Technora

and Kevlar, respectively. The only difference between them is that PA-CN(X) polymers 

contain CN side groups. Comparing their decomposition processes, the introduction of a CN 

group can greatly increase the char yield and reduce the mass loss rate (figure 6-18). However, 

the thermal stability is slightly reduced. It was also found that if the C=N bond is incorporated in 

the polymer main chain to form a highly conjugated system, such as poly(azomethine), the char 

yield can be dramatically increased and the decomposition rate can be dramatically decreased. 

The heat events during decomposition are more complicated (figure 6-19). PA-CN(X) 

polyamides show a endothermic decomposition peak, but poly(azomethine) shows an obvious 

exothermic peak, which might be due to the cross-linking reactions during decomposition. 

6-17
0 200 400 600 800 1000

0

20

40

60

80

100

 PA-CN(25)

 Technora

Temperature (OC)

Weight (%)

0

5

10

15

20

Deriv. Weight (%/min)

0 200 400 600 800 1000

0

20

40

60

80

100

 Kevlar

 PA-CN(50)

 poly(azomethine)

Temperature (oC)

Weight (%)

0

4

8

12

16

20

24

Deriv. Weight (%/min)

FIGURE 6-18. THE TGA AND DTG CURVES OF PA-CN(X) AND POLY(AZOMETHINE) 

COMPARED WITH TECHNORA AND KEVLAR

200 400 600 800

Azomethine

PA-CN(50)

PA-CN(35)

Heat flow (Exo up)

Temperature (oC)

FIGURE 6-19. HIGH-TEMPERATURE DSC CURVES OF 

CN-SUBSTITUTED POLYMERS 

According to pyrolysis GC/MS results (figure 6-20), with the increased amount of CN side 

groups, lower amounts of benzene and flammable high-molecular-weight volatiles are released. 

However, more benzonitrile and benzodinitrile are released. The major decomposition products 

of poly(azomethine) are CO2, CO, and a series of aromatic compounds with CN groups. 

6-18
CO2, CO 

NH3, HCN 

NH2

CN

OH

COOH

O

NH2

O

NH2

NH2

CO

NH CN

CN

(a) 

NH2

CN

OH

COOH

OH

CN

O

NH2

O

NH2

NH2

(b) 

CO2, CO 

NH3, HCN 

(c) 

CO2, CO 

NH3, HCN 

NH2

CN

OH

COOH CN

CN

(d) 

CO2, CO 

NH3, HCN 

NH2

CN

CN

CN

CN

NH2

CN

FIGURE 6-20. PYROLYSIS GC/MS TRACES OF PA-CN (X) AND POLY(AZOMETHINE) 

(a) TECHNORA, (b) PA-CN (25), (c) PA-CN (50), AND (d) POLY(AZOMETHINE) 

6-19
Table 6-8 summarizes the flammability and thermal decomposition of PA-CN(X) and

poly(azomethine), which are compared with Technora and Kevlar. It was found that with the 

introduction of more CN groups, the heat release capacity and total heat released all decrease, 

which indicates the CN group is an efficient flame-retardant unit. In particular, the introduction 

of C=N groups in the polymer main chain, such as poly(azomethine), can dramatically reduce the

flammability. It was also found that the total heat released changes almost linearly with the 

molar fraction of CN-substituted diamine, while the heat release capacity is synergistically

reduced by only a very small amount of CN groups. 

TABLE 6-8. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

PA-CN(X) POLYAMIDES 

X 

H.R. 

Capacity 

(J/g-K) 

Total 

Heat 

(kJ/g) 

Char 

Yield 

(%) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

Tonset 

(°C) 

10 110 15 43 1.20 469 441

25 87 14 51 0.80 485 460

35 57 11 53 0.54 546 479

50 55 9 58 0.77 549 512

Technora 131 15 42 1.71 502 487

Kevlar 292 15 39 1.96 572 539

Poly(azomethine) 37 9 78 0.11 563 522

6.3.4 Flame-Retardant Comonomers.

6.3.4.1 Silicon-Based Comonomer—Polyethylene/Polyhedral Oligomeric Silsesquioxanes 

Hybrid. 

The effects of a silicon-based comonomer (polyhedral oligomeric silsesquioxanes (POSS) 

monomer containing seven cyclopentyl and one norbornylene group) on polymer flammability 

were studied by using polyethylene POSS hybrid copolymers. The copolymers with a wide 

range of POSS concentrations were synthesized by Lei Zheng [137] at the University of 

Massachusetts, Amherst. The synthesis is shown in figure 6-21. 

The thermal decomposition process of PE/POSS hybrid copolymer with 56 wt% of POSS is 

shown in figure 6-22. It can be seen that the introduction of POSS can greatly delay the major 

decomposition step of polyethylene by about 40°C and produce about 4% char. The copolymer 

starts to lose weight around 300°C, which is similar to the POSS monomer. The maximum mass

loss rate of the copolymer is the same as polyethylene, but it shifts to a higher temperature. 

6-20
FIGURE 6-21. COPOLYMERIZATION OF POLYETHYLENE WITH 

POSS-NORBORNENE [137] 

0 100 200 300 400 500 600 700

-100

-50

0

50

100

Temperature (oC)

Weight (%)

 PE

 PE/ 56wt% POSS

 Cp-POSS-norbonyl

0

20

40

60

80

100

120

Deriv. of Weight (%/min)

FIGURE 6-22. THE TGA AND DTG CURVES OF THE PE/POSS COPOLYMER 

The thermal decomposition products of the POSS monomer, PE/POSS copolymer and PE, are 

shown in table 6-9. Referring to the TGA results, the small weight loss of a copolymer between 

300°~450°C is due to the cleavage of the cyclopentyl side groups in the POSS monomer. At

high temperatures, the C-C backbone will randomly cleave into small aliphatic fragments, which

is similar to the random chain scission of PE. The high-molecular-weight silicon cage in the 

POSS monomer is not detected by pyrolosis GC/MS, which might be trapped in the GC column. 

TABLE 6-9. THERMAL DECOMPOSITION PRODUCTS OF 

PE/POSS COPOLYMERS 

Cp-POSS 1.3-cyclopentadiene, CO, CO2

PE/POSS

300°~450°C 1.3-cyclopentadiene, CO2

450°~930°C A series of alkanes, alkenes, and dienes 

PE A series of alkanes, alkenes, and dienes 

6-21
The flammability of PE/POSS copolymers with different amounts of POSS is shown in 

table 6-10. It can be seen that the introduction of the POSS monomer can systematically reduce 

flammability. Because the mass loss rate and char yield do not change significantly with the 

composition, the flammability reduction with increased POSS monomer is mainly due to the

release of more POSS volatiles with low flammability. It was also found that both the heat 

release capacity and total heat released of copolymers change linearly with the amounts of POSS 

monomer (figure 6-23). 

TABLE 6-10. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

PE/POSS COPOLYMERS 

POSS 

(wt %) 

H.R. 

Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

Char 

Yield 

(%) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

T99%

(°C) 

0 2007 41 0 8.83 474 363

19 1457 37 1.5 9.92 477 357

27 1330 35 1.8 11.68 486 336

37 1161 33 1.8 9.91 487 336

56 1034 32 3.9 8.83 487 328

100 314 19 4.6 7.86 455 293

0 20 40 60 80 100

0

500

1000

1500

2000

POSS (wt%)

Heat release capacity (J/g-K)

15

20

25

30

35

40

45

Total heat released (kJ/g)

FIGURE 6-23. FLAMMABILITY-COMPOSITION RELATIONSHIP OF 

PE/POSS COPOLYMERS 

6.3.4.2 Halogenated Comonomers—BPC-Epoxy Vinyl Ester Resins.

A group of cross-linked epoxy vinyl ester resins based on chlorobisphenol I and II (BPC I and II) 

were studied. The polymers were provided by Prof. Zbigniew Brzozowski at the Warsaw 

Institute of Technology. The syntheses are shown in figure 6-24. The composition of these 

polymers is summarized in table 6-11. 

6-22
(Styrene) 

FIGURE 6-24. SYNTHESIS OF CROSS-LINKED EPOXY VINYL ESTER RESINS 

BASED ON BPC I AND II 

TABLE 6-11. COMPOSITION OF BPC-BASED EPOXY VINYL 

ESTER RESINS (wt%) 

Polymers DGE BPC I DGE BPC II Ac MAc S S+PBBA 

A1 57% 19% 23%

A2 57% 19% 23%

A3 56% 20% 23%

A4 56% 20% 23%

B1 55% 21% 23%

B1 55% 21% 23%

B3 52% 24% 23%

B4 52% 24% 23%

Note: They all contain 1% benzyl peroxide (PBO) and 0.1% N, N-dimethylamine. 

The thermal decomposition processes of epoxy vinyl ester resins based on BPC I (A series) and 

BPC II (B series) are very similar. The TGA and high-temperature DSC curves of BPC II-based

epoxy vinyl ester resins (B series) are shown in figure 6-25. According to the TGA curves, they 

all show a two-step decomposition, in which the minor first step starts at approximately 

180°~220°C. The major second step starts at approximately 340°C. The introduction of

brominated monomer PBBA will reduce the thermal stability, but slightly increase the char yield. 

6-23
All the polymers can produce about 20% char up to 1000°C. They all show an obvious 

exothermic decomposition peak (about 140~180 J/g). For the polymers without PBBA, the 

exothermic peak is followed by an endothermic tail. For the polymers with PBBA, this tail 

totally disappeared. 

FIGURE 6-25. THE TGA AND DSC CURVES OF BPC II-BASED EPOXY VINYL ESTER 

RESINS (B SERIES) (a) TGA AND (b) DSC 

According to table 6-12, the flammability of these polymers is close to BPA-PC or Kevlar, 

which is significantly lower than BPA-based epoxy vinyl ester resin. The introduction of

brominated monomer PBBA cannot reduce the heat release capacity, but it can reduce the total 

heat released. The polymers containing methacrylic acid have slightly higher total heat of 

combustion than those with acrylic acid. 

6-24
TABLE 6-12. THERMAL DECOMPOSITION AND FLAMMABILITY OF BPC-BASED 

EPOXY VINYL ESTER RESINS 

Polymers 

H.R. 

Capacity 

(J/g-K) 

Total Heat

(kJ/g) 

Char 

Yield 

(%) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

T99% 

(°C) 

∆H 

(J/g) 

A1 197 18 28 1.31 345 187 178

A2 200 13 31 1.61 330 177 187

A3 229 20 28 1.44 344 168 136

A4 230 18 27 1.34 344 162 145

B1 373 17 32 4.60 387 164 194

B1 285 16 34 2.34 348 204 178

B3 325 21 24 3.37 384 190 176

B4 310 17 30 2.15 351 161 147

The thermal decomposition products are show in figure 6-26. It can be seen that the weight loss 

in the first step is due to the release of additives or solvents such as ethyl chloride, toluene, and

dibutyl phathalate. The major decomposition products of all the polymers are styrene and 

dibutyl phathalate. The polymers containing PBBA also release some brominated compounds. 

(a) 

Cl

O

O

O O

O

O

O O

OH

Br Br

Br

Br

Br

(b) 

CO2, 

CO 

FIGURE 6-26. PYROLYSIS GC/MS TRACES OF BPC I-BASED EPOXY VINYL ESTER 

RESIN A1 (a) 170°~330°C AND (b) 170°~930°C 

6-25
6.4 COMPOSITION—COPOLYMERS AND BLENDS.

6.4.1 Poly(Methyl Methacrylate)/Polystyrene Random Copolymers. 

A series of PMMA/PS random copolymers with 30, 40, 50, 60, and 70 mol% of PS was studied. 

They were obtained from Prof. Thomas Russell’s group at the University of Massachusetts, 

Amherst. All the polymers were synthesized by Craig Hawker at the IBM Almaden Research

Center through radical polymerization [138]. The number average molecular weight of these 

copolymers is 125 ~ 178 k and PDI is 1.4 ~1.8. Figure 6-27 shows the thermal decomposition

processes of these polymers. It was found that the thermal stability, decomposition rate, and the 

temperature at maximum mass loss rate all change systematically with the composition. With 

the increased amount of PS, the thermal stability increases, the decomposition rate increases, and

the decomposition peak is shifted to higher temperatures. 

0 100 200 300 400 500 600

0

10

20

30

40

50

60

Temperature (oC)

Deriv. of Weight (%/min)

 70% S

 60% S

 50% S

 40% S

 30% S

-100

-50

0

50

100

Weight (%/

min)

FIGURE 6-27. THE TGA CURVES OF PMMA/PS COPOLYMERS BY 

RADICAL POLYMERIZATION 

Table 6-13 summarizes the flammability and thermal decomposition properties of these 

copolymers. Corresponding to the systematic change in thermal decomposition, the heat release 

capacity and total heat released also change systematically. With the increased amount of PS, 

the flammability of the copolymers increases. According to figure 6-28, the total heat of 

combustion changes linearly with the composition. However, the heat release capacity does not 

show a significant increase until the copolymer contains more than 50 mol% PS. 

6.4.2 Poly(Methyl Methacrylate)/Polystyrene Blends.

A series of PMMA/PS blends with 0, 20, 40, 60, 80, and 100 mol% of PS were prepared by 

mixing PMMA and PS (both from Aldrich) in Tetrahydrofuran (THF), then solution casting into 

films. Figure 6-29 shows the thermal decomposition processes of these blends. Similar to the

copolymers, the thermal stability, decomposition rate, and the temperature at maximum mass 

loss rate all change systematically with the composition. With the increased amount of PS, the 

thermal decomposition processes are shifted to PS. 

6-26
TABLE 6-13. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

PMMA/PS COPOLYMERS 

PS 

(mol%) 

H.R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

T 95%

(°C) 

30 580 27 2.9 383 306

40 640 28 3.4 393 325

50 640 30 3.6 400 352

60 810 32 4.2 403 363

70 1000 33 4.9 406 369

0 20 40 60 80 100

0

500

1000

1500

2000

PS (mol%)

Heat release capacity (J/g-K)

20

25

30

35

40

Total heat released (kJ/g)

FIGURE 6-28. FLAMMABILITY-COMPOSITION RELATIONSHIP OF 

PMMA/PS RANDOM COPOLYMERS 

0 100 200 300 400 500 600

0

20

40

60

80

Temperature (oC)

Deriv. of Weight (%/min)

 PMMA

 20% PS

 40% PS

 60% PS

 80% PS

 PS

-100

-50

0

50

100

Weight (

%/)

FIGURE 6-29. THERMAL DECOMPOSITION PROCESSES OF 

PMMA/PS BLENDS 

6-27
Similarly to the random copolymers, the flammability increases systematically with the amount

of PS (table 6-14). The total heat of combustion changes linearly with the composition of 

blends, but the heat release capacity will not increase dramatically until the amount of PS is 

above 50 mol% (figure 6-30). 

TABLE 6-14. FLAMMABILITY AND THERMAL DECOMPOSITION OF 

PMMA/PS BLENDS 

PS 

(mol %) 

H.R. Capacity 

(J/g-K) 

Total 

Heat 

(kJ/g) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

T95% 

(°C) 

0 340 24 1.6 389 180

20 250 27 2.0 411 169

40 380 29 2.6 415 194

60 570 32 3.3 418 259

80 760 34 4.1 420 246

100 1200 37 5.2 421 356

0 20 40 60 80 100

0

500

1000

1500

2000

PS (mol%)

Heat release capacity (J/g-K)

15

20

25

30

35

40

45

Total heat released (kJ/g)

FIGURE 6-30. FLAMMABILITY-COMPOSITION RELATIONSHIP OF 

PMMA/PS BLENDS 

6.5 MOLECULAR WEIGHT.

PMMA, PS, and PEO were chosen to study the effects of the molecular weight on polymer 

flammability because they decompose by different mechanisms. 

6.5.1 Poly(Methyl Methacrylate).

All the PMMAs were obtained from Polymer Laboratories. They were synthesized by anionic 

polymerization using high-vacuum techniques. The polymerization was initiated with 2,2-

6-28
diphenyl hexyl lithium using a coordinating ligand salt and was terminated with alcohol by 

hydrogen abstraction. The peak molecular weights (Mp) of the samples measured by gel 

permeation chromatography were 30, 49, 64, 75, 88, and 480 kg/mole with a narrow molecular

weight distribution of 1.04 ~1.09. 

As shown in figure 6-31, the thermal decomposition processes of PMMAs with different 

molecular weights are very different. PMMAs with lower molecular weights such as 30 and 

49 k clearly show a two-step decomposition, but PMMAs with high molecular weights 

decompose in a single step and have relatively higher thermal stability. Correspondingly, the 

maximum mass loss rate occurs at high temperatures for the PMMAs with high molecular 

weight. 

100 200 300 400 500 600

0

20

40

60

80

100 30k

 49k

 64k

 75k

 88k

 480k

Weight (%)

Temperature (oC)

(a) 

0 100 200 300 400 500 600

3.0

3.6

3.2

3.0

2.8

6.5

480k

88k

75k

64k

49k

30k

Deriv. of Weight (x103/s)

Temperature (oC)

(b) 

FIGURE 6-31. THE TGA AND DTG CURVES OF PMMAs WITH DIFFERENT 

MOLECULAR WEIGHTS (a) TGA AND (b) DTG 

6-29
Corresponding to the DTG curves, the PCFC heat release rate curves of PMMAs shown in

figure 6-32 change from double peaks into a single peak. According to table 6-15, although the 

total heat of combustion of all the PMMAs is the same, their heat release capacity is mainly 

determined by the mass loss rates. Therefore, PMMAs with different molecular weight have 

different flammability. 

0 50 100 150 200 250

630

350

350

530

560

390

480k

88k

75k

64k

30k

49k

Heat release rate (J/g-K)

Time (s)

FIGURE 6-32. THE PCFC CURVES OF PMMAs WITH DIFFERENT 

MOLECULAR WEIGHTS 

TABLE 6-15. FLAMMABILITY AND THERMAL DECOMPOSITION OF PMMAs 

Mp

(kg/mole) 

H.R. Capacity 

(J/g-K) 

Total Heat

(kJ/g) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

T95% 

(°C) 

30 630 (d1) 25 6.5 275 261

49 350 (d2) 25 2.8 289 268

64 350 (d2) 24 3.0 380 298

75 530 (s) 24 3.2 376 325

88 560 (s) 24 3.6 379 321

480 390 (s) 25 3.0 370 308

*d: double peaks; 1 or 2: first or second peak; s: single peak

6.5.2 Polystyrene.

All the polystyrenes were also obtained from Polymer Laboratories. They were synthesized by 

anionic polymerization using inert gas blanket or high-vacuum techniques. The polymerization 

was initiated with n-butyl lithium and terminated with alcohol by hydrogen abstraction. The 

molecular weights (Mp’s) of the samples were 30, 50, 66, 96, 127, 220, 460, 553, 760, 

1030, 1130, 2880 kg/mole. The molecular weight distribution was polydispersity index 

(PDI) = 1.03~1.07. 

6-30
According to figure 6-33, the thermal decomposition processes of these polystyrenes with

different molecular weights are almost the same. As to the flammability (table 6-16), the heat

release capacity slowly increases with the molecular weight, but the change is not as evident as

in PMMA. 

350 400 450

-100

-50

0

50

100

Temperature (oC)

Weight (

%)

 30k

 96k

 127k

 220k

 460k

 2880k

0

20

40

60

80

Deriv. of Weight (%/min)

FIGURE 6-33. THERMAL DECOMPOSITION OF PS WITH DIFFERENT 

MOLECULAR WEIGHTS 

TABLE 6-16. FLAMMABILITY AND THERMAL DECOMPOSITION OF PS 

Mp

(kg/mole) 

H.R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

T95%

(°C) 

30 930 39 5.1 418 394

50 960 38 5.2 417 391

66 890 39 4.9 413 390

96 930 40 5.3 416 393

127 1000 40 5.5 418 395

220 1100 38 5.4 420 396

460 1100 39 5.6 418 396

553 1100 38 5.7 419 397

760 1100 38 5.5 420 398

1030 1100 40 5.6 418 391

1130 1200 39 5.7 419 398

2880 1300 40 5.8 420 398

6-31
6.5.3 Poly(Ethylene Oxide).

PEO samples were from Aldrich, which were inhibited with butylated hydroxy toluene. The 

molecular weights based on inherent viscosity were 8, 100, 300, 600, and 4000 kg/mole. 

According to figure 6-34, their decomposition processes are not changed with the molecular 

weight at all, nor is their flammability (table 6-17). 

300 400 500

-100

-50

0

50

100

Temperature (oC)

Weight (%)

0

10

20

30

40

50

 8k

 100k

 300k

 600k

 4000k

Deriv. of Weight (%/min)

FIGURE 6-34. THERMAL DECOMPOSITION OF PEO WITH DIFFERENT 

MOLECULAR WEIGHT 

TABLE 6-17. FLAMMABILITY AND THERMAL DECOMPOSITION OF PEOs 

Mp

(kg/Mole) 

H.R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

T95%

(°C) 

8 600 23 4.4 402 372

100 600 23 4.5 397 368

300 530 24 4.4 399 368

600 580 23 4.4 400 371

4000 680 24 4.3 398 366

6.5.4 Mechanisms of the Effects of the Molecular Weight.

Kashiwagi found that a number of properties affect the thermal and oxidative decomposition of 

thermoplastics, such as molecular weight, prior thermal damage, weak linkage, and primary 

radicals [132, 58, 139, 140]. Kashiwagi also found that there are two or three decomposition

stages in PMMA polymerized by free-radical initiation [140]. Generally, the first stage might be 

initiated by scission around the defects in the polymer chain such as head-to-head linkages. The 

next stage was proposed to be chain-end initiation due to the double bond-terminated polymer

chain. The last one is initiation by random chain scission. Kashiwagi believed because

anionically polymerized PMMA did not have many unsaturated double bonds at the ends, it

decomposed by random scission. 

6-32
However, according to the present results, anionically polymerized PMMAs with low molecular 

weights show a two-stage decomposition, which corresponds to the initiation of both end-chain 

and random-chain scission. It is believed that at low temperatures, the thermal decomposition

starts mainly from the chain end by stripping the monomers. At high temperatures, the polymer 

will randomly break along the chain and release monomers by unzipping (figure 6-35). For the 

PMMAs with high molecular weights, the number of chain ends is very limited. Therefore, the 

thermal decomposition is mainly initiated by the random chain scissions. As a result, PMMAs

with high molecular weights decompose in a single step. 

(1) First stage—End-chain initiation (low temperatures) 

C

CH3

COOCH3

CH2 C

CH3

COOCH3

H2C CH2 CH

CH3

COOCH3

C

CH3

COOCH3

CH2 C

CH3

COOCH2

CH2 CH

CH3

COOCH3

H2C

C

CH3

COOCH3

CH2 C

CH2

COOCH3

H2C CH3 CH

CH3

COOCH3

+

+

(2) Second stage—Random-chain initiation (high temperatures) 

C

CH3

COOCH3

CH2 C

CH3

COOCH2

CH2 C

CH3

COOCH3

C

CH3

COOCH3

CH2 C

CH2

COOCH3

CH3 C

CH3

COOCH3

H2C H2C +

FIGURE 6-35. THERMAL DECOMPOSITION OF PMMAs WITH LOW

MOLECULAR WEIGHT 

To summarize the experimental results, the effects of the molecular weight on polymer

flammability are greatly determined by their thermal decomposition mechanisms. For the

polymers that decompose by an unzipping mechanism such as PMMA and poly(α-methyl 

styrene), the molecular weight will have a big effect on thermal decomposition and flammability 

due to different chain-scission initiations. For the polymers that decompose by random chain 

scission, such as PEO, poly(ethylene), and most polycondensation polymers, the molecular 

weight does not have a dramatic effect on the flammability. For the polymers that decompose by 

a combination of unzipping and random scission mechanisms, such as polystyrene, molecular 

weight will have some effect on the flammability. 

6.6 FREE-RADICAL SCAVENGER—TEMPO.

Earlier it was found that the action of halogen flame-retardant systems could be enhanced 

substantially by the addition of peroxide in polystyrenics and polyolefins [7]. It has also been 

proposed that the free-radical inhibitor might retard the condensed-phase pyrolysis or surface 

oxidation of the burning process. In this study, blends of PS or PMMA with TEMPO and 

PS/PMMA random copolymers initiated by TEMPO were used to investigate how the freeradical scavenger TEMPO affects the flammability of polymers. 

6-33
6.6.1 Polystyrene or PMMA/TEMPO Blends.

PS/TEMPO blends with 2 wt% or 6 wt% of TEMPO were studied. PS and TEMPO were

obtained from Aldrich. According to figure 6-36, TEMPO is released around 150°C, which is 

well below the thermal decomposition temperature of PS. Therefore, it does not effect the 

decomposition rate and flammability of the blends (table 6-18). 

0 100 200 300 400 500 600

0

20

40

60

80

Temperature (oC)

Deriv. of Weight (%/min)

 PS

 2% TEMPO

 6% TEMPO

-100

-50

0

50

100

Weight (

%)

FIGURE 6-36. THE TGA AND DTG CURVES OF PS/TEMPO BLENDS 

TABLE 6-18. FLAMMABILITY OF PS/TEMPO BLENDS 

TEMPO 

(wt %) 

H.R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

0 1200 37

2 1100 37

6 1100 36

In PMMA/TEMPO blends, TEMPO can delay the second step of decomposition to higher 

temperatures (figure 6-37). However, it also increases the maximum mass loss rate. As a result, 

the heat release capacity is slightly increased (table 6-19). 

6.6.2 The PMMA/PS Random Copolymers Initiated by TEMPO.

A series of PMMA/PS random copolymers initiated by TEMPO were studied. All the polymers 

were obtained from Prof. Thomas Russell at the University of Massachusetts, Amhurst and were 

synthesized by Craig Hawker at the IBM Almaden Research Center [138]. The number average 

molecular weights of these polymers were around 10 k. The structure of the copolymer is shown 

in figure 6-38. 

6-34
0 100 200 300 400 500 600

0

10

20

30

40

Temperature (oC)

Deriv. of Weight (%/min)

 PMMA

 2% TEMPO

 6% TEMPO

-100

-50

0

50

100

Weight (

%)

FIGURE 6-37. TGA AND DTG CURVES OF PMMA/TEMPO BLENDS 

TABLE 6-19. FLAMMABILITY OF PMMA/TEMPO BLENDS 

TEMPO 

(wt %) 

H.R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

0 335 24

2 359 23

6 372 23

FIGURE 6-38. TEMPO-INITIATED PMMA/PS COPOLYMERS 

The TGA and DTG curves are shown in figure 6-39. It can be seen that with the increased 

amount of PS, the thermal stability of copolymers increases, but the peak of mass loss rate

becomes sharper and is shifted to the direction of PS, indicating the thermal decomposition 

becomes faster and is dominated by PS. 

According to table 6-20, both heat release capacity and total heat of combustion change 

systematically with the composition, that is, the flammability increases with more PS. However, 

neither of them changes linearly with the composition (figure 6-40). 

6-35
0 100 200 300 400 500 600

0

10

20

30

40

50

60

Temperature (oC)

Deriv. of Weight (

%/min)

 PS

 90% PS

 80% PS

 70% PS

 50% PS

-100

-50

0

50

100

Weight (

%)

FIGURE 6-39. THE TGA AND DTG CURVES OF TEMPO-INITIATED 

PMMA/PS COPOLYMERS 

TABLE 6-20. FLAMMABILITY AND THERMAL DECOMPOSITION OF PMMA/PS 

COPOLYMERS INITIATED BY TEMPO 

PS 

(mol %) 

H.R. Capacity 

(J/g-K) 

Total Heat 

(kJ/g) 

Max. Mass 

Loss Rate 

(x103

/s) 

Tmax

(°C) 

T95%

(°C) 

50 270 29 2.0 409 297

70 400 33 2.9 410 324

80 510 34 3.3 413 330

90 800 35 3.6 416 345

100 930 35 4.3 422 371

40 60 80 100

0

500

1000

1500

2000

PS (mol%)

Heat release capacity (J/g-K)

20

25

30

35

40

Total heat released (kJ/g)

FIGURE 6-40. FLAMMABILITY-COMPOSITION RELATIONSHIP OF PMMA/PS 

COPOLYMERS INITIATED BY TEMPO 

6-36
If these TEMPO-initiated PMMA/PS copolymers are compared with standard PMMA/PS 

random copolymers (figure 6-27), it can be seen that the thermal decomposition of the TEMPOinitiated copolymers spans a broader temperature range, and the mass loss rate is relatively 

lower. As a result, the flammability is lower. Some volatiles with TEMPO units are detected in 

the gas phase (figure 6-41). It is speculated that TEMPO can reduce the decomposition rate by 

recombining with the free radicals produced during decomposition, then releasing them through 

an equilibrium reaction (figure 6-42). 

S (a) 

MMA

MMA-S S-S

S-MMA-S

S-S-S 

MMA-S

S-S

S-MMA-S

S-S-S 

HO N

CH3CH2O N

MMA O N

(b) 

S 

MMA

FIGURE 6-41. PYROLYSIS GC/MS TRACES OF PMMA/PS COPOLYMERS (a) RANDOM 

COPOLYMER AND (b) TEMPO INITIATED 

HO CH2 CH CH2 CH CH2 C

CH3

COOCH3

CH2 C O N

COOCH3

CH3

HO CH2 CH CH2 CH CH2 C

CH3

COOCH3

CH2 C

COOCH3

CH3

(Rn )

+ O N

Rn + O N Rn O N

FIGURE 6-42. EFFECTS OF TEMPO ON POLYMER DECOMPOSITION 

6-37
6.7 DISCUSSION.

There are many factors that can affect polymer flammability. However, the most important one 

is the chemical structure of the polymers. Introducing aromatic or heteroaromatic rings and 

heteroatoms into a polymer main chain can efficiently reduce polymer flammability. The bulky 

side groups in polymethacrylates can be easily cleaved off and released as fuels. However, they 

can also expand the decomposition temperature range by multiple decomposition stages. As a 

result, the mass loss rates are reduced. The CN substituent is a very efficient flame-retardant unit 

to be incorporated into a polymer structure to increase char formation and reduce heat released.

The silicon-based or halogen-based comonomers that have low heats of combustion themselves 

can be used as reactive flame-retardant additives to adjust polymer flammability systematically. 

The silicon-based inorganic network structure can greatly promote the char formation. It was

also found that the effects of molecular weight on polymer flammability are dependent on the

thermal decomposition mechanisms of polymers. The introduction of TEMPO can slightly delay

the thermal decomposition of polymers if TEMPO does not volatilize before the decomposition

of polymers. For the copolymers and blends of PMMA/PS, the total heat of combustion 

generally changes linearly with composition, but the heat release capacity shows some

synergetic, i.e., adding a small amount of low flammable component (PMMA) can dramatically 

reduce the flammability. 

6-38
7. MOLECULAR MODELING OF THERMAL CYCLIZATION OF POLY(HYDROXYAMIDE).

7.1 INTRODUCTION. 

It is very difficult to predict everything that will happen in a fire. However, theoretical modeling 

provides an important tool to investigate and understand the fire properties of various materials 

and the reactions involved in the thermal decomposition and combustion process. 

There are two kinds of modeling. One is an empirical mathematical model based on mass and 

energy conservation to estimate the macroscopic fire behavior. For example, Lyon has 

developed a mechanistic mass loss model for char-forming polymers, from which the 

nonisothermal mass loss during constant heating rate can be effectively predicted [141]. The 

other is molecular modeling based on quantum and statistical mechanics to simulate the chemical 

structure and reactions numerically. Molecular modeling is a complementary method that can be

used as an adjunct to the experimental measurements and macroscopic modeling to provide new 

insights into the polymer flammability and fire resistance [142]. Therefore, it can help design 

new fire-retardant additives and fire-resistant materials on a molecular level. 

Dr. Marc Nyden of the NIST has successfully used the molecular modeling technique to identify 

factors that affect the condensed-phase thermal decomposition chemistry of polymers [143 and

144]. A novel computer program called MD-REACT has been developed. It is based on 

molecular dynamics and can account for the chemical reactions in the thermal degradation 

process of polymers. This code has been improved and extended [145]. 

Previous experimental results show that the thermal decomposition and flammability of PHA, its 

methoxy, phosphinate, and phosphate derivatives are quite different from each other though they 

have the same backbone structure (section 3). In order to have a better understanding of the 

thermal decomposition mechanism of these polymers, electronic structure methods Gaussian 98 

[77] were used to study the thermal decomposition process of PHA. The computations were 

carried out on systems in the gas phase. Considering the trade-off between computational cost 

and accuracy of result, the B3LYP [74 and 75] method with a 6-31G(d,P) [76] basis set was 

selected for the whole calculation. The thermal cyclization of PHA to PBO had been studied 

preliminarily by Rotem [146]. However, the model compounds Rotem used were very small in 

size and the method chosen was low-level Hartree-Fock (HF). In this research, to more precisely 

represent the structure of PHA and get high-quality quantitative prediction, a bigger model 

compound, a high-level density-functional theory (B3LYP) (the least expensive ab initio method, 

which includes the effects of electron correlation that are neglected in the HF method), and a 

6-31G(d,p) basis set were used. This part of the work was in collaboration with Stanislav 

Stoliarov [147]. 

7.2 PREVIOUS EXPERIMENTAL RESULTS. 

It was found that PHA, its methoxy, phosphinate, and phosphate derivatives decompose very 

differently in the first step (figure 7-1). However, they all show a new decomposition step

around 600°C, which is believed due to the decomposition of some similar structure that might 

contain some PBO rings. 

7-1
0 200 400 600 800 1000

0

20

40

60

80

100

Temperature (

o

C)

Weight (%)

0

5

10

15

20

25

30

35

DTG

TGA

11(-OPO(Ph)2)

1(-OH)

7

1

11 7(-OMe)

Deriv. of Weight (

%/min)

FIGURE 7-1. THERMAL DECOMPOSITION PROCESSES OF PHA 

AND ITS DERIVATIVES 

According to pyrolysis GC/MS, FTIR, and elemental analysis, PHA will cyclize into PBO by

releasing water during the first decomposition step (figure 7-2). However, if the hydroxyl groups 

are totally replaced by methoxy, phosphinate, or phosphate groups, these PHA derivatives cannot 

achieve the same cyclization as PHA without main-chain scission or cleavage of side groups. To 

understand how this small structural difference affects the cyclization reaction, the detailed 

cyclization pathway of PHA needs to be clarified. 

C PHAs

O

C

O

R2 R2

R1

RO

NH

OR

NH

PBOs

O

N N

O

R2 R2

R1

ROH

Cyclization ?

+

(H2O, CH3OH, phosphinate or phosphates)

R = H, CH3, PO(OPh)2, POPh2, PO(OMe)2, PO(OC2H5)2, PO(OPhCl2)2

 R1 = - or C(CF3)2

 R2 = H or Br

FIGURE 7-2. POSSIBLE THERMAL CYCLIZATION MECHANISM OF PHA 

AND ITS DERIVATIVES 

7-2
7.3 RESULTS. 

To know where the thermal decomposition is initiated, the weakest linkage along the polymer

chain needs to be identified. The bond dissociation energies of PHA and its methoxy and 

phosphate derivatives are shown in figure 7-3. It can be seen that the weakest bond in these 

PHAs is the bond between oxygen and hydrogen (PHA) or methyl (methoxy PHA) or phosphate 

groups (phosphate PHA). Especially, O-Me and O-P bonds in methoxy or phosphate PHAs are

much weaker than the O-H bond in PHA, which suggests that methyl and phosphate groups are 

more easily cleaved off during decomposition. The amide linkage in the polymer main chain is

the second weakest bond, which can cause the breakdown of polymer backbones as shown in 

methoxy PHA. 

NH

H

N

H

C

O

C

O

HO O

H

464

464

456

301

443

389

318

397

PHA-1 

N

H

C

O

C

O

HN

O

MeO

Me

209

401

Methoxy PHA 

N

H

C

O

C

O

HN

O

(MeO)2OPO

P O

MeO OMe

264

393

Phosphate PHA 

FIGURE 7-3. BOND DISSOCIATION ENERGIES OF PHA, ITS METHOXY AND 

PHOSPHATE DERIVATIVES (UNIT IN kJ/mol) 

The model compound selected is the smallest structure unit in PHA, which is involved in 

cyclization. The optimized structure of this model compound is shown in figure 7-4. It has two 

stable structures (PHA-1 and PHA-2) whose energy difference is only about 26 kJ/mol. The

transition between PHA-1 and PHA-2 can be easily achieved by rotation around the N-C bond in 

the amide linkage. The activation energy for this transition is only 63 kJ/mol in the model 

compound. 

7-3
63

26

PHA1

TS1

O

N O

O

H

N C TS1

O

H

N C

PHA2

H

O

H O

N C

H O

FIGURE 7-4. MOLECULAR STRUCTURES OF THE MODEL COMPOUND 

The thermal cyclization of PHA into PBO was proposed to proceed by the overall steps of ketoenol rearrangement followed by water release to form the PBO structure (figure 7-5). The

enthalpy changes in these two steps are 49 kJ/mol and -42 kJ/mol, respectively. The key step is 

the formation of the enol intermediate. 

 

OH

N

H

C

O

OH

N C

OH O

(1) (2) N

-H2O

FIGURE 7-5. PROPOSED CYCLIZATION MECHANISM OF PHA 

There are several pathways for the keto-enol transition. One is through a direct hydrogen shift, 

as shown in figure 7-6. The starting structure is PHA-2 with H and O atoms on the same side of 

the N-C bond. Then through a four-member ring transition state, the H atom is shifted to the 

carbonyl group and the C=N bond is formed. However, the energy barrier of this pathway is 154 

kJ/mol, which is too high compared with the activation energy (40 kJ/mol) observed in the TGA 

data. 

154

49

ENL1

TS2

PHA2

O

O N

O

H

N

H

C

O

O

H

O

N C

OH

H

FIGURE 7-6. KETO-ENOL REARRANGEMENT BY A DIRECT HYDROGEN SHIFT 

7-4
The second pathway for this keto-enol rearrangement is to form a six-member ring transition 

state, as shown in figure 7-7. At first, the amide linkage in the main chain and the hydroxy 

groups, which might come from the other PHA molecules or water, forms a six-member ring 

structure through intermolecular hydrogen bonding. Then by a concerted pericyclic reaction, the 

enol-intermediate ENL1 is formed. In this pathway, the energy barrier from the ordered complex 

to the six-member ring transition state is only 57 kJ/mol, which corresponds to the activation 

energy calculated by the TGA data. It can also be seen that the formation of hydrogen bonds is a 

very important step to form the enol intermediate. Methoxy and phosphate PHAs do not have 

hydroxyl side groups; therefore, they cannot form the hydrogen bonds that can lead to the 

formation of a six-member ring transition state. As a result, when they are heated up, they will 

not have the same cyclization reactions as PHA with hydroxyl groups but rather will cleave off 

the methyl or phosphate groups or have some main-chain scissions. 

C2H3OH1

57 89

TS3

+

C2H3OH2

O

PHA O

+

O

N

O

48 39

INT1

INT2

O

H

N

H

C

O

OH

+

N C

H O O

H

N C

OH

+

OH

H

O H

O

N C

H O H

H

O

O

N

H O H

H

O

O

C

C2H3OH1

57 89

TS3

+

C2H3OH2

O

PHA O

+

O

N

O

48 39

INT1

INT2

C2H3OH1

57 89

TS3

+

C2H3OH2

O

PHA O

+

O

N

O

48 39

INT1

INT2

O

H

N

H

C

O

OH

+

N C

H O O

H

N C

OH

+

OH

H

O H

O

N C

H O H

H

O

O

N

H O H

H

O

O

C

ENL1

FIGURE 7-7. KETO-ENOL REARRANGEMENT BY A SIX-MEMBER RING 

TRANSITION STATE

After enol-intermediate ENL1 is formed, it can be transformed into another enol structure 

(ENL2), which has a more favorable configuration for the final cyclization reaction. The ENL2

can be further transformed into ENL4, which might also be a structure leading to cyclization. 

All these transitions can be done by several rotations and bending motions. The activation 

energies of these transitions are about 50 kJ/mol (figure 7-8), which can be easily achieved at 

low temperatures. 

Starting with two different enol structures, ENL2 or ENL4, there are two mechanisms for

cyclization. For the ENL2, the aromatic C-OH bond and O-H bond in the enol structure will 

break first, then a water molecule is formed in transition state TS7. With the release of water, 

the rest of the structure collapsed into a ring. Therefore, the water released during cyclization is

formed by the phenolic hydroxyl side group and the hydrogen in the enol structure (figure 7-9). 

However, the activation energy of this reaction is about 267 kJ/mol. It is too high to be achieved 

at approximately 250°C. 

7-5
ENL1

23

TS4

49

O O

N ENL2

ENL4

ENL2 267

O O

N

TS7

H2O INT3

+

PBO

28 15

O

N

O

H

H

O

N

C + H2O

N

O

H

O

H

C

N

O

O H H

ENL2

43

29 14

TS5 ENL3

N 34

O O

TS6

FIGURE 7-8. ENOL-STRUCTURE TRANSFORMATIONS BY ROTATION AND BENDING 

FIGURE 7-9. CYCLIZATION INTO PBO THROUGH ENL2 INTERMEDIATE 

Another possible mechanism is through the ENL4 intermediate, as shown in figure 7-10. In this 

mechanism, the C-OH bond in an enol structure and O-H bond in a phenol group will break to 

form a water molecule and a biradical structure. After the water molecule is moved further away

from the biradical structure, the benzoxazole ring will form. In addition, it seems that the water

is not formed immediately after the bond breakage and needs a four-member ring transition state. 

The activation energy of this key reaction is only 126 kJ/mol, which can be easily achieved at 

250°C. Therefore, it is believed that the cyclization proceeds by this mechanism through the 

ENL4 intermediate. 

7-6
126

N

O

O

TS8

INT4

122

INT3

TS9

127

42

O

H

H

O

N

+ H2O

O H O

H

N C

O

H

N C

O O H H H

N C

O

N

O

C

ENL4

FIGURE 7-10. CYCLIZATION INTO PBO THROUGH ENL4 INTERMEDIATE 

7.4 DISCUSSION. 

The formation of the enol intermediate is the determining step in the thermal cyclization reaction

of PHA. The hydroxyl side groups in PHA play a very important role in forming a six-member 

ring transition state that can lead to the formation of enol structure later. Because methoxy and

phosphate PHAs cannot form this transition state through hydrogen bonds, they cannot cyclize in 

the same way as PHA. The water released during cyclization comes from the hydroxyl group in

the enol structure and the hydrogen in the phenol groups. 

7-7/7-8
8. CONCLUSIONS AND RECOMMENDATIONS.

8.1 CONCLUSIONS. 

Fire is a potential hazard for human life, especially in an enclosed and inescapable area, such as

high-rise buildings, submarines, ships, and aircraft cabins. Lightweight, high-performance

polymeric materials offer many advantages in these applications, but their inherent flammability 

greatly increases the fire risk. By exploring the intrinsic relationships between polymer 

structure, composition, and their fire behavior and understanding the thermal decomposition and 

fire-resistant mechanisms of polymers, the goal of this research is to help identify and design 

new fire-safe polymeric materials. 

8.1.1 Characterization of Thermal Decomposition and Flammability of Polymers.

Three significant milligram-scale experimental techniques, including pyrolysis GC/MS,

simultaneous thermal analysis (STA) and pyrolysis-combustion flow calorimeter (PCFC), have

been combined to fully characterize the thermal decomposition and flammability of different 

polymers and polymer composites. Each method stresses one specific aspect of the burning 

process of materials; therefore, they are complementary to each other. So far, the PCFC is the 

only accepted milligram-scale flammability test in the field of fire testing. It overcomes the

deficiencies of existing bench-scale heat release tests, which require relatively large amount of 

samples. In the PCFC test, heat release capacity obtained by the oxygen consumption principle 

is found to be a real material property. As a result, beyond rank ordering and simple product 

comparison, PCFC can provide significant additional insights for new product development. The 

combination of these three small-scale tests is efficient for screening newly synthesized fire-safe 

materials. However, the fire behavior of materials is a very complicated issue. It is associated

with not only many chemical reactions but also a series of physical processes. Therefore, the 

combination of PCFC method with some other large-scale flammability tests is especially

important for a comprehensive evaluation. 

The general thermal decomposition and flammability of different polymers ranging from highly 

flammable to highly fire resistant were studied. Generally, several important parameters can 

determine the ease of polymer combustion, including thermal stability, mass loss rate, the nature 

and properties of the decomposition products, and the char yield. The thermal stability of most

polymers ranges from 200°C poly(methyl methacrylate (PMMA) to 600°C polybenzthiazole

(PBZT), which greatly depends on the chemical structures of the polymers. Most aliphatic

polymers with hydrocarbon backbones, especially the ones with bulky side groups, are less 

stable than wholly aromatic polymers. Most homopolymers decompose in a single step, but 

some polymers such as PMMA and poly(vinyl chloride) decompose by multiple steps. The heat

of decomposition is another important parameter that is usually neglected due to the difficulty in 

measurements, especially for the aromatic high-charring polymers. Most polymers show an 

endothermic peak of 100 to 900 J/g. Very few polymers, such as charring halogenated polymers 

and polymers that can cyclize during decomposition, show exothermic peaks. 

By analyzing the decomposition products at different pyrolysis conditions, the thermal 

decomposition mechanisms can be identified. Some addition polymers with 1,1-substitution 

(PMMA) and some polyaldehydes poly(oxymethlene) (POM) usually decompose by an

8-1
unzipping mechanism. Most addition polymers and condensation polymers decompose by 

random scission mechanism.

Flammability was found to be the integrated effect of the thermal decomposition process and the 

properties of decomposition products. Generally, nonburning heteroatoms such as halogens, O, 

N, S and P, aromatic rings, heteroaromatic rings, and any units that can lead to the formation of 

cross-linking or fused-aromatic rings, are the fundamental structural units for the fire-resistant

polymers. All these structures can enhance char formation, reduce mass loss rate, reduce the 

amount of burning materials available, and produce volatiles with relatively low flammability. 

In addition, the quantum computation results show that there is no simple correlation between 

bond dissociation energy and activation energy calculated by thermogravimetric analysis (TGA) 

data. The relatively low thermal stability of aliphatic polymers measured by TGA sometimes is 

not because they have weaker bonds than aromatic polymers, but due to the easy release of lowmolecular-weight volatiles. 

On the other hand, the total heat of combustion and heat release capacity of polymers can also be 

estimated either by combining the results from pyrolysis GC/MS and STA or the chemical 

structures and TGA. The calculated values agree well with the results directly measured from

PCFC. 

8.1.2 Inherently Fire-Resistant Polymers.

The most efficient way to prevent polymer combustion is to design inherently fire-resistant 

polymers that have high thermal stability, resistance to the spread of flame, and low burning rate, 

even under high heat flux. 

8.1.2.1 Poly(hydroxyamide) and Its Derivatives.

Poly(hydroxyamide) (PHA) and some of its derivatives are potential candidates as solventprocessable, fire-resistant polymers. PHA and its halogen derivatives have extremely low 

flammability. They can totally cyclize into a poly(benzoxazole) (PBO) structure when heated to

250°C. Methoxy PHA is more thermally stable, but it exhibits higher flammability due to the 

main-chain scission at approximately 360°~400°C. Phosphinate or phosphate PHAs (PHA-10 

and -11) are very flammable due to the extensive cleavage of fuel-forming phosphinate and 

phosphate groups. However, the flammability of copolymers formed by the combination of 

different side groups is greatly reduced. 

Roughly, the thermal decomposition process of all the PHAs can be divided into two stages. In

the first stage (below 500°C), small molecules such as water, methanol, phosphinates, or 

phosphates, as well as their ester fragments, are released to form some quasi-PBO structures. In 

the second stage (above 500°C), the random scission of the polymer backbone with some

benzoxazole rings will occur. Most PHAs show an endothermic peak at low temperatures, but 

due to different mechanisms such as cyclization (PHA), melting (methoxy PHA), and 

decomposition (phosphate PHAs). Halogenated PHA-3 and -5 show a distinct exothermic 

decomposition peak at high temperatures due to the formation of HBr and some cross-linking 

8-2
reactions. However, PHA-1 shows a mixed endo- and exothermic behavior during hightemperature decomposition. Infrared spectroscopy, elemental analysis, and pyrolysis GC/MS all 

prove that the first decomposition stage of PHA-1 corresponds to cyclization to PBO. It was also 

found that the major decomposition products of most PHAs (except for phosphiante or phosphate 

PHAs) are CO, CO2, H2O, HCN, and a small amount of aromatic compounds. 

The low-flammable volatiles, low mass loss rates and high char yields are the major reasons for 

the low flammability of most PHAs. In addition, the endothermic cyclization of PHA and 

release of water might also increase the energy needed to sustain the whole combustion process.

Differently from the complete cyclization of PHA and halogenated PHA, methoxy-, 

phosphinate- or phosphate-substituted PHAs can only partially cyclize into PBO structures. 

8.1.2.2 Aromatic Polyarylates, Copolymers, and Blends.

Aromatic polyarylates make up another group of polymers with enhanced fire resistance. The 

three polyarylates based on bisphenol A (BPA), 1,1-dichloro-2,2-bis(4-hydroxy-phenyl)ethylene

(BPC II), and 4, 4’-dihydroxy-3-ethoxy-benzylidenoacetophenone (Chalcon II) are very

thermally stable up to at approximately 370°C. However, the introduction of bulky side groups 

or halogens in Chalcon II or BPC II can greatly reduce their thermal stability. It was found that

BPC II-polyarylate is an extremely fire-resistant thermoplastic with a char yield of more than

50% and dramatically low heat release rate and total heat released. Chalcon II-polyarylate is an

ultraviolet (UV)/visible-sensitive polymer. It also had a relatively low heat release rate and high 

char yield. However, the photo-cross-linking formed after UV/visible exposure had no effect on 

its flammability. 

The low flammability of Chalcon II-polyarylate was mainly due to its high char yield and low 

mass loss rate. However, the halogenated volatiles released by BPC II-polyarylate also 

contribute to its exceptional fire resistance. It is believed that the C=C bonds in both polymers 

can facilitate the char formation. The BPC-II unit is an especially valuable source for generating 

of char and HCl. 

Copolymerization or blending of two polymers with different thermal decomposition behavior

can efficiently adjust the flammability of the polymers. The total heat of combustion of 

polyarylate copolymers or blends was found to change linearly with the composition, but the 

change of peak heat release rate and char yield also greatly depends on the chemical structure of 

the components. Some synergetic effect was observed in some copolymers or blends, such as 

the blends of BPA-/BPC II-polyarylates or polysulfone (PSF)/BPC II-polyarylate. The results 

indicate that by adding only a very small amount of a low-flammable component such as BPC-II 

polyarylate, the heat release rate can be dramatically reduced. It was also found that at high 

content of BPC II-arylate units (>67 mol%), the flammability of the copolymers remains low and 

independent of the structure of the other component. Therefore, the BPC II unit is really an 

efficient flame-retardant agent for copolymers and blends. 

In all, the ideal fire-resistant polymers have the following characteristics: high decomposition 

temperature, low amount and release rate of volatile fuels, low heat of combustion of volatiles, 

high char yield, endothermic phase transition or decomposition, and release of chemical flameretardant molecules (halogen, water, etc.). 

8-3
8.1.3 Effects of Flame-Retardant Additives and Correlations Among Different Flammability 

Tests.

Flame retardants are widely used in the industry to reduce polymer flammability. Recently, due 

to some environmental concerns, searching for nonhalogenated flame retardants has become a 

major interest. In addition, evaluation of the efficiency of different flame retardants and how 

these flame retardants act in a fire still remain complex topics. 

It was found that inert fillers can reduce the flammability, mainly by its nonburning property

(mass-dilution effect) and promoting char formation. However, the addition of inert fillers can 

also change the physical properties of the materials such as thermal conductivity, density, and 

heat capacity that will affect the ignition and burning characteristics of the exposed surface. 

Therefore, the flame-retardant effect of the inert fillers in the Ohio State University (OSU) and 

cone calorimeter tests sometimes was not seen as dramatically as in PCFC tests. 

Halogenated flame retardants with or without antimony compound can reduce the flammability

by the inefficient combustion in the gas phase. The only disadvantages were that the thermal

stability of the materials was decreased and considerable corrosive smoke was generated. 

However, the flame-retardant effects of the halogenated additives were not significant in the

PCFC test. 

Polymer-clay nanocomposites are a new group of flame-retardant materials. However, the clay 

can only slow the heat release rate without changing the total heat released. The mechanism is 

purely based on the condensed-phase inhibition. 

The phosphorus-based additive is another group of promising flame retardants. They can form

an excellent foamy char barrier and, at the same time, reduce the gas-phase combustion 

efficiency. 

Depending on the composition, shape, form, and application of materials, different test methods

are required to ensure valid and accurate results. However, the results from one method 

generally cannot be directly related to the other due to different operating principles and 

experimental conditions. It was found that only for pure polymers, a relatively good correlation 

among PCFC, OSU, and cone calorimeter tests can be achieved. Polymer composites that 

contain flame retardants or inert fillers showed different flammability results in different tests.

There are several possible reasons. First, PCFC is not a direct flame-combustion test. In this 

test, the materials are first pyrolyzed at a controlled heating rate, and then the pyrolysis gases 

produced are totally oxidized in a separate high-temperature furnace. Therefore, the heat 

generated during combustion cannot be reflected back to the burning surface and cannot affect

the further decomposition of the materials, which is different from the situation in a real fire.

Secondly, due to the complete oxidation in PCFC, the effects of the additives, such as

halogenated additives that mainly act in the gas phase, cannot be achieved. As a result, the 

flame-retardant effects of these additives will be underestimated. However, OSU and cone 

calorimeter tests are real flame-combustion tests, and an interactive combustion cycle can be 

formed during burning. Therefore, any changes in condensed phase, gas phase or heat feedback 

will all be coordinately reflected in the overall flammability results. 

8-4
Nonetheless, because the PCFC method is more sensitive to the chemical structures of the 

materials, it is still a good screening tool for the pure polymers without additives or inert fillers.

However, OSU and cone calorimeter tests are the better flammability tests for composite 

materials.

8.1.4 Structure, Composition, and Flammability Relationships.

There are many factors that can affect polymer flammability, such as the chemical and physical 

characteristics of the polymers and specific burning conditions. However, the most important 

factor is the chemical structure of the polymers. 

It was found that introducing aromatic or heteroaromatic rings and heteroatoms into the polymer 

main chain can efficiently reduce polymer flammability. The silicon- or halogen-based 

comonomers that have relatively low heat of combustion on their own can be used as reactive 

flame-retardant additives to adjust polymer flammability systematically. The silicon-based

inorganic network structure can greatly promote the char formation. 

Different side groups also play a very important role in polymer thermal stability, decomposition 

process, and flammability. For example, the bulky hydrocarbon side groups in 

polymethacrylates can be easily cleaved off and released as fuels at low temperatures. However, 

due to the multiple decomposition stages, the decomposition temperature range of these 

polymers is extended. As a result, the decomposition rate and heat release rate sometimes can be 

reduced. On the other hand, the CN substituent was found to be a very efficient flame-retardant

unit to be incorporated into a polymer structure to increase char formation and reduce 

flammability. Generally, the bulky flammable hydrocarbon side groups should be avoided in

order to get good flame resistance. 

It was also found that some other factors, such as molecular weight, free radicals, and 

composition, can affect polymer flammability. However, the effect of molecular weight is

dependent on the thermal decomposition mechanisms of polymers. For the polymers that

decompose by an unzipping mechanism, such as PMMA, the molecular weight does have a big 

effect on their thermal decomposition and flammability due to different chain-scission initiation

mechanisms. However, for the polymers that decompose by random chain-scission mechanism,

the molecular weight does not have a big effect on their thermal decomposition and 

flammability. The introduction of TEMPO can slightly delay the thermal decomposition of 

polymers if TEMPO can remain in solid phase without volatilization. For the copolymers and 

blends of PMMA/ polystyrene(PS), the total heat of combustion generally changes linearly with 

composition, but the heat release capacity changes sluggishly until the copolymers or blends 

contain more than 50% of PS. 

In all, the ideal fire-resistant polymers have the following characteristics: high decomposition 

temperature, low amount and release rate of volatile fuels, low heat of combustion of volatiles, 

high char yield, endothermic phase transition or decomposition, and release of flame-retardant

molecules such as water or halogenated molecules. 

8-5
8.1.5 Thermal Cyclization Mechanism of PHA.

Previous experimental results show that PHA can completely cyclize into PBO around 250°~ 

400°C, but its methoxy and phosphate derivatives exhibit different behaviors upon heating. To 

understand how the cyclization of PHA occurs, an ab initio B3LYP method and 6-31G (d,p) 

basis set were used to investigate the thermal cyclization pathway of PHA. It was found that the 

formation of the enol intermediate is the rate-determining step during cyclization. The hydroxyl 

side groups in PHA play a very important role in forming a six-member ring transition state that 

can lead to the formation of an enol structure. Because methoxy and phosphate PHAs cannot 

form this transition state through hydrogen bonds, they cannot cyclize in the same way as PHA. 

The water released during cyclization comes from the hydroxyl group in the enol structure and 

the hydrogen in the phenol groups. 

8.2 RECOMMENDATIONS.

How to reduce the fire risks in human life is a very old research topic. In this dissertation, a 

detailed study on the thermal decomposition and flammability of polymers was performed by 

using different methods. Some fundamental understanding of the thermal decomposition and 

fire-resistant mechanisms was also proposed. However, considering the complex issues involved 

in a fire, there are still many aspects to be explored in the future. 

Establishing the PCFC method was a big advance in measuring heat release rate appropriate for 

normal laboratory use. It provides quantitative information useful for polymer development. 

Therefore, it has potential uses for screening, quality control, and production monitoring.

However, despite the large amount of research done so far, more research on instrument

development and utilization should be done in the years to come. One important aspect that 

should be focused on is applying the PCFC method to composite materials. Currently, only for 

pure polymer systems without flame retardants or inert fillers, it correlates well with the other 

two bench-scale flammability tests—OSU and cone calorimeter tests. This application limitation 

is mainly due to the separation of pyrolysis and combustion processes and the nonflame but 

complete oxidation process. Therefore, the experimental conditions used in the PCFC method 

do not exactly reflect realistic fire conditions. To improve this method, the instrument needs to 

be further modified, such as introducing a real flame in a microfurnace where both pyrolysis and 

combustion can be performed simultaneously. In addition, several important aspects should also 

be addressed. For example, standard operational procedures need to be clarified to improve 

validity of the measurements and rank different products according to their performance. Microscale, bench-scale, and full-scale correlations should be investigated, especially for polymer

composites. Real-time analysis of gas species during combustion can be used to verify the effect 

of halogenated additives. For the purpose of valid rank ordering, a fire characteristic index that 

integrates several fire-performance parameters (such as the ratio of peak heat release rate divided 

by the time to ignition) should be identified to collectively address the flammability of materials. 

During the last 30 years, many inherently fire-resistant polymers with different structures have 

been developed, but only a few have been commercialized due to their high cost and difficulty in 

processing. Because many fire-resistant structures such as different heteroaromatic rings have 

been explored, designing some exotic expensive structures would not be realistic. The imminent 

project is how to reduce cost and balance different properties such as flammability, 

8-6
processability, and mechanical properties so that all the fire-resistant polymers that have been 

successfully developed in the laboratory can be used in real life. Copolymerization and blending 

of different polymers with different thermal decomposition and flammability could be an ideal 

solution for this problem. It was found that by introducing only a small amount of fire-resistant 

components, the heat release rate can be dramatically reduced. On the other hand, properly 

selecting the other component can tailor some other properties to meet special requirements. For

example, PHA was found to be a good fire-resistant polymer, but it is very expensive and can 

only be processed in solution. If some chain-distorting groups such as bisphenol A, sulphone, 

and iso-aramide units are incorporated, the copolymers formed might be able to be meltprocessed at a proper composition. In addition, introducing chlorobisphenol C units into 

different aromatic polymers and polymer blends would also be an efficient way to reduce both 

polymer flammability and the amount of halogens inside polymers. These systems would also

be useful to study whether there is one clear relationship between composition and flammability 

for all the copolymers and blends. In all, identifying the fire-resistant units and properly 

combining them with other units to get the desired properties should be the most efficient way to

design new fire-safe polymers. 

Current environmental pressures require the development of new environmental-friendly flame

retardants to replace the halogenated additives, which are the most efficient and used in the 

largest volume so far. Although some new phosphorus- or silicon-based additives have been 

developed as the substituents, they are not as efficient as the halogenated additives. Therefore, 

searching for both environment-friendly and efficient flame retardants is still a very promising 

research direction, especially in the industry. However, if only a single element is considered, 

the choices are pretty much limited. To achieve the maximum efficiency and reduce the amount

of addition, the combination of different additives need to be considered. Because different 

additives act in different mechanisms and have different effects on different polymer systems,

some fundamental understanding of the flame-retardant mechanisms of these additives need to 

be applied when designing new systems. For example, the combination of gas-phase and 

condensed-phase inhibitions of halogen-P systems should be very efficient. In addition, how to 

induce polymer cross-linking and char formation by special chemical reactions is another 

possible way to reduce polymer flammability. 

Although some factors that can affect polymer flammability have been preliminarily studied,

more research needs to be conducted to further confirm the final conclusions. For example, the

effect of TEMPO radical on the flammability of PS is not significant due to the volatilization of

TEMPO at low temperatures. To avoid this problem, larger stable radicals can be used. In 

addition, it has been proposed that the molecular weight of polymers, which decompose by an 

unzipping mechanism, will affect their thermal decomposition and flammability. However, only

PMMA was studied in this research. More polymers such as POM and poly(α-methyl styrene) 

with the same decomposition mechanism need to be studied to prove the validity of this

conclusion. Furthermore, the threshold molecular weight of PMMA also needs to be identified. 

It was also found that Nomex

 has exceptional flame resistance compared to Kevlar, although

they have the same composition and are both aramides. The only difference between them is the 

para or iso linkage in amide groups. This observation raises one important question: Does the 

iso-type polymers always have lower flammability than para-type polymers? The investigation 

of some other type of polymers with para and iso structures will help clarify this question. In

8-7
addition, the structural integrity of materials during burning is another important issue. 

Therefore, studies of the residual mechanical properties of materials during decomposition are 

also of great significance. 

Using molecular modeling to further understand the thermal decomposition and fire-resistance 

mechanisms still needs to be strengthened. Several fundamental aspects need to be studied. For 

example, it was found that there is no simple correlation between the bond dissociation energy 

calculated by molecular modeling and the activation energy calculated by TGA data. This result 

seems contradictory to the belief that the activation energy should be directly related to the bond 

dissociation energy of the weakest bond because the thermal decomposition is supposed to be 

initiated by the breaking of the weakest bond. However, it also raises a question of what the

activation energy calculated by TGA represents. Generally, the TGA experiments measure the 

weight loss, which does not directly correspond to a single bond scission, especially for the 

polymers that decompose by random-chain scission mechanism. In these polymers, the TGA 

will not show a significant weight loss until small volatiles are formed by multiple bond

scissions. Therefore, the activation energy obtained is the consequence of the behavior of many 

bonds. In addition, for some high-charring aromatic polymers, the assumption of first-order 

decomposition for activation energy calculation does not hold. As a result, searching for a better 

model to calculate the activation energy should be done first. On the other hand, due to the 

limitation of computational methods, the experimental and calculation results need to be 

combined to get a valid explanation. Some calculations on high-temperature decomposition to 

predict various decomposition products would be valuable for future research. 

8-8
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9-1
18. “FAA Fire Test Handbook,” FAA report, DOT/FAA/CT-89/15, Washington, DC, 

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10-1/10-2
APPENDIX A—SUPPLEMENTARY DATA

TABLE A-1. GROSS HEAT OF COMPLETE COMBUSTION OF SMALL 

ORGANIC COMPOUNDS 

Formula Name

Referencea

(kJ/mol) 

Calculated (1)b

(kJ/mol) 

Calculated (2)c

(kJ/mol) 

Inorganic substances 

C Carbon (graphite) 393.5

H2 Hydrogen (g) 285.8

CO Carbon monoxide (g) 283 209.5 393.5 

H3N Ammonia (g) 382.8 380.2 428.7

H4N2 Hydrazine (g) 667.1 507.0 571.6

Hydrocarbons

CH4 Methane (g) 890.8 926.0 965.1

C2H2 Acetylene (g) 1301.1 1091.5 1072.8

C2H4 Ethylene (g) 1411.2 1345.0 1358.6

C2H6 Ethane (g) 1560.7 1598.4 1644.4

C3H6 Propylene (g) 2058 2017.4 2037.9

C3H6 Cyclopropane (g) 2091.3 2017.4 2037.9

C3H8 Propane (g) 2219.2 2270.9 2323.7

C4H6 1,3-Butadiene (g) 2541.5 2436.4 2431.4

C4H10 Butane (g) 2877.6 2943.4 3003

C5H12 Pentane (l) 3509 3615.9 3682.3

C6H6 Benzene (l) 3267.6 3274.4 3218.4

C6H12 Cyclohexane (l) 3919.6 4034.9 4075.8

C6H14 Hexane (l) 4163.2 4288.4 4361.6

C7H8 Toluene (l) 3910.3 3946.9 3897.7

C7H16 Heptane (l) 4817 4960.8 5040.9

C10H8 Naphthalene (s) 5156.3 5203.9 5078.2

Alcohols and ethers 

CH4O Methanol (l) 726.1 716.5 679.3

C2H6O Ethanol (l) 1366.8 1388.9 1358.6

C2H6O Dimethyl ether (g) 1460.4 1388.9 1358.6 

C2H6O2 Ethylene glycol (l) 1189.2 1179.4 1072.8 

C3H8O 1-Propanol (l) 2021.3 2061.4 2037.9

C3H8O3 Glycerol (l) 1655.4 1642.4 1466.3

C4H10O Diethyl ether (l) 2723.9 2733.9 2717.2 

C5H12O 1-Pentanol (l) 3330.9 3406.4 3396.5

C6H6O Phenol (s) 3053.5 3064.9 2932.6

A-1
TABLE A-1. GROSS HEAT OF COMPLETE COMBUSTION OF SMALL ORGANIC 

COMPOUNDS (Continued) 

Formula Name

Referencea

(kJ/mol) 

Calculated (1)b

(kJ/mol) 

Calculated (2)c

(kJ/mol) 

Carbonyl compounds 

CH2O Formaldehyde (g) 570.7 463.0 393.5

C2H2O Ketene (g) 1025.4 882.0 787

C2H4O Acetaldehyde (l) 1166.9 1135.5 1180.5

C3H6O Acetone (l) 1789.9 1807.9 1967.5

C3H6O Propanal (l) 1822.7 1807.9 1967.5

C4H8O 2-Butanone (l) 2444.1 2480.4 2754.5

Acids and esters 

CH2O2 Formic acid (l) 254.6 253.5 285.8 

C2H4O2 Acetic acid (l) 874.2 926.0 787 

C2H4O3 Methyl forrmate (l) 972.6 716.5 679.3 

C3H6O2 Methyl acetate (l) 1592.2 1598.4 1644.4

C4H8O2 Ethyl acetate (l) 2238.1 2270.9 2323.7 

C7H6O2 Benzoic acid (s) 3226.9 3274.4 3218.4 

Nitrogen compounds 

CHN Hydrogen cyanide (g) 671.5 545.7 536.4 

CH3NO2 Nitromethane (l) 709.2 380.2 428.7

CH5N Methylamine (g) 1085.6 1052.7 1108

C2H3N Acetonitrile (l) 1247.2 1218.2 1215.7

C2H5NO Acetamide (s) 1184.6 1262.2 1215.7

C3H9N Trimethylamine (g) 2443.1 2397.7 2466.6

C5H5N Pyridine (l) 2782.3 2728.7 2682

C6H7N Aniline (l) 3392.8 3401.2 3361.3

a

 Reference values from CRC Handbook of Physics and Chemistry 

b

 Calculated values based on oxygen consumption principle c

 Calculated values based on atom additivity principle 

A-2
TABLE A-2. NET HEAT OF COMPLETE COMBUSTION AND HEAT RELEASE CAPACITY OF POLYMERS 

A-3

Net Heat of Heat Release 

Mn Char a

Max. Mass 

Loss Rate a

Combustion

(kJ/g) 

Capacity

(J/g-K) 

Polymers Structure

Repeating Unit 

Composition (g/mol) (%) (%/s) PCFCb Calc. (1)c Calc. (2)d PCFCb Calc. (1)c Calc. (2)d

HDPE C H2 4 28 0 6.4 42e 44.89 45.38 1676 e 1724 1906

PP C H3 6 42 0 5.23 41 44.89 45.38 1584 1409 1424PS C H8 8 104 0 5.29 37 40.29 39.57 1199 1279 1256

POM CH O2 30 0 4.56 14 13.97 13.12 261 382 359

P(αmethyl

styrene) 

C H9 10 118 0 2.52 42 40.83 40.26 730 617 609

Nylon66 C12H22O N2 2 198 0 3.45 28 34.92 34.84 648 723 721

PEO C H2 O4 44 4 4.4 23 22.85 22.45 580 603 592

PPO C H8 O8 120 23 2.48 22 25.54 24.85 409 e 380 370

PET C10H O8 4 192 8 3.7 17 20.08 18.86 393 446 419

PC C16H14O3 254 17 3.8 19 24.74 23.82 382 564 543

CH

2

CH

CH2 CH2

CH2 CH

CH3

CH2

CH O

CH2

CHC

3

O

C (CH2)4

O

C NH (CH2)6 NH

CH2 CH2 O

O

O

C

O

C O CH2 CH2 O

O C

3

CH3

O C

O
TABLE A-2. NET HEAT OF COMPLETE COMBUSTION AND HEAT RELEASE CAPACITY OF POLYMERS 

(Continued) 

A-4

Net Heat of Heat Release 

Mn Char

Max. Mass 

Loss Rate 

Combustion

(kJ/g) 

Capacity

(J/g-K) 

Polymers Structure

Repeating 

Unit 

Composition (g/mol) (%) (%/s) PCFC Calc. (1) Calc. (2) PCFC Calc. (1) Calc. (2)

PMMA C H5 O8 2 100 0 2.06 23 25.14 24.51 376 311 303

BPApolyarylate C23H18O4 358 27 2.2 18 21.79 20.92 360 288 276

Kevlar C14H10O N2 2 238 32 1.96 15 18.62 17.88 292 219 210

PTFE C2F4 100 0 2.9 6 8.38 7.87 58 146 137

Poly(chloral) C HOCl 2 3 147.5 0 1.22 5 4.97 6.46 33 36 47

PEEK C19H12O3 288 46 2.2 13 16.09 15.37 163 212 203

BPApolysulfone C27H22O4S 442 31 3.3 17.0 19.95 19.23 336 395 381

Poly(ether 

sulfone) C18H12O4S 324 36 2.13 12 15.73 14.95 165 201 191

Poly(phenyl 

sulfone) C24H16O4S 400 45 1.71 13 14.98 14.32 156 154 147

PHA-OMe C22H18O N4 2 374 43 1.4 18 15.65 15.04 130 131 126

CH

CF

CH2 C

3

COOCH3

O C

CH3

CH3

O C

O O

C

O

C

O

C NH NH

CF2 2

CCCH

l3

O C

O R

N

95 5

O O

O

C

CHC

3

CH3

O S

OO

O

O

S

O

O S

OO

O

S O O

O

O

NH HN C

OMe MeO

O O

C
TABLE A-2. NET HEAT OF COMPLETE COMBUSTION AND HEAT RELEASE CAPACITY OF POLYMERS 

(Continued) 

A-5

Net Heat of Heat Release 

Mn Char

Max. Mass 

Loss Rate 

Combustion

(kJ/g) 

Capacity

(J/g-K) 

Polymers Structure

Repeating 

Unit 

Composition (g/mol) (%) (%/s) PCFC Calc. (1) Calc. (2) PCFC Calc. (1) Calc. (2)

Poly(amideimide) C28H17O N5 3 475 38 0.7 12 16.40 15.61 60 69 66

CyanoKevlar C15H O9 N2 3 263 58 0.77 9.1 10.80 10.32 55 50 48

PHA C20H14O N4 2 346 56 0.4 10 11.43 10.91 42 27 26

PI C16H O6 N4 2 290 50 0.5 8.5 11.18 10.73 29 34 32

BPC-PC C15H O8 Cl 3 2 307 53 1.3 5.7 9.94 9.41 29 78 73

PBZT C14H N6 2S2 266 58 0.38 5.0 10.30 9.89 24 23 23

Chalcon IIpolyarylate C25H18O6 414 41 0.9 10 15.82 15.05 110 85 81

Technora C34H24N O4 5 568 42 1.71 15.3 16.11 15.45 131 165 159

BPCpolyarylate C22H12O Cl 4 2 411 51 0.6 4.0 11.49 10.90 12 41 38

NH

C

N

O

C

O

O

C

O

C O NH

C C

O

NH

O

NH

CN

NH HN C

OH HO

O O

C

C

N

C C

N

C

OO

O

O

O C O

O

C

C

Cl Cl

NS

S

N

O

C2H5O

O

C O C

O

O

C

C NH O NH

O

C

O

NH

HN

O C

C Cl Cl

O C

O O

C
TABLE A-2. NET HEAT OF COMPLETE COMBUSTION AND HEAT RELEASE CAPACITY OF POLYMERS 

(Continued) 

A-6

Net Heat of Heat Release 

Mn Char

Max. Mass 

Loss Rate 

Combustion

(kJ/g) 

Capacity

(J/g-K) 

Polymers Structure

Repeating 

Unit 

Composition (g/mol) (%) (%/s) PCFC Calc. (1) Calc. (2) PCFC Calc. (1) Calc. (2)

XYDAR C27H16O6 436 40 2.55 11 16.14 15.41 215 247 236

PBT C12H1204 220 0 4.18 22 24.76 23.66 474 621 593

ULTEM C37H24O N6 2 592 49 12 14.44 13.79

Poly(ethyl

methacrylate) C H6 10O2 114 0 4.5 26 27.57 27.07 840 744 731

C2

O

O

C O O

O

C

O

C O

O

C C O (CH2)4 O

C OCH3CH3

O

C

N

O

C

O

C

N

O

C

O

CH2 C

H5

COOCH3

a TGA results. Heating at 10oC/min to 930oC in N2b PCFC results. Heating at 4.3oC/s to 930oC in N2c Calculated by oxygen consumption principle d Calculated by atom additivity principle e FAA data 
TABLE A-3. CORRELATION BETWEEN MOLAR FRACTION OF EFFECTIVE 

CHAR-FORMING ATOMS AND CHAR YIELDS OF POLYMERS 

Polymers Composition

Number of 

Effective Atoms

Effective Atoms 

(mol%) 

Char 

(%) 

PE CH2 0 0 0

PP C3H6 0 0 0

PS C8H8 0 0 0

Poly(a-methyl styrene) C9H10 0 0 0

Nylon 66 C12H22O2N2 0 0 0

PMMA C5H8O2 0 0 0

POM CH2O 0 0 0

PEO C2H4O 0 0 4

PTFE C2F4 0 0 0

Poly(chloral) C2HOCl3 0 0 0

PET C10H8O4 0 0 8

PBT C12H1204 0 0 0

PC C16H14O3 6 18 17

Poly(phenylene oxide) C8H8O 6 35 23 

BPA-polyarylate C23H18O4 12 27 27

BPA-polysulfone C27H22O4S 12 22 31 

Kevlar C14H10O2N2 12 43 32

BPC-PC C15H8O3Cl2 14 50 53

Cyano-Kevlar C15H9O2N3 16 55 58

Poly(ether sulfone) C18H12O4S 18 51 36 

Poly(methoxyamide) C22H18O4N2 18 39 43

PEEK C19H12O3 18 53 46

PI C16H6O4N2 18 64 50 

PBZT C14H6N2S2 18 75 58 

Chalcon II-polyarylate C25H18O6 20 41 41

BPC-polyarylate C22H12O4Cl2 20 50 51

XYDAR C27H16O6 24 49 40

Poly(phenyl sulfone) C24H16O4S 24 53 45

Poly(hydroxyamide) C20H14O4N2 24 60 56

Poly(amide-imide) C28H17O5N3 27 51 38 

Technora C34H24N4O5 30 45 42

ULTEM C37H24O6N2 30 43 49

A-7/A-8