Reference

;

NBS

PUBLICATIONS

NBSIR 84-3011

NAT'L INST. OF STAND & TECH

AlllDb 3 3 7 5

THERMAL AND MECHANICAL

PROPERTIES OF POLYURETHANE

FOAMS AND A SURVEY OF

INSULATING CONCRETES AT

CRYOGENIC TEMPERATURES

National Bureau of Standards

U.S. Department of Commerce

Boulder, Colorado 80303

April 1984

- : C

100

. U56

34-3011

1934

v

NBSIR 84-3011

THERMAL AND MECHANICAL

PROPERTIES OF POLYURETHANE

FOAMS AND A SURVEY OF

INSULATING CONCRETES AT

CRYOGENIC TEMPERATURES

L.L. Sparks*

J.M. Arvidson**

Chemical Engineering Science Division*

Center for Chemical Engineering*

Fracture and Deformation Division**

Center for Materials Science**

National Bureau of Standards

U.S. Department of Commerce

Boulder, Colorado 80303

April 1984

Prepared for Gas Research Institute

8600 West Bryn Mawr Avenue

Chicago, Illinois 60631

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIOWJU. BUKEJU) OF STAXDAJIDS

T.tiJEART QC/co

/j

no. SV-3

fJQ7 OQ u/

NATIONAL BUREAU Oh STANDARDS, Ernest Ambler. Director

THERMAL AND MECHANICAL PROPERTIES OF POLYURETHANE FOAMS

AND A SURVEY OF INSULATING CONCRETES AT CRYOGENIC TEMPERATURES

FINAL REPORT

(January 1979 - February 1984)

Prepared by

L. L. Sparks* and J. M. Arvidson**

*Chemical Engineering Science Division

**Fracture and Deformation Division

National Bureau of Standards

Boulder, Colorado 80303

For

GAS RESEARCH INSTITUTE

Grant No. 5081-353-0425

GRI Project Manager

Dr. Kiran Kothari

Environment and Safety Department

April 1P84

GRI DISCLAIMER

LEGAL NOTICE This report was prepared by National Bureau of Standards

as an account of work sponsored by the Gas Research Institute (GRI).

Neither GRI, members of GRI, nor any person acting on behalf of either

a. Makes any warranty or representation , express or implied, with

respect to the accuracy, completeness, or usefulness of the

information contained in this report, or that the use of any

apparatus, method, or process disclosed in this report may not

infringe privately owned rights; or

b. Assumes any liability with respect to the use of, or for damages

resulting *rom the use of, any information, apparatus, method, or

process disclosed in this report.

SO 777 1QI REPORT DOCUMENTATION

PAGE

1. REPORT NO. GRI-R4/00R6

3. Recipient's Accession No.

«. TUN and Subtitle Thermal and Mechanical Properties of Polyurethane

Foams and a Survey of Insulating Concretes at Cryogenic

Temperatures

5. Report Oat* April 1984

7. Author**) L. L. Sparks and .1, M. Arvidson

8. PerformI og Organization Rapt. No. NBSIR 84-3011

Performing Organization Nam* and Address Chemical Engineering Science Division

National Bureau of Standards

325 Broadway

Boulder, CO 80303

10. Profact/Ta*k/Work Unit No. 7733574 and 7730403

11. Cootract(C) or Grant(G) No. (o 5081-352-0425

(G)

12. Sponsoring Organization Name and Addras* Gas Research Institute

8600 West Bryn Mawr Avenue

Chicago, IL 60631

13. Typo of Report & Period Covered Final , Jan 1979-Feb 1984

14.

IS. Supplementary Not**

IS. Abatract (Limit: 200 words) . , Thermal and mechanical properties of expanded plastics, foams, are reported. The

system studied was rigid, closed cell, CCJI 3 F blown, polyether based polyurethane. The

primary temperature range of study was 100 to 300 K; however, several properties were determined to 4 K. The nominal densities of the foams tested were 32, 64, and 96 kg/nr.

Properties reported are thermal conductivity, thermal expansion, strength and moduli in

tension and in compression, proportional limit, yield strength, ultimate strength, and

shear strength. Physical properties were determined both parallel and perpendicular to

the orthogonal axes of the bulk supplies. The gas content of the specimens was determine!

using a gas chromatograph-mass spectrometer and with a gas displacement pycnometer. Empirical procedures for estimatinq the temperature dependent thermophysical properties were developed. These procedures are based on the experimental data and utilize the character

ization parameters for molar gas concentration, qas pressure, and cell morphology.

Regulations affecting vapor dispersion in the area around liquefied natural qas facilities make it attractive to construct dikes and impounding areas out of materials having low thermal conductivities. Several insulating concretes have the general properties

required for such applications. Screening tests were done to determine the thermal con- ductivity, modulus of rupture, and the compressive strength of several polyester based

materials with glass bead or perlite aggregate and of Portland cement based materials wit1 ' vermiculite or polystyrene aggregate. A bibliography resulting from an extensive literature survey of lightweight concretes is presented. Seven of the references which were particularly applicable are presented in annotated form.

17. Document Analysis a. Descriptors cell size; compressive strength; elongation; flexural strength; foam; glass head;

insulation; low temperature; mechanical properties; modulus of rupture; perlite;

polyester; oolymer concrete; polystyrene; portland cement; proportional limit; shear

strength; tensile strenqth; thermal conductivity; thermal expansion; vermiculite; yield

strength; Young's modulus.

b. Identifier* /Open-Ended Term*

c. COSATI Flald/Group

18. Availability Statement 18. Security Class (This Report) UNCLASSIFIED

Unlimited; NTIS, Springfield, VA 22161 20. Security Claes (This UNCLASSIFIED

21. No. o4 Page*

160

22. Price

(See ANSI—Z39.18) See Instructions on Reverse OPTIONAL FORM 272 (4-77) (Formerly NTIS-J5) Oep»rimen« o* Commerce
.
RESEARCH SUMMARY

Title Thermal and Mechanical Properties of Polyurethane Foams and a

Survey of Insulating Concretes at Low Temperatures

Contractor National Bureau of Standards

GRI Grant Number 5081-352-0425

Principal

Investigator

L. L. Sparks

Report

Period

January 1979 - February 1984

(Final Report)

Objective To determine the thermal and mechanical properties of polyurethane

foams and, whenever possible, to develop predictive techniques for

the low temperature properties. To survey existing data for and to

conduct screening tests on several insulating concretes in order to

allow selection of the most viable candidate materials for further

use and development. The temperature range of interest for both

foams and concretes is that encountered in the transfer and storage

of liquefied natural gas (LNG).

Technical

Perspective

Expanded plastics or foams are used extensively as thermal insulation materials in liquefied fuel facilities. The widespread use of

these materials can be attributed to low thermal conductivity, high

strength-to-weight ratio, low cost of production, and ease of installation. The properties of foam insulations, which are

vi i
essential to the design of facilities and production of foam, are

not adequately predictable at this time. The needed predictability

must be based on either theoretical or empirical representations

that include the dependence on temperature and the effects of

critical parameters such as cell size, gas content, and density.

Regulations concerning vapor dispersion in the event of a spill at

a LNG storage facility make it attractive to use an insulating

material in the construction of dikes and impounding areas. Several types of insulating concretes are candidates for such applications. Identification of one or more of these materials, along

with the development of an adequate data base for the selected

materials, is necessary for confident design.

Results The effort involving plastic foams has resulted in the following

experimental data for each of the three polyurethane foams studied:

thermal conductivity, thermal expansion, strength and moduli in

compression and in tension, proportional limit, yield strength, ultimate strength, and shear strength. Foam specimen densities were

nominally 32, 64, and 96 kg/m^ and the basic temperature range of

the study was 100-300 K. Empirical techniques were established to

predict thermal conductivity, thermal expansion, and compressive

and tensile strength and moduli. The empirical nature of these relationships and the small number of foam systems involved in their

development mean that appl icabi 1 i ty to polyurethane foams in general has not been established.

vi i i
studied depend, in varying degrees, on cell gas, morphology, and

chemical composition of the resin.

The effort directed to insulating concretes is a study of these

materials, as a class, for applications to dikes and impounding

areas at cryogenic temperatures . The literature survey resulted in

very limited data applicable to the projected use of these materials. An experimental screening program was conducted on three

polyester resins with glass-bead and perlite fillers and two

portl and-cement mixes with vermiculite and polystyrene fillers.

The screening consisted of determining the thermal conductivity at

several temperatures between 76 and 285 K (high vacuum environment)

and determining the modulus of rupture (MOR) and compressive

strength at 76 and 300 K.

ASTM standard methods C78 and C513 were used to determine MOR and

compressive strength respectively at both ambient and cryogenic

temperatures.

Project A large data base on thermophysical properties of foams at cryoImpl i cations

genic temperatures has been generated. Empirical relationships

were developed to predict thermal conductivity, thermal expansion,

and strength properties of the foams utilizing experimental data.

These parameters will be used in insulation design for cryogenic

fluid transfer pipes and storage tanks.

x
Technical

Approach

A survey of existing data for insulating concretes has been completed. The survey yielded approximately 300 pertinent references,

of which 30 contained data applicable to LNG facilities. Screening

tests, done to supplement data from the literature, have been completed. These tests resulted in comparative data for thermal conductivity, modulus of rupture and compressive strength for several

polyester-based materials with glass bead or perlite aggregate and

for portl and-cement-based materials with vermiculite or polystyrene

aggregate. Thermophysical properties and low water absorption required for dike insulation materials recommend polyrner-based materials over portl and-cement-based materials. Portland-cement-based

materials could also be produced which, with waterproofi ng and

proper grading of dike/basin surfaces, would be suitable.

The thermophysical properties of expanded plastics depend on

morphology, gas content, and chemical composition. A wide variety

of techniques have been used to determine these parameters. The

most fruitful methods are gas chromatography/mass spectrometry, optical analysis of polarized photomicrographs and pycnometry. These

analyses yield statistical information on cell size, cell shape and

orientation, and cellular gas content. In addition to specimen

characterization, the experimental study consisted of determining

thermal conductivity (ASTM C177 dry-nitrogen environment), AL/L in

an optical -1 ever dilatometer (helium-gas environment), and the

mechanical properties in a system utilizing a specially designed

capacitance extensometer (helium-gas environment). All properties

ix
From a literature survey and from limited experiments, six potential materials for dike insulation at LNG facilities have been

identified. Two of the recommended materials composed of polymer

binder with perlite or glass nodules as the aggregate are being extensively tested in a GRI-sponsored project at Brookhaven National

Laboratory.

GRI Project Manager

Kiran M. Kothari

Project Manager, LNG Safety

xi
Table of Contents

Page

GRI Disclaimer iii

Research Summary vii

List of Tables xiv

List of Figures xvi

Introduction , 1

Insulating Foams 2

Overall Project Objective (IF) . 2

Project Description (IF) 2

Project Rationale and Projected Benefits (IF) 5

Technical Discussion (IF) . ........ 6

Work Plan (IF) . . 6

Work Performed and Experimental Results (IF) 8

Discussion of Results and Modeling (IF) 70

Major Achievements (IF) 88

Major Technical Problems (IF) 89

Conclusions (IF) 89

References (IF) 91

Insulating Concretes .... 95

Overall Project Objective (IC) 95

Project Description (IC) ..... 95

Project Rationale and Projected Benefits (IC) 96

Technical Discussion (IC) 97

Work Plan (IC) 97

Work Performed and Results (IC) 97

Discussion of Results (IC) 102
Table of Contents ( continued )

Page

Major Achievements (IC) Ill

Major Technical Problems (IC) Ill

Conclusions (IC) Ill

Recommendations (IC) 112

References (IC) 114

Annotated Bibliographies (IC) 134

xi i i
List of Tables

Table

1 Maximum intercepted cell dimensions parallel to the

orthogonal principal axes of the XY S XZ, and YZ planes for

four specimens of PU32 and two specimens each of PU64 and

PU96. Locations of the specimens are indicated in figure 2 . . .

2 Ratios of averaged maximum intercepted cell dimensions

parallel to the orthogonal principal axes of the XY, XZ,

and YZ planes for four specimens of PU32 and two specimens

each of PU64 and PU96. Locations of the specimens are indicated in figure 2 .

3 Intercepted cell section area computed from cell wall intercept data for two specimens each of PU32, PU64, and PU96.

The method of computation follows that described by Schael

(1967). Locations of the specimens are indicated in figure 2 . .

4 Results of gas comparison pycnometer (GCP) character!’ zation

of PU32, PU64, and PU96. Comparable results from optical

evaluations of the same materials are also given

5 Cell gas composition of PU32, PU64, and PU96 (Barkley, 1983).

One standard deviation for the CCJI3F contents is +10% . . . .

6 Average thermal conductivity as a function of average temperature for a 32-kg/m^ polyurethane foam

7 Average thermal conductivity as a function of average temperature for 64- and 96-kg/m^ polyurethane foams

Polynomial coefficients representing the thermal expansion of

32-, 64-, and 96-kg/m^ polyurethane foams. Reference temperature is 293 K

Page

13

14

15

16

18

23

25

31

9 Thermal expansion and coefficient of thermal expansion for a 32-kg/m^ polyurethane foam ,

10 Thermal expansion and coefficient of thermal expansion for a 64-kg/m^ polyurethane foam

11 Thermal expansion and coefficient of thermal expansion for a 96-kg/m^ polyurethane foam

12 Summary of tensile test results for a 32-kg/m3 polyurethane

foam (average values)

13 Summary of compressive test results for a 32-kg/m^ polyurethane foam (average values)

14 Summary of shear strength test results for a 32-kg/m^ polyurethane foam (average values)

35

35

36

63

64

64

xiv
List of Tables

Table Page

15 Summary of tensile test results for a 64-kg/m^ polyurethane foam (average values) 65

16 Summary of compressive test results for a 64-kg/m^ polyurethane foam (average values) 66

17 Summary of shear strength test results for a 64-kg/m^ polyurethane foam (average values) 67

18 Summary of tensile test results for a 96-kg/m^ polyurethane

foam (average values) 68

19 Summary of compressive test results for a 96-kg/m^ polyurethane foam (average values) 69

20 Summary of shear strength test results for a 96-kg/m^ polyurethane foam (average values) 70

21 Computed values of thermal conductivity components based on initial vapor-pressure temperatures as determined from

thermal conductivity data 75

22 Pressure-induced strain parallel to the measurement direction

calculated as a function of internal and external pressures and

Young's moduli (longitudinal). External pressures were 89.3 kPa

for PU32 and PU96 and 84.0 kPa for PU64 78

23 Thermal contraction of the resins and the calculated transverse

thermal contractions of PU32, PU64, and PU96 as determined from

the pressure-induced stress and Young's moduli (transverse) ... 80

24 Parameters needed to estimate the thermophysical properties of

polyurethane foams as a function of temperature 90

25 Industrial sources of information and/or materials used in the

NBS/GRI survey of insulating concretes. This list is not com- prehensive in regard to companies involved with lightweight

concretes and no endorsement is implied 103

26 Density, thermal conductivity (k), compressive strength (CS),

and the ratio Q

= CS/k for the lightweight concretes tested

at NBS and for several materials reported in the literature.

The data are for 295 K 110

xv
Figure

List of Figures

Page

1 3

2

3

4

5

6

7

8

9

10

11

12

13

14

Tasks associated with the insulating foarn project

Bulk supplies of polyurethane foam and orientation of axes. Numbered rectangles indicate areas used for characterization . .

Configuration of the planes studied by optical methods . . . . .

Orientation of the elongated cell axes. These results are from optical examinations of the bulk supplies of these

materials

Schematic of the system used to obtain samples of cell

gas from fluorocarbon blown polyurethane foams

Schematic of the guarded-hot-plate thermal conductivity

apparatus ......

Schematic of guarded-hot-plate specimen configuration and

environmental chamber

Total apparent thermal conductivity of fluorocarbon blown

polyurethane foams of nominal densities 32. 64, and

96 kg/m3 ........ .

Schematic of dilatometer developed for inhomogeneous, anisotropic materials

Thermal expansion of a 32-kg/m3 polyurethane foam specimen.

Experimental data are represented by discrete points and the

solid line represents a three-term polynomial fit to these

data. The reference temperature is 281.997 K

Thermal expansion of a 64-kg/m3 polyurethane foam specimen.

Experimental data are represented by discrete points and the

solid line represents a three-term polynomial fit to these

data. The reference temperature is 295.180 K

Thermal expansion of a 96-kg/m3 polyurethane foam specimen.

Experimental data are represented by discrete points and the

solid line represents a three-term polynomial fit to these

data. The reference temperature is 292.227 K

Results of three-term polynomial fits to the thermal expansion

of 32-, 64- , and 96-kg/m3 polyurethane foam specimens. Refer- ence temperature is 293 K

Coefficient of thermal expansion rel ationships resulting from

temperature derivatives of three-term polynomial fits to

thermal expansion data of 32-, 64-, and 96-kg/m3 polyurethane

foam specimens

9

10

12

17

19

20

24

26

28

29

30

32

33

XV

1
List of Figures ( continued )

Figure Page

15 Extensometer systems which utilize the capacitance of concentric cylinders. Uniform and reduced section tensile specimen

geometries are also illustrated 34

16 Tensile Young's modulus versus temperature for a 32-kg/m^

polyurethane foam 38

17 Tensile test results: proportional limit, yield strength, and

ultimate strength versus temperature for a 32-kg/m^

polyurethane foam 39

18 Tensile strain versus temperature for a 32-kg/m3 polyurethane

foam 40

19 Compressive Young's modulus versus temperature for a 32-kg/m^

polyurethane foam 41

20 Compression test results: proportional limit, yield strength,

and maximum compressive strength versus temperature for a 32-kg/m3 polyurethane foam 42

21 Compressive strain versus temperature for a 32-kg/m^ polyurethane foam 43

22 Shear strength versus temperature for a 32-kg/m^ polyurethane foam 44

23 Tensile Young's modulus versus temperature for a 64-kg/m^

polyurethane foam 45

24 Tensile strength versus temperature for a 64-kg/m^ polyurethane foam 46

25 Tensile strain versus temperature for a 64-kg/m^ polyurethane

foam 47

26 Compressive Young's modulus versus temperature for a 64-kg/m^

polyurethane foam . . . 48

27 Compressive strength versus temperature for a 64-kg/m^ polyurethane foam 49

28 Compressive strain as a function of temperature for a 64-kg/m^

polyurethane foam 50

29 Shear strength versus temperature for a 64 -kg/m^ polyurethane

foam 51

30 Tensile Young's modulus versus temperature for a 96-kg/m^

polyurethane foam 52

xvi i
List of Figures ( continued )

Figure Page

31 Ultimate tensile strength versus temperature for a 96-kg/m3

polyurethane foam 53

32 Tensile strain versus temperature for a 96-kg/m3 polyurethane foam 54

33 Tensile stress versus strain for a 96-kg/m3 polyurethane

foam 55

34 Compressive Young's modulus versus temperature for a 96-kg/m3

polyurethane foam 56

35 Compressive strength versus temperature for a 96-kg/m3 polyurethane foam 57

36 Compressive proportional limit versus temperature for a 96-kg/m3

polyurethane foam 58

37 Compressive yield strength versus temperature for a 96-kg/m3

polyurethane foam 59

38 Compressive strain versus temperature for a 96-kg/m3 polyurethane foam 60

39 Compressive stress versus strain for a 96-kg/m3 polyurethane foam 61

40 Shear strength versus temperature for a 96-kg/m3 polyurethane foam 62

41 Thermal conductivity as a function of temperature for gases

commonly found in polyurethane foams (Touloukian, Li ley, and

Saxena, 1970) 72

42 Parameters affecting the measured thermal expansion of expanded

plastic foams 76

43 Longitudinal (experimental) and transverse (calculated) thermal

contraction of PU32, PU64, and PU96 81

44 Calculated thermal contraction of polyurethane as a function of

density with temperature as the parameter 82

45 Young's modulus of polyurethane foam in tension as a function of

density with temperature as the parameter. The modulus obtained

here must be modified by a function of (H/W) for a specific

material

xvii i

84
List of Figures ( conti nued )

Figure Page

46

Strength of polyurethane foams in tension as a function of

density with temperature as the parameter. Strength obtained

here must be modified by a function of (H/W) for a specific

material

47 Young's modulus of polyurethane foam in compression as a function of density with temperature as the parameter. The modulus

obtained here must be modified by a function of (H/W) for a specific material

48 Compressive strength of polyurethane foam as a function of

density with temperature as the parameter. The strength obtained here must be modified by a function of (H/W) for a particular material

49

Thermal conductivity as a function of temperature with

moisture content (Lentz and Monfore, 1955) and density (Adams,

1969) as parameters

50

Splitting strength as a function of temperature for an expanded

shale concrete with density of 1554 kg/m3 (Monfore and Lentz,

1962)

51

Compressive Young's modulus as a function of temperature for

an expanded shale concrete of density 1554 kg/m3 (Monfore

and Lentz, 1962)

52 Compressive strength as a function of temperature for expanded

shal e/portl and (Monfore and Lentz, 1962) and for several lightweight concretes at 295 K (McClune and Moorhouse, 1981) . . . .

53 Thermal conductivity of several insulating concretes as a function of temperature. The testing environment was insulating vacuum

54 Average compressive strength of several insulating concretes

as^a function of temperature (determined at NBS)

55 Average modulus of rupture of several insulating concretes as

a function of temperature (determined at NBS)

85

86

87

98

99

100

101

104

105

106

xix

Thermal and Mechanical Properties of Polyurethane Foams and a Survey of

Insulating Concretes at Cryogenic Temperatures

INTRODUCTION

Safe and economical storage and transport of cryogenic fuels such as liquefied natural gas (LNG) depend to a large extent on the materials used in the construction of storage tanks, transfer terminals, liquefiers, pipelines, and ships.

Thermal insulation constitutes a critical link in the materials for use in LNGand LPG (liquefied petroleum gas) -oriented energy efforts because of the cryogenic nature of the liquids. Two types of insulating material are being studied

--expanded plastics and lightweight concretes. Insulation systems utilizing expanded plastics (foams) are used in many LNG-oriented facilities. An insulating

concrete can satisfy requirements for dike and impounding areas of LNG storage

tanks.

The data bases and knowledge based on experience for both types of material

being considered are inadequate for reliable design. Most data for insulating

foams are based on essentially uncharacterized specimens. Consequently, it is

not generally possible to reliably relate existing data to a particular foam.

Inefficient overdesign and failures may occur because the material actually used

is different than the material used to determine the design properties. Insulating concretes have not been used extensively in applications where they must be

functional at cryogenic temperatures. There is not enough information available

to allow a particular type of lightweight material to be chosen with confidence.

Unanswered areas of concern are application difficulties, initial cost, maintenance costs, deterioration, and thermal and mechanical properties.

This project was designed to alleviate these difficulties. The portion of

the project devoted to foams will be discussed first and will be identified by

(IF) for insulating foams. Discussion of insulating concretes will follow and

will be designated by (IC).
INSULATING FOAMS

Overall Project Objective (IF)

There are four major objectives of the foam project:

(1) To improve the existing data base and the test procedures relating to expanded plastics at low temperatures.

(2) To develop test methods and characteri zation procedures for general application to foam insulations.

(3) To provide a basic understanding of the observed low-temperature behavior

and to develop procedures that can be used to predict low-temperature properties of insulating polyurethane foams.

(4) To serve as a center for insulation information for GRI and associated users

of cryogenic fuels.

Project Description (IF)

The work performed on insulating foams can be correlated with the major

tasks shown in figure 1.

(1) Assessment of Materials - A literature search was made. Companies and technical societies involved in the production and/or use of insulating foams were

contacted. The results of this phase of the project were reported by Sparks

(1979, 1980). Based on the information obtained, three densities of expanded

polyurethane foam were chosen as materials for detailed study. The densities

span the range normally used in insulating applications.

(2) Assessment of Methods - This effort was performed concurrent with task (1)

since the same literature survey and industrial contacts were involved. With the

exception of thermal conductivity, there are no existing standard test procedures

- 2 -
Development

of

Characterization

Figure

1.

Tasks

associated

with

the

insulating

foam

project.
for expanded plastics at low temperatures. This task, therefore, necessarily in

volved evaluation of apparatuses and procedures used at NBS and in industry.

Special apparatuses were ultimately required for adequate testing of thermal expansion and mechanical properties of these viscoelastic, anisotropic materials.

(3) Characterization - The development of predictive techniques for foam proper

ties requires knowledge of morphology, cell gas, and chemical composition of the

test specimens. Several methods of determining these parameters were evaluated

during the course of the project. The criteria used in determining the final

role of the various techniques was quality and usefulness of the output and

whether or not the procedure could be reasonably applied by producers and users

of polyurethane foams. The following procedures were evaluated: (a) Gas

chromatograph/mass spectrometer - used to determine the composition of the gases

present in the foam cells, (b) Scanning electron microscopy (SEM) - reflected

beams of electrons produce photographs with depth of field much superior to

optical photographs, (c) Photomicrography - an optical microscope designed specifically to observe grain structure in metals was used to study the cell structure of the 32-kg/m3 foam, (d) Polarized photomicrographs-polarized light enhances resolution of cell structure and was used to study the cell structure of

the 64- and 96-kg/m3 foams, (e) Thermogravimetric analysis (TGA) - used to determine mass loss as a function of temperature. The results were used to identify constituent material’s in the foams, (f) Differential scanning calorimetry

(DSC) - used to determine heat capacity as a function of temperature. Temperature dependent phase changes can be detected using this technique, (g) Gas comparison pycnometry - used to study foam morphology.

- 4 -
(4) Specimen Acquisition - Bulk supplies of 32- and 64-kg/m3 specimens were

obtained from the Products Research Committee (1980) through the Office of

Standard Reference Materials of NBS. The 96-kg/m3 material was purchased from

a commercial producer.

(5) Testing - Several basic properties were considered to be essential to the

use of insulating foams in the LNG industry. In addition to the characteri zation

tests, the following types of data were obtained for each of the three polyurethane specimens: thermal conductivity, thermal expansion, coefficient of thermal

expansion, tensile, shear, and compressive strengths. Young's modulus, proportional limit, yield strength at 0.2% offset, and elastic and plastic elongation.

The temperature range of study always included 100 to 300 K, and in several instances, data were obtained from considerably outside this range.

Project Rationale and Projected Benefits (IF)

Expanded polyurethanes are complicated composite materials. The values of

most thermophysical properties depend on the direction of heat flow or stress application relative to the direction of free foam expansion during polymeri zation.

Aging affects the properties both due to gas diffusion and to resin changes. The

net result is that current use of insulating foams in cryogenic applications involves costly overdesign and, in some instances, undesirable results. Much of

the existing low temperature data for foams is based on uncharacterized materials

and were determined with experimental methods unsuited for low temperature testing.

The rationale for the study of insulating foams was to alleviate the problems currently faced by designers of foam insulation systems. The three-fold

thrust to accomplish this was: (1) to generate reliable low temperature data for

- 5-
three polyurethane foams whose densities span the range of practical insulating

foams; (2) to utilize these data to develop predictive procedures for low temperature properties; and (3) to establish a direction for further low temperature

research on expanded plastics. Important complimentary research includes examination of test procedures and design of special equipment to study foam-like materials. Also, the possibility of developing a foam standard reference material

needed to be examined.

The benefits of items (1) and (2) above are clear and immediate. The data,

can be used as an engineering guide for initial design of polyurethane insulation

systems. The predictive procedures can be used to further refine expected behavior when used in conjunction with specific foam characteri sties. The highest

quality design data for a specific foam must be based on information about the

particular foam formulation and on an understanding of the effect of different

foam characteristics on the low temperature properties. In order for this to be

done in a practical way, standardized tests and materials must be readily

available. Ultimately, the economic and safe utilization of these insulating

materials in LNG applications depends on further research to bring expanded

plastics to the level of development of other materials used in LNG facilities.

TECHNICAL DISCUSSION (IF)

Work Plan (IF)

The work plan for the duration of the foam study followed the general steps

outlined in the Project Description section. The early stage of the work was devoted to selecting the most useful type of insulation for LNG applications and to

determine what, if any, standard procedures existed to allow reliable low temperature data to be generated. A significant literature search had been done and

industrial contacts were al ready established for an earlier project. Evaluation

- 6 -
of data and procedures indicated that most materials tested previously could not

be identified well enough to be of use in developing predictive procedures and

that the only standard procedure that could be readily applied at cryogenic temperatures was ASTM C177 for thermal conductivity. Two experimental systems

suited to testing viscoelastic anisotropic foams were near completion at NBS.

Characterization of the foams presented another obstacle. The literature and

fundamental parameters in thermophysical properties suggested that the morphology

of a foam and the statistical size, shape, and orientation of the cells was of

primary importance. Several papers dealing with measurement techniques and interpretation (Smith and Guttman, 1953; Harding, 1960; Schael , 1967 ; and Thompson,

1972) were evaluated and utilized, in part, to characterize the polyurethane

specimens.

A large number of procedures for determining various attributes of the materials were evaluated. The primary characterization effort centered on determining the cellular structure optically and determining the cellular gas content using a gas chromatograph backed by a mass spectrometer. An important consideration in both testing and characterization was that the procedures be such that

they could be adopted for general use. This is particularly important for characterization of foams: predictive procedures will be more useful if the parameters can be determined with reasonable effort.

After proving the experimental systems and acquiring and characterizing the

specimens, the following thermophysical properties were determined for each of

the three polyurethane foams: thermal conductivity, thermal expansion, tensile,

shear, and compressive strengths. Young's modulus, proportional limit, yield

strength at 0.2% offset, and elastic and plastic elongation. The results of the

testing program were to be assessed for the possibility of describing the

measured values with analytical models.

- 7-
Work Performed and Experimental Results (IF)

The nominal densities of the polyurethane foam specimens were 32, 64, and

96 kg/m3 (PU32, PU64, and PU96). PU32 and PU64 were obtained from the NBS

Office of Standard Reference Materials (OSRM), Washington, D.C. The OSRM distributed these and other expanded plastics for the Products Research Committee

(1980). These materials were commercially produced and distributed by OSRM as

General Materials. The third material, PU96, was purchased from a commercial

manufacturer, since OSRM did not stock a General Material in this density range.

The bulk supplies of these materials were in the forms shown in figure 2. The

coordinate axes assigned to the bulk materials are indicated in this figure. The

thermal expansion, thermal conductivity, and longitudinal mechanical property

measurements were made parallel to the z-axis. The transverse mechanical properties were measured parallel to the y-axis.

Densities - The densities of the bulk supplies were determined for four

specimens of each material. After conditioning at 23 °C and 50% relative

humidity, the densities were found to be 33.56 + 0.14, 62.52 + 0.11, and 99.03

+ 3.4 kg/m3

. The uncertainties represent estimates of one standard deviation.

The large uncertainty in the PU96 density results from a density variation in the

bulk supply.

Optical characterization - Optical characteri zation involved three general

procedures: (1) examination of the bulk supplies by means of a binocular microscope with an extension arm, (2) maximum-cel 1 -dimension analysis of polarized

photomicrographs of the principal orthogonal planes, XY, XZ, YZ in (fig. 3), and

(3) analysis of cell-wall intercepts at 30° rotations for the planes XY, XZ, and

YZ (fig. 3).

Bulk examination - This examination was intended to reveal the existence of

nonvertical flow lines, i.e., foam rise directions not parallel to the z-axis.

- 8

-
Figure 2. Bulk supplies of polyurethane foam and orientation of axes. Nuntered

rectangles indicate areas used for characteri zation.

- 9

-
Figure 3 Configuration of the planes studied by optical methods.

- 10 -
This type of examination of PU32 indicated that the elongated cell axes were not

vertical at any place in the bulk supply, and that the cells near the long edges

(approximately 0.3 m in from each long edge) were inclined about 35° in the XY

plane, 45° in the XZ plane, and 55° in the YZ plane (fig. 4). Cells in the

center portion had 0° inclination in the XY and YZ planes, but retained the 45°

inclination in the XZ plane. These qualitative assessments were confirmed in the

quantitative intercept analysis discussed below.

The bulk supply of PU64 consisted of three slabs. Nonvertical flow lines

were observed in each of the pieces but the angle of inclination was smaller than

that found in PU32. The cellular inclinations of two of the three slabs were

consistent and identical within the uncertainty of the measurements (fig. 4).

The inclinations found in the third slab were not uniform, i.e., the inclination

was significantly different for parallel planes. No additional tests were performed on this slab. The slab designated PU64-1 was used for mechanical property

tests and PU64-3 was used for thermal property tests.

Non-vertical alignment of the long cellular axes of PU96 was found only in

an 0.08 m thickness around the perimeter. A 0.2 m thickness around the perimeter

was marked as scrap, and no test specimens were taken from this material. The

cellular orientation for all planes of PU96 are shown in figure 4.

Maximum-cel 1 -dimension analysis - This procedure was used to determine the

ratios of maximum cellular dimensions parallel to the major axes. Microscope

slides were made by passing a blade through the foam at a given orientation.

This procedure was done with the cutting planes parallel to the principal planes:

XY, XZ, YZ. Photomicrographs were prepared with a minimum of two different sections per plane for each foam. It was found that a magnification of 50 was suitable and that the contrast achieved using incident, polarized light produced

clearly defined cell boundaries. Maximum cell dimensions parallel to the

- 11 -
12

Figure

4,

Orientation

of

the

elongated

cell

axes.

These

results

are

from

optical

examinations

of

the

bulk

supplies

of

these

materials.
principal axes were determined from the length calibrated photographs. Results

of these measurements are given in table 1. The lengths measured and presented

Table 1. Maximum intercepted cell dimensions parallel to the orthogonal principal axes of the XY, XZ, and YZ planes for four specimens of PU32 and

two specimens each of PU64 and PU96. Locations of the specimens are indicated in figure 2.

Specimen X Axis

(urn)

Y Axis

(urn)

Z Axi s

( um)

PU32-2 527 406 488

PU32-3 492 380 510

PU32-6C1 482 356 458

PU32-6C2 461 364 457

PU32-average 490 376 478

PU64-1 213 218 348

PU64-2 208 221 333

PU64-average 210 220 340

PU96-1 272 240 257

PU96-2 226 250 300

PU96-average 249 245 278

in this table represent the maximum intercepted dimension which is somewhat

smaller than the actual maximum cell dimension. Several authors (Hensler, 1968;

Exner, 1969; and Thompson, 1972) have proposed multiplicative factors needed to

arrive at actual maximum cell dimensions from maximum intercepted cell

dimensions.' These factors range from 1.5 to 1.68 with the differences being due

to assumptions about cell shape and packing factors. The ratios given in table 2

eliminate this source of uncertainty.

Intercept analysis - The procedure used to arrive at these data also utilizes photographs of foam cells and follows the acquisition scheme suggested by

Smith and Guttman, 1953. This approach assumes randomly oriented sections.

- 13 -
Table 2. Ratios of averaged maximum intercepted cell dimensions parallel to the

orthogonal principal axes of the XY, XZ, and YZ planes for four speci- mens of PU32 and two specimens each of PU64 and PU96. Locations of the

specimens are indicated in figure 2 .

Specimen z/x Z/Y X/Y

PU32-average 0.98 1.27 1.30

PU64-average 1.62 1.55 0.95

PU96-average 1.12 1.13 1.02

Randomness was approximated by seven planes, XY, XZ, YZ and planes P^ through

P 4 in figure 3, for each of two locations per material, i.e., 14 photographs

for each of the three polyurethane foams. Each photograph was evaluated by

superimposing a grid of parallel lines and counting the intersections of grid

lines and cell walls. Data were taken for grid rotations of 0, 30, 60, and 90

degrees. Statistical evaluation of these data, as suggested by Schael , 1967, results in the cross-sectional areas listed in table 3. The quality of these data

depend strongly on how nearly the sampling procedure produces a random cross section of the foam. If randomness is assumed, these data are independent of cell

shape.

Gas comparison pycnometry - Acquisition of cellular data by optical means is

tedious and its interpretation is time consuming. Gas comparison pycnometry

(GCP), as discussed by Harding (1960), Rice and Nunez (1962), and Schael (1967),

can theoretically be used to obtain similar data more rapidly. This technique

requires only commercially available equipment and, after adopting an appropriate

experimental procedure, could be done on a routine basis.

The principle of GCP operation is Boyle's law: the product of pressure and

volume of an ideal gas is constant at a given temperature. The quantity actually

determined is specimen volume as measured by gas displacement, i.e., volume of

foam as determined by GCP would be smaller than the physical dimensions of the

- 14 -
Table 3. Intercepted cell section area computed from cell wall intercept data

for two specimens each of PU32, PU64, and PU96. The method of computation follows that described by Schael (1967). Locations of the speci- mens are indicated in figure 2.

Specimen XY 9P1 ane

(cnr/cel 1

)

XZ9P1 ane (cnr/cell

)

YZ9 Plane

(cnr/cel 1

)

PU32-2 1.27 X 10- 3

1.21 X 10-3 1.25 X 10"3

PU32-3 1.02 X IQ'

3 1.32 X IQ'

3 1.11 X 10~ 3

PU32-average 1.15 X l(f

3 1.27 X 10" 3 1.18 X 10" 3

PU64-1 2.90 X 10-4

4.23 X 10' 4

4.59 X 10“4

PU64-2 2.59 X IQ'

4

4.19 X 10"4

4.83 X 10"4

PU64-average 2.75 X 10" 44.21 X 10'4

4.71 X 10"4

PU96-1 5.51 X 10"45.53 X 10‘4

4.69 X

1

rH O

PU96-2 4.74 X 10' 4

4.69 X 10‘ 45.88 X 10"4

PU96-average 5.13 X 10-4

5.11 X 10‘45.29 X 10‘4

specimen would indicate because of open cells. By sectioning a foam specimen in

a particular sequence and making multiple determinations of the resulting

specimen GCP volumes, information on open cell content, cell size, and axial dimensions can be calculated. Several GCP operating procedures were evaluated.

The procedure selected for use involved subjecting the test specimens to a pressure variation from 0.4 to 200 kPa of nitrogen gas. An individual GCP test required only minutes to complete so that diffusion of gas and concomitant changes

in internal pressure were assumed to be negligible. Results of the GCP analysis

and a comparison to optically obtained values are given in table 4.

The optical data are internally consistent, i.e., if elliptical cross sections are assumed, the axial dimensions can be used to compute the cellular cross

sectional area to within the uncertainty of the data. This is not true for the

GCP data for either the cellular volume of cross section. However, as will be

- 15 -
Table 4. Results of gas comparison pycnometer (GCP) characterization of PU32,

PU64, and PU96. Comparable results from optical evaluations of the

same materials are also given.

Parameter

PU32 PU64 PU96

GCP Optical GPC Optical GPC Optical

Average Cell Volume, 11.7 5.76 4.06 4.05

. n-5 3

10 cm

Fraction Open Cells, %

Plane XY 5.9 0.9 2.4

Plane XZ 6.3 3.4 5.0

Plane YZ 3.4 4.0 4.0

Cellular Cross-Section

-3 2

, 10

0

crn Plane XY 4.75 1.15 1.40 0.275 1.55 0.513

Plane XZ 5.06 1.27 2.25 0.421 2.67 0.511

Plane YZ 3.24 1.18 2.59 0.471 2.10 0.529

Axial Dimensions, ym

X Axis 247 490 123 210 153 249

Y Axi s 224 376 142 220 120 245

Z Axis 338 478 227 340 207 278

Axial Ratios

Z/X 1.37 0.98 1.85 1.62 1.35 1.12

Z/Y 1.51 1.27 1.60 1.55 1.72 1.13

X/Y 1.10 1.30 0.87 0.95 1.28 1.02

seen later, the essential quantities in the predictive procedures are the axial

ratios. These ratios. computed using GCP and optical data, are in reasonable

agreement.

Cell -gas analysis - An important component of thermal conductivity of

closed-cell foams is gas conduction. The composition of the gas in the cells was

determined in order to allow this component of the apparent conductivity to be

assessed. Gas samples were obtained using the system shown in figure 5. The

procedure was as follows: (1) A 3.5 cm^ specimen was placed in the crushing

device (fig. 5b) and sealed using an indium ring. (2) The crusher was attached

to the purge system (fig. 5a). (3) System pressure was reduced to 50 kPa absolute followed by a helium-gas backfill to 115 kPa. This step was repeated 20

- 16 -
To Purge and

Sampling Port

Specimen

Crusher

Figure 5. Schematic of the system used to obtain samples of cell gas from

fluorocarbon blown polyurethane foams.

- 17 -
times and resulted in an air content, external to the foam, of 1 ppm.

(4) Crusher and foam were cooled to liquid nitrogen temperature and the plunger

depressed. The brittle foam specimens were reduced to a compacted powder assuring that essentially all cells had been fractured. (5) A gas specimen was drawn

into a gas-tight syringe and inserted into the analysis system. Steps (1)

through (5) were repeated on four specimens from each of the three polyurethane

foams.

The analysis system consisted of a gas chromatograph column with a massspectrometer detector (Barkley, 1983). The averaged results of the analysis are

shown in table 5.

Table 5. Cell-gas composition of PU32, PU64, and PU96 (Barkley, 1983). One

standard deviation for the CCJI 3

F contents is + 10%.

Mole %

Specimen CCfcgF 0^ It,

PU32-1 93.6 2.2 4.2

PU32-2 93.6 2.2 4.2

PU32-3 94.7 2.0 3.4

PU32-4 90.6 4.0 5.4

PU32-average 93.1 2.6 4.3

PU64-1 92.8 2.8 4.4

PU64-2 91.8 3.3 4.9

PU64-3 83.0 5.4 11.6

PU64-4 93.6 2.2 4.2

PU64-average 90.3 3.4 6.3

PU96-1 87.0 2.0 10.5

PU96-2 95.2 1.0 4,5

PU96-3 94.2 2.4 3.0

PU96-4 96.2 0.4 2.9

PU96-average 93.2 1.5 5.2

Thermal conductivity - The apparatus used to make the thermal conductivity

(k) measurements is shown schematically in figures 6 and 7. The path of the

- 18 -
FLUID

IN

Temperature

Controlled Shield

Vacuum Insulated

Transfer Tube

Throttle Valves

Shroud

Shroud Cooling

Tubes

Top Cold Plate

Bottom Cold Plate

FLUID

’out**

Vacuum Insulated

Transfer Tube

Figure 6. Schematic of the guarded-hot-plate thermal conductivity apparatus.
ENVIRONMENTAL CHAMBER

LIQUID COOLED SHROUD

OUTER GUARD

TOP COLD PLATE

OFFSET INSULATION

TOP AUXILIARY HEATER PLATE

O

I-<

_iD

COz

SPECIMEN

z

o

I-<

—ID

CO

INNER

GUARD MAIN HEATER PLATE INNER

GUARD

HEATER

PLATE

(METERED SECTION) HEATER

PLATE

z

O

D

C/5 Z

SPECIMEN

z

o

D

co

BOTTOM AUXILIARY HEATER PLATE

OFFSET INSULATION

BOTTOM COLD PLATE

A

\\\Y\T\~\\ \ \\ \\ \\ \\ \\ \\ \\ XXX

BASE

Figure 7. Schematic of guarded-hot-plate specimen configuration and

environmental chamber

- 20-
cooling fluid is shown in figure 6 and the details of the specimen configuration

are shown in figure 7. This type of system is commonly known as a guarded-hotplate and is described in the American Society for Testing and Materials Standard

C177 (ASTM, C177). This method allows an absolute determination of k and is considered to be the most accurate method available for insulations. The particular

apparatus used to make the k measurements reported here is described by Smith,

Hust, and Van Poolen (1981); a very brief description is included below.

The basic operation of this type of apparatus involves supplying a measured

amount of power, Q, from the main heater plate to the two specimens (fig. 7) and

measuring the resulting steady-state temperature differences across the specimens. The thermal conductivity is then given by

kK = M . _£

2A AT

( 1 )

where AX is the sample thickness, A is the area of the metered section of the

main heater plate, and aT is the steady-state mean temperature difference across

the specimens. The absolute temperatures and temperature differences are

measured with type K thermocouples.

The accuracy of the k results is dependent on the accuracy of measurement of

the parameters shown in eq (1) and on establishment of unidirectional (vertical

in this case) heat flow in the metered area of the specimens. The inner-guard

heater plate is controlled at the temperature of the main heater in order to

minimize radial heat flow in the metered area. Somers and Cyphers (1951) and

ASTM C177 indicate that when the diameter-to-thickness ratio of a specimen is

greater than four, the errors in k due to edge losses should be less than 1%.

The metered diameter of the foam specimens was 10.2 cm and the thickness was

2.54 cm.

The most difficult parameter to determine is the specimen temperature difference (aT); aT averaged 10 K for PU32 and 25 K for PU64 and PU96. The

- 21 -
correctness of aT measurements depends on pi ate-to-specimen thermal contact, on

unidirectional heat flow, and on thermocouple calibration and referencing sources

of error. The diverse materials which can be tested in this type of system cause

a wide range of pi ate-to-specimen contact situations. Tye and Spinney (1976)

found that embedding the thermocouple wires in the specimen, as opposed to the

measuring plates, resulted in higher calculated conductivities. This effect is

due to better specimen-to-thermocouple contact which results in smaller measured

AT and larger k (eq (1)). They also found that the effect of thermocouple placement was dependent on the conductivity of the specimens. As the conductivity of

the specimen increases, the relative effect of an air gap in the specimen-topi ate interface becomes larger.

Thermocouple placement used in obtaining the data reported below consisted

of cementing the wires into machined grooves in the measuring plates (plates adjacent to the specimens shown in figure 7) so that the thermocouples were flush

with the plate surfaces.

The accuracy of measurements made with this system on fiberglass and fiberboard reference materials is discussed by Smith, Hust, and Van Poolen (1981). In

a qualitative sense the pi ate-to-specimen contact should be similar for lowdensity foams and the fiberous materials tested by Smith, et al . Based on the

percentage errors given by Smith, et al . for each parameter in eq (1) and the

magnitude of these parameters for the PU foam experiments, uncertainties in the

PU foam data (k) are estimated to be 0.2 mW/m.K random and 0.4 mW/m*K systematic

near room temperature; near 80 K the random and systematic components are

0.1 mK/m*K.

The specimen environment throughout the testing period was dry-nitrogen gas.

The gas surrounding the specimen was maintained at a slight positive pressure of

260 to 660 Pa (2 to 5 mm Hg) relative to atmospheric pressure. The plate emittance was 0.82.

- 22 -
Thermal conductivity as a function of temperature is shown in tables 6 and 7

and in figure 8. Each number given in tables 6 and 7 represents an average of

three or more determinations of k(T); the determinations were separated by a minimum of 15 minutes.

Table 6. Average thermal conductivity as a function of average

temperature for a 32-kg/m^ polyurethane foam.

T

(K)

k

(mW/m-K)

T

(K)

k

(mW/m-K)

95.10 11.4 256.76 22.6

106.89 13.0 258.17 22.8

120.39 14.6 264.67 21.6

132.04 15.8 270.65 20.4

153.89 18.2 274.67 20.1

169.54 19.9 275.74 19.9

175.29 20.7 280.78 20.0

185.78 21.7 284.90 20.5

202.20 23.1 290.79 21.2

214.63 23.8 297.00 21.6

216.82 23.8 297.95 21.8

220.54 23.9 301.97 22.2

239.67 23.8 318.03 24.5

239.91 23.8 332.38 26.2

248.97 23.6 332.94 26.0

340.22 27.8

- 23 -
UJ

DC

<

DC

UJ

CL

LU

- 24 -

Figure

8.

Total

apparent

thermal

conductivity

of

fluorocarbon

blown

polyurethane

foams

of

nominal

densities

32,

64,

and

96

kg/m3.
Table 7. Average thermal conductivity as a function of average temperature for

64- and 96-kg/m3 polyurethane foams.

64-kg/m3 specimen 96-kg/m'* specimen

T (K) k(mW/m*K) T (K) k(mW/m*K)

99.67 14.1 99.65 16.3

107.10 15.0 107.76 17.5

139.11 18.5 139.01 21.2

169.15 22.0 169.10 24.6

199.48 24.6 199.49 26.6

219.61 25.1 219.64 25.7

229.69 25.3 229.71 24.8

239.86 24.6 239.86 23.9

254.97 23.7 254.90 24.1

270.39 21.2 270.40 25.5

280.16 21.4 280.07 26.6

290.24 23.0 290.15 27.6

305.77 24.8 305.71 29.3

305.78 24.9 330.40 31.4

330.18 27.2 330.62 33.4

351.19 28.3 351.24 34.1

Thermal expansion - The apparatus used to imake the thermal expansion measurements presented below was developed to allow large specimens, which may be

inhomogeneous and/or anisotropic, to be studied •

A schematic of the dilatometer is shown in figure 9. Operation of the

system involves reflecting a laser-light beam onto a mirror inside the environmental chamber. The mirror is balanced on tripod fulcrum points with two points

resting on a reference material and one point on the specimen. As the relative

lengths of the reference and specimen materials change with temperature, inclination of the mirror changes and the reflected beam is deflected. The beam deflection is sensed with a photocell. This deflection can be related to the relative

change in lengths of the specimen and reference materials.

The invar hang rods, which support the specimen-reference-mirror group,

change length as the system temperature profile changes. Small corrections based

on temperature measurements along their length are made in the analysis of the

- 25 -
Displacement Transducer.

CO>

c

- 26 -

Figure

9.

Schematic

of

dilatometer

developed

for

inhomogeneous,

anisotropic

materials.
data. A small correction due to the temperature dependent change in length of

the reflecting mirror is also made.

The thermal environment is established by balancing joule heating from an

electrical heater surrounding the specimen-reference-mirror group and refrigeration obtained from either liquid nitrogen or liquid helium in the cryogen dewar

(fig. 9). The electrical heater, not shown in this figure, is wrapped on a

right-elliptical cylinder made of 1/8 inch copper and situated around, but not

touching, the specimen or reference. Temperatures along the length of the 10 cm

specimen can be maintained within a few millidegrees for a minimum of an hour.

The results of a calibration test using two reference materials, OFHC copper

(Kirby and Hahn, 1975) and fused-silica (Kirby and Hahn, 1971), indicate that the

total error in measuring the thermal expansion of OFHC copper relative to that of

fused silica was +5 pm for a 10 cm OFHC specimen. The 2a random error for this

calibration was +3 pm.

Experimental values of thermal expansion for the polyurethane foams are

shown in figures 10, 11, and 12. Discrete points represent the experimental data

and the solid curves result from three-term, second-order polynomial fits to

these points. The reference material was OFHC copper in the tests on PU32 and

PU96, and fused-silica in the tests on PU64.

Polynomial coefficients, obtained by least squares, are listed in table 8.

The polynomials are of the form

3

( 2 ) i=l

- 27 -
DELTA

L/L

o.ooi

Figure 10. Thermal expansion of a 32~kg/m^ polyurethane foam specimen.

Experimental data are represented by discrete points and the solid

line represents a three-term polynomial fit to these data. The

reference temperature is 281.99/ K.

- 28 -
DELTA

L/L

*10

TEMPERATURE, K

Figure 11. Thermal expansion of a 54-kg/m^ polyurethane foam specimen.

Experimental data are represented by discrete points and the solid

line represents a three-term polynomial fit to these data. Ihe

reference temperature is 295.180 K

- 29 -
DELTR

L/L

TEMPERATURE, K

Figure 12. Thermal expansion of a 96-kg/m^ polyurethane foam specimen.

Experimental data are represented by discrete points and the solid

line represents a three-term polynomial fit to these data. The

reference temperature is 292.227 K.

- 30 -
Table 8. Polynomial coefficients representing the measured thermal expansion of

32-, 64-, and 96-kg/m^ polyurethane foams. Reference temperature is

293 K.

Coefficient PU32 PU64 PU96

A

x -1.1825396 x 10

-2

-1.1348273 x 10‘ 2 -1.1727014 x 10" 2

A

2

1.0877846 x 10' 5 2.3112134 x 10' 5 1.4204079 x 10" 5

A

3 1.0062071 x 10‘ 7 5.3307753 x 10‘ 8 8.8122390 x 10‘8

The constant terms, A^ , have been algebraically shifted to reference the fitted

data to 293 K. Adjustments to the original constant coefficients were -7.56

x 10" 4

, 1.19 x 10‘4, and -5.09 x 10~ 5 for PU32, PU64, and PU96 respecti vely.

The coefficient of thermal expansion (CTE) is given as the temperature derivative of Delta L/L and is of the form

3

CTE = (i-D A i T

(i ' 2)

(3)

i=l

Tabulated values of Delta L/L and CTE, obtained using eqs (2) and (3) and the

appropriate coefficients from table 8, are given in tables 9, 10, and 11.

Composite curves of Delta L/L and CTE for the three foams are given in figures 13 and 14.

Mechanical properties - The tensile, compressive, and shear properties of

the polyurethane foams were determined using the test fixtures shown in

figure 15. These fixtures consist of concentric overlapping cylinders and operate on the principle that capacitance between the cylinders changes as a function of overlapping areas (Reed, Arvidson, and Durcholz, 1973). The systems were

specifically developed for use with soft viscoelastic materials such as expanded

plastic foams.

- 31 -
DELTA

L/L

TEMPERATURE, K

Figure 13. Results of three-terrn polynomial fits to the thermal

32-, 64-, and 96-kg/m^ polyurethane foam specimens,

temperature is 293 K.

expansion of

Reference

- 32 -
V

Figure 14. Coefficient of thermal expansion rel ationshi ps resulting from

temperature derivatives of three-term polynomial fits to ther ial expansion data of 32-, 64-, and 96-kg/m^ polyurethane foam

specimens.

- 33 -
Tensile Compressive

Load

RIGID FOAM SPECIMEN ASSEMBLIES

Shear Tensile Specimen

Figure 15. Extensometer systems which utilize the capacitance of concentric

cylinders. Uniform and reduced section tensile specimen geometries

are also illustrated.

- 34 -
Table 9 . Thermal expansion and coefficient of thermal expansion for a 32-kg/m3

polyurethane foam.

T

(K)

Delta L/L

(%)

CTE

(10" 6

K'

1

)

T

(K)

Delta L/L

(%)

CTE

(10“6

K"

1

)

95 -.988 30.0 200 -.562 51.1

100 -.973 31.0 205 -.537 52.1

105 -.957 32.0 210 -.510 53.1

no -.941 33.0 215 -.484 54.1

115 -.924 34.0 220 -.456 55.2

120 -.907 35.0 225 -.428 56.2

125 -.889 36.0 230 -.400 57.2

130 -.871 37.0 235 -.371 58.2

135 -.852 38.0 240 -.342 59.2

140 -.833 39.1 245 -.312 60.2

145 -.813 40.1 250 -.282 61.2

150 -.793 41.1 255 -.251 62.2

155 -.772 42.1 260 -.220 63.2

160 -.751 43.1 265 -.188 64.2

165 -.729 44.1 270 -.155 65.2

170 -.707 45.1 275 -.122 66.2

175 -.684 46.1 280 -.089 67.2

180 -.661 47.1 285 -.055 68.2

185 -.637 48.1 290 -.021 69.2

190 -.613 49.1 295 .014 70.2

195 -.588 50.1 300 .049 71.3

! 10. Thermal expansion and coefficient of thermal expansion for a 64

polyurethane foam.

T Delta L/L CTE T Delta L/L CTE

(K) (%) (10“ 6K'

1

) (K) (%) (10‘6

K'

1

)

95 -.867 33.2 200 -.459 44.4

100 -.850 33.8 205 -.437 45.0

105 -.833 34.3 210 -.414 45.5

no -.816 34.8 215 -.392 46.0

115 -.799 35.4 220 -.368 46.6

120 -.781 35.9 225 -.345 47.1

125 -.763 36.4 230 -.321 47.6

130 -.744 37.0 235 -.297 48.2

135 -.726 37.5 240 -.273 48.7

140 -.707 38.0 245 -.249 49.2

145 -.688 38.6 250 -.224 49.8

150 -.668 39.1 255 -.199 50.3

155 -.649 39.6 260 -.174 50.8

160 -.629 40.2 265 -.148 51.4

165 -.608 40.7 270 -.122 51.9

170 -.588 41.2 275 -.096 52.4

175 -.567 41.8 280 -.070 53.0

180 -.546 42.3 285 -.043 53.5

185 -.525 42.8 290 -.016 54.0

190 -.503 43.4 295 .011 54.6

195 -.481 43.9 300 .038 55.1

35 -
Table 11. Thermal expansion and coefficient of thermal expansion for a 96-kg/m3

polyurethane foam.

T

(K)

Delta L/L

(%)

CTE

(10“ 6

K"

1

)

T

(K)

Delta L/L

(%)

CTE

(10“6 K

-1

)

95 -.958 30.9 200 -.536 49.5

100 -.943 31.8 205 -.511 50.3

105 -.926 32.7 210 -.486 51.2

no -.910 33.6 215 -.460 52.1

115 -.893 34.5 220 -.434 53.0

120 -.875 35.4 225 -.407 53.9

125 -.857 36.2 230 -.380 54.7

130 -.839 37.1 235 -.352 55.6

135 -.820 38.0 240 -.324 56.5

140 -.801 38.9 245 -.296 57.4

145 -.781 39.8 250 -.267 58.3

150 -.761 40.6 255 -.237 59.1

155 -.741 41.5 260 -.208 60.0

160 -.720 42.4 265 -.177 60.9

165 -.698 43.3 270 -.147 61.8

170 -.677 44.2 275 -.116 62.7

175 -.654 45.0 280 -.084 63.6

180 -.632 45.9 285 -.052 64.4

185 -.608 46.8 290 -.020 65.3

190 -.585 47.7 295 .013 66.2

195 -.561 48.6 300 .047 67.1

This type of extensometer does not attach directly to the specimen so that

the effect of instrumentation on the experimental results is negligible. The ex

tensometer works well in cryogenic environments and is linear for large strains

(Roberts, Herring, and Hartman, 1968 and NASA, 1975). The capacitance extensometer system had a linearity range in excess of 2.5 cm when used with the tensile

specimens shown in figure 15 (5.1 cm diameter by 10.2 cm long). These specimen

geometries were used to determine all tensile properties. Foam cylinders.

epoxied to polycarbonate grip ends, 9.9 cm in length and 2.9 cm in diameter were

used to determine Young's modulus, proportional limit, yield strength, and elongation. Reduced-section specimens with gage lengths of approximately 5.1 cm, and

1.9 cm in diameter, were used to determine ultimate tensile strength. This geometry forced failure to occur within the gage length, thus avoiding a premature

failure elsewhere due to biaxial stresses at the epoxied polycarbonate grips.

- 36 -
The compression specimens were rods 2.54 cm long and 2.54 cm in diameter.

No grips were required for these specimens and therefore all compressive material

properties were determined using this geometry.

The shear specimens, 1.9 x 2.54 x 0.4 cm, were epoxied to flat plates and

each plate was attached to the tensile pull -rod system. An aluminum cyclinder

with a built-in resistive heater and thermocouple was slipped over the specimen

plates and used for temperature control and alignment during the tests.

Tests were conducted at 295 K (air). 111 K (nitrogen gas), 76 K (liquid

nitrogen), and 4 K (liquid helium). A minimum of three samples were tested at

each temperature, and in some cases several more were tested to determine material variability. Minimization of thermal shock to the sample was accomplished

by using very slow transfer rates of liquid helium or nitrogen. A given test

temperature was held for a minimum of 15 minutes prior to testing, in order to

ensure that the specimen was isothermal.

Each specimen was conditioned in an environmental chamber for at least four

days at 23 °C and 50 percent relative humidity prior to testing. Tension, compression, and shear tests were conducted using a conventional tension/compression

test machine at a strain rate of 5 x 10'3 m in“l. Preliminary tests indicated

that there was no measurable effect on the mechanical properties due to varying

the strain rate from 5 x 10"^ to 5 x 10"^ min"*.

The results are presented in tables 12 through 20 and in figures 16 through

40. The error bars on the figures show the data spread from repeated tests.

Scatter is typically higher for compression and shear tests than for tensile

tests, since the former tests are more sensitive to misalignment. Two orientations, longitudinal and transverse, are designated in the data. These orientations are relative to the axes of the bulk supplies, with longitudinal being

parallel to the z-axis and transverse being parallel to the y-axis (fig. 2).

- 37 -
TENSILE

YOUNG'S

MODULUS

(Ey),

MPa

Figure 16. Tensile Young's modulus versus temperature for a 32-kg/m^

polyurethane foam.

- 38 -

TENSILE

YOUNG'S

MODULUS

(Ej),

psi
Proportional

Limit

Yield

Strength

Ultimate

Tensile

Strength

°PL

>

MP

«

'

<>0.2%'

MPa

^ma*'

MPa

-\_

80

60

40

-20

Jo

coa

X

ffl

0.4 -

0 . 2 -

0.4-

0.2-

MATERIAL:

Polyurethane Foam

(32 kg/m 3) SPECIMEN ORIENTATION

Longitudinal

o Transverse

60

40 a

*

CM 20

b

d

0

60

40

psi

20 b

a

100

Temperature

Figure 17. Tensile test results: proportional limit, yield strength, and

ultimate strength versus temperature for a 32-kg/m 2 polyuretnane

foam.

- 39 -
30

25

20

15

10

5

0

5

4

3

2

1

0

25

20

15

10

5

0

ela stic ) | L 1 .. . . l MATERIAL: Polyurethane Foam (32 kg/mS)

SPECIMEN ORIENTATION

Longitudinal

igure 18. Tensile strain versus temperature for a 32-kg/m^ polyurethane

foam.

- 40 -
COMPRESSIVE

YOUNG'S

MODULUS,

(E

c

).

MPa

Figure 19. Compressive Young's modulus versus temperature for a 32-kg/m3 polyurethane foam.

- 41 -

COMPRESSIVE

YOUNG'S

MODULUS

(E

c

),

psi
Proportion®!

Limit

Yield

Strength

Maximum

Compressive

Strength

er

pL

,

MPa

,

cr0

_ 2%

,

MPa

MPa H60

-40

20

0

«

a

a

b

Temperature

Figure 20. Compression test results: proportional limit, yield strength, and

maximum compressive strength versus temperature for a 32-kg/m^

polyurethane foam.

- 42 -

0.2%’

w

max
30

25

20

15

10

5

0

5

4

3

2

1

0

25

20

15

10

5

0

Fiqui

ELASTIC |

TEMPERATURE. K

21. Compressive strain versus temperature for a 32-kg/m3 polyurethane

foam.

- 43 -
oeo

»«<3 'H10N3U1S UV3HS

w © m © ^ cm © * ^ (ft m vo n e5

i———

t

~r~ r

1 1 r

• • o o

o

©©

©

©

CM

O©

o

*

UJ

cc<

OC

UJ

CL

1

UJ

'H19N3H1S «V3HS

- 44 -

Figure

22.

Shear

strength

versurs

temperature

for

a

32-kg/m3

polyurethane

foam.
YOUNG'S

MODULUS,

MPR

•b

y—t

X

Figure 23. Tensile Young's modulus versus temperature for a 64-kg/m^

polyurethane foam.

- 45 -

YOUNG'S

MODULUS,

PS

I
TENSILE

STRENGTH,

MPR

Figure 24. Tensile strength versus temperature for a 64-kg/m^ polyurethane

foam.

- 46 -

TENSILE

STRENGTH,

PS

I
TENSILE

STRAIN,/'

Figure 25. Tensile strain versus temperature for a 64-kg/m3 polyurethane

foam.

- 47 -
YOUNG’S

MODULUS,

MPR

- 20.0

h 15.

0

- 10.0

5.0

0.0

Figure 26. Compressive Young's modulus versus temperature for a 64-kg/m^

polyurethane foam.

- 48 -

YOUNG’S

MODULUS,

KSI
COMPRESSIVE

STRENGTH,

MPfl

Figure 27. Compressive strength versus temperature for a 64-kg/m3 polyurethane

foam.

- 49 -

CONPRESS

I

VE

STRENGTH,

PS

I
COMPRESSIVE

STRAIN,

%

Figure 28. Compressive strain as a function of temperature for a 64-kg/m^

polyurethane foam.

- 50 -
SHEAR

STRENGTH,

MPA

Figure 29. Shear strength versus temperature for a 64-kg/m^ polyurethane

foam.

- 51 -

SHEAR

STRENGTH,

PS

I
YOUNG’S

MODULUS,

MPR

Figure 30. Tensile Young's modulus versus temperature for a 96-kg/m^

polyurethane foam.

- 52 -
TENSILE

STRENGTH,

MPR

Figure 31. Ultimate tensile strength versus temperature for a 96-kg/irP

polyurethane foam.

- 53 -
TENSILE

STRAIN//.

- 54 -
TRESS

,

MPA

- 55 -
YOUNG'S

MODULUS,

MPR

Figure 34. Compressive Young's modulus versus temperature for a 96-kg/m0

polyurethane foam.

- 56 -
COMPRESSIVE

STRENGTH,

MPA

Figure 35. Compressive strength versus temperature for a 96-kg/m^ polyurethane

foam.

- 57 -
PROPORTIONAL

LIMIT,

MPA

Figure 36. Compressive proportional limit versus temperature for a 96-kg/m^

polyurethane foam.

- 58 -
YIELD

STRENGTH,

MPR

Figure 37. Compressive yield strength versus temperature for a 96-kg/m^

polyurethane foam.

- 59 -
COMPRESSIVE

STRAIN,/'

TEMPERRTURE,K

Figure 38. Compressive strain versus temperature for a 96-kg/m^ polyurethane

foam.

- 60 -
Figure 39. Compressive stress versus strain for a 96-kg/m^ polyurethane foam.

- 61 -
SHEAR

STRENGTH,

MPA

Figure 40. Shear strength versus temperature for a 96-kg/m^ polyurethane foam.

- 62 -
Table

12.

Summary

of

tensile

test

results

for

a

32-kg/m 3

polyurethane

foam

(average

values).

in

oi—

I

cr> CO

ir> cn

• 10

CM

I

i/c 10

1^.

O o (XI I

CO

#\ o*\ CO CVI

r-- r- CO CM

lO «d- CM .—I

oo oo O <Ti

t n t"- in o to

cn oooo

. . o o

o.... o o r-~. o i"- CM CM CM CM

o o CO CO

LO CM <3

- LO 00 . . . A 1 CO

CO f—

I

r-. lo o o o OO O OO

pH ' '

-

• • • . r—

1

1 1 i i CM CM CM CM

pH r—

1

r—

H

«—

1

00

co OO LO

. . co

'd- CM . • CM i—

l

o o

. ^-x -—..—

.

o o r-H r^ LO CO CO LO

CO LO r-H oo •=3- CO o • • . . . . CO r-H CO 00 LO CM

pH pH CM r-H CO <—

I

LO LO

LO V ' w w"—

-—'

H LO LO o LO LO

OO • • • • • • CM r-H LO lo LO O CO LO CO CM LO LO o LO

LO CM lo LO CO LO LO pH pH

• • H O CM rH 53- CO

oo • • . . . . pH o o o o o o

*C

c o

CD •!“ E 4-> •r- (O U 4-> CD C

CL CD 00 -r-i. o

CDin

S_CD>

ooc

(O

s_

4->

l/l • a

^—

V

CD Cl i

1/5 •|— r—

~

#* CO 3 CO -C • 1

c c

r— Q. -M * N 07 Tj •r- •r— 3 r— V cn +-> C Cl T3 T3

“O fO c CD CD 2: S- 3

o c <o <D L0 1— +-> 4-> s: ^ X o Cl. s_ 4— ^—

V

OO •r—

i

>> •1— •r— +-> 4— •1— CD -c o CJ r— CJ u r— CD

(O +-> to CO 4-> oo O to +-> CD f— *n (TJ •r— •p (C3 C

•r— i. — CL S- #» CL (D CO r— 4-> +-> +-> +-> 4-> 4-> o

<D cn N-—

o +-> T3 V E 3 • r— to to o to CO O r—

CD CL c Q. •i— i

CM •r— CD </5 fO CO 1— <T3 fl3 1—

+-> o 3 ro O E CD • 03 +-> S- C r— r— r—

(O S- o Cl. s_ •r— •r— o Q_ r— +J CD UJ D. LU Cl • • s: Q_ >- Cl >- 3> oo 1— K

- 63 -
Table 13. Summary of compressive test results for a 32-kg/m3 polyurethane foam

(average values).

Material

Property

Specimen

Orientation* 295 K 111 K 76 K

Young's Modulus, L 8.48 (1,230) 14.88 (2,160) 13.26 (1,920)

MPa (psi) T 6.03 ( 880) 6.69 ( 970) 6.40 ( 930)

Proportional L 0.067 ( 9.70) 0.079 (11.47) 0,152 (22.03)

Limit, MPa (psi) T 0.073 (10.63) 0.150 (21.75) 0.118 (17.14)

Yield Strength L 0.114 (16.57) 0.146 (21.15) 0.204 (29.60)

(0.2% Offset)

,

MPa (psi)

T 0.109 (15.80) 0.179 (26.04) 0.172 (24.98)

Maximum Compressive L 0.287 (41.62) 0.311 (45.12) 0.338 (49.02)

Strength, MPa (psi) T 0.218 (31.60) 0.247 (35.91) 0.227 (32.93)

Compressive Strain, %

El astic L 3.3 1.9 2.5

Plastic 4.4 12.4 9.4

Total 7.7 14.3 11.9

El astic 3.0 3.4 3.3

PI astic T 5.4 10.5 15.2

Total 8.4 13.9 18.5

*L: longitudinal; T: transverse

Table 14. Summary of shear strength test results for a 32-kg/m3 polyurethane

foam (average values).

Test Specimen Shear Strength

Temperature, K Orientation* MPa psi

295 L 0.217 31.47

T 0.217 31.43

111 L 0.266 38.62

T 0.219 31.74

76 L 0.242 35.14

T 0.225 32.65

76** L 0.241 34.95

T 0.216 31.39

*L: longitudinal; T: transverse

**Test conducted in LN2

•

- 64-
Table

15.

Summary

of

tensile

test

results

for

a

64-kg/m 3

polyurethane

foam

(average

values).

o o CO CM O e-~ A A

i-H ^

iX) O in

• . CO CM

co

LO CO

CM CTi

. . CM COoi

00 00

CO co

1—1 CO

I LD o LO o o o . o CM CM

*—i o

CO

o o c- in

--I o

cr>

co «=r CM CD

r^. e-^ co o

e-- co

e-. o

co I cm co

cm e-.

CD.... O CD CO O CO

i—I i—I CM CM

co

CO CM T—I O

o o cti e'- en e-'

ft ft 00 CO

in cm

CM O

CD CO

in cm1

CO CO

D~- o

r—I 00

CO 00

in e--. <—i o 1—1 CO

. . i—i o

00.... O 00 CO O CO

,—I 1-H CM CM

|

o o CO CM O CO CO ^ cm e-" t—

1

CO CM 00 in co • • LO o . . . . =3- co

ft ft CO CM d- e'- <Ti

<3- CM CM en co r—l in - ^ ^ - ^ '—

* '—

<—

1

CM CO CO o CO

CD • • • • • • CM CD CM CTi D" CO o in co CO CO CO CO o

O CM i-H in O co CTi t—

H

. . CO .—

1

CO CM CTi CO

i-H . . . . • • CO 1—1 o o o o o o

e -t-> •r- 03 U 4-> (U c

Cl CL) 0O -r-s_ o

i

I

I

I

I

<l> co

SO)>

COc

03

5- +3

A

10 i

3 oo -C *1

1

CL 43 —

3 r— '

CD +3 O 03 C 0) o C 03 CD CO s

^

O Q- 4— ,—

1

>) * r~ •r- 2: +3 4_ T03 +3 oo co +-> 00 O lO

• r— S- - Ol S- *> CL

1_ <u CT) O -(-> -O &S- —

0) Cl SZ Cl *i

r- CM

+3 o 3 03 O E (U • 03

03 i- O Q- S_ -r- •r- o o_

o_ >- ^ O 1

co • A

<L> Q. r— i—

A 03

•r— c C

CO 03 •p— •i

c CL 03 O

OJ S 3

1— +3 +3

A OO • r—

CL) SZ u o t— U o r— CD

4-> +3 CL) -r- •1

03 -r— •1

03 C

03 CD r- +3 +3 +3 +3 4-> +3 o

E c •r— CO CO O co (/) O i—

•i— <1) CO 03 03 1— 03 ro 1—

+-> S_ C i— r— r— r—

r— +3 CD LlI Cl LU Cl. .

.

CD OO 1— _i*

65
Table

16.

Summary

of

compressive

test

results

fora

64-kg/m^

polyurethane

foam

(average

values). 0 0 00 CM LO r-H CM

r-H CM cr> r^- CM

O CO LO • e 9 9 9 9

9\ 00 LO 03

O CM

O 00 CO r—1 LO cm r-- p*- cm

r-t 1—1 1—! 1—1 1—1

LO LO r-H

O ^ Cj" ^—

v > — >— * © © • e • r-H r*—•

03 CM

v

—1

CO

CO 00

O 'd- <—t CO 03 CM \—1

r-H 03 CM 00 O'- CO 00 co • * CO CO 00 '3- 1—s CO CM >vf * • • e 9 9 (33 9d" 0 0 0 0 r-H 0 __ __ O O t—1

*dp co 0 LO CO

CM 00 LO LO p-. r-. co OO © * e • • •

©\ #v 03 1—1

CO 00

CM CM i—1 LO CO P" LO rH

r—1

T—1 t-H »—1 r-H ^ r^r. r-H LO CT> CO v—xv

--

V c v

/ V e © • • • • p^. t—h

r*^ 03 LO r-H CO CM >=d- LO CO CO 00 r-H 03 1—1

CM LO lo 00 . . CO CO 03 LO 1—1 r^s. •M- . • 9 9 • • 00 *-h O O O O H O __ 0 0 CO LO r- lo 0 co CM OO Op LO co O- CO

CO LO . • . . . . a a CO CM O'- ! 1 lo

CO rj- 03 LO r-H CO LO

O 1 r 1 !—H <-H 1—1

CM

O CM co LO co 1 1 v 

- >—

s • • • • • • T 1 < 1 (J) O OJ t-H

t—

H r-H

O 03 CM I—1 CO cn *“H r-H cn cm p-- co \—1 CM 00 CM e • CO CO co O C- CO I 9 9 . . 9 9 CT> CO 0 0 0 0 r-H O 0 0 <

1 5^- "Jd" 1—- CO CM

cn i->. CM CO P-. co 93- LO

f—1 T 1 9 . . . 9 « A A LO O r-H *3- P^ CO

CO 1—t

LO CM p- co 03 LO

un

v

—

r

v

—--r.

-- >—- *—

O LO LO LO CO OO 1 03 • • • • • • CM 03 1—1 CO lo Co- CM 03 CO CO co CM

co 0 00 *3- en co C^ CO . . CO l-H 9d- CM CO CO

<—1 00 9 9 . . 9 9 CM 0 0 0 0 O O *C

c:

O

OJ *1— a; £ 4-> LO • r— fO s~ O 4-3 _J f— _l 1— _j l— _! C- _J 1— as

CD c >

CL <D 03 1 CO •r— c

CO

O +J

a>

— #> h-” > -r- c • 1— LO • f— • A

a

r

—.

LO CL. SO r—

co •r— S- CO 0 LO 0: •> O) +-> c

r— Cl +-> S— rts LO • 1

O p— *—-- 03 4-3 CL CL ~o a ra SO CD E S a> rs 0 C 03 CU LO O > 4-3 s ---> 0 O- i- M— „

C_) « •(-— •r— 1 >> 1— •r- s: 4-> 4- -r- JZ LO O O ,— O U r— 03

rO +-> CO LO 4-3 L/3

O LO E 4-3 LO -r— -i— fO •r— •r— H3

C

•r— S- - Cl i- •> cl

O 03 a> +-> +-> H-3 +-> +-> -M

O

£- O) 03

—

O 4-> "O E 0 S_ LO LO

O CO 00C 1—

0) CL

C O.T- i— CM ai

a id its t— CO (O h-

•M 0 O CO

O E a) • icX s- E 1— 1— t— r—

ro sO Cl. s_ -i- •1- 0 a~ ••0 +->

O LU Q. LU Cl. • 9 21 Q. >- r 0 1 >— 21 00 O _J

•*c

66
Table 17. Sunmary of shear strength test results for

foam (average values).

a 64-kg/m^ polyurethane

Test Specimen Orientation* Shear Strength

Temperature . K MPa psi

295 L 0.508 73.57

T 0.668 96.92

111 L 0.706 102.41

T 0.741 107.47

76 L 0.724 104.91

T 0.709 102.75

4 L 0.672 97.36

T 0.874 126.74

*L: longitudinal; T: transverse

- 67 -
,—

- r^- OJ CO P^- CM

<D o • • OO CO CM o CM 00 «—l

to CO r-H OO r-H i 1 • r 'O' 3> i 1 i 1 LO CO

i-H LO i 1 i 1 CM CO

00 rH i 1 CM CD • • • • lo LO CM rH ^f o • r—1

i—

H

r

—-» to

<u

r

^

33

r—

x

LO CO

r— r—1OJ

O o rO LO LO • • > OO LO r—1

#v #» r-H CO

OJ LO OJ 00 CM

CO rH rH i 1 i 1 —

r

r

rO to >—

v—" i 1 i 1 CM CO

s- p- LO o i 1 i 1 C-~ 03

0) «—1 o i-H LO > • • • • ro LO CO CM rH —

O 00

rH E

03O4- •—-- -—

LO

CD +—

p

03 CM

C LO • • 03 <D <d CM to -C <d CD CD LO

+-> r* CM CM

CD r-H i 1 i 1 v

—

S- f“H T—1

r-H i 1 i 1 o 13 rH ' ' " i I i 1 CM to

>3 rH r^.

O Cr- f— • • • • o OO OO 00 rH

CL o 00

r—1

COE\CD *—

4* " / s r

—>

** 1 r-H D CD CO ^ -V to s -—X o <d 00 CO r^. CD CD • • • • • • r-H O- LO CD <D ’=3- CD

03 CO <D LO r-H CD

O h>. rH OJ v—H

S_ LO

—

—v

V ^ V ^ V

H o 03 ^ 

^ 

OJ CD

4- CM LO i—H

rH OO LO rH CO

LO LO 00 LO OJ

to • • • • • • • • 4-> O LO o o o o r-H rH r— LO CO 3

to

CL) s- *c

4-3C o

to CL) •r— OJ E +-)

4-3 •r— 03

CJ 4->

—

J

h- _J f— -J h- -J ha> CL) C ,

CL CD

•i

OO •r— to S- c o

CL) 4-> 4—O

>3

S03 OJ E (

E •f— 23 —V

in 40 r— 4-> c

.33 0) 0) C in 1— • r— >3 ^ «s o -—V

4- ^ •N yV CO X) 4-3 • i— r- •r— JZ 4— •!— CD -C •r— rH • r

L_ in to in 4-> in 4-3 o to 4-J 4-3 cn

S- CD

— 13 CL i_ *> CL CD CL C3 CD CL

CL) CD CL CJ>

O 4-> -O c E C

V " r—

4-3

O

C C3 CL-i- r- CD CM •r— CD jO 03 L- =3 a (a O E fO CD S- • <0 4-3 C- rO

03 OO o Q. S_ -r- CL *r~ 4->O CL , 4-> CL

1— >- s; :e

O 1 >- OO ^21 ZD OO )I

00 o 00 00

O 00 • • • • • • rH t"H r—I CO r-H ffI

r-H

O 1-H 00O 00 • • • 0 • • OsJ O CV t

i CO rH o o o LO O LO • • • • • • cvi o CM CM O CM fI o o o LO CO CO • • • • • • ro LO oo CO to CO fII

CD * O

U CJ CJ 1 c •i— «r— •1— • 1

•r— •r— 4-3 4-3 i3-3 r—

in fO to to ro to co ro c s- fD X) 4-3 ro ro 4-3 CD 4-> ,— i

O i— ,

O

f— 00 LU Q_ LlJ cl 1— - 68 -

*L:

longitudinal;

T:

transverse
Table lq.

Summary

of

compressive

test

results

fora

bfi-kn/rr 5

polyurethane

foam

(averaqe

values).

vrc-Ke e o

<L> -r- E 4-> I- TO U -M

a> e

o- cl

C/O -r-ec „—, . —. - ^—

- -

..

— cr CO CO LD

CM CO CM cc LD CV o • • • • • • CM ld CO CO cc o *sj" CO o VC in cr CO LD

CO o CO CM CO CO CO r < r-H > „ >W- -— **— *

CO oc t—H • • • VC LT> f—H

CO r-t LT LD *H rH C- a r- O r— ?-H

oc c cr • • • • • • • * rH CV CV »H cv cv CM cv a r^-

\n ur o f—

H

VC CT> cv <x o cr oc VC LC CV • • • • • • CO CO r^ CO LD VO cr. * o r-H cr

c: cc CM CM CO cv CO CO

»—i —

'—- —

•

"

r-> VC CO ^ ,, > - • • • c f—H

ld cc cv CM VC o

CO CM

O o o CM r-H T—

H

CO r-H cr r- • • • • • • • • « 4 f—H

T—1

cv f-H cv CV

co • • CO VC

CM

cr

CM VC • • ^ *d"

co

cr

vn „ * ^— a oc c f-H VO cr CO cc a • • • • • • c CO r- cr CM cc o r-H CO cr o VO CO

f-H cr r— CM CM CO CM CO CO f-H r- CC LO CM r- f—1 ^ _ w - «*, - . - • • • • • • r-H «rr CO r~- «^r vo cr. o f-H CO cr LD vr cr VO c VO o cc vr CM

CM i—

H

f-H f—

H

CM f—

H

CM CM

VC VC

_ ^ . r-H o CO CC CC r-H ^—

—

CM CM cc VC »—

H o

CM cr • • • • • • a LD f—H

CC cr cr cr

f—

H

r-H cr CM o CM

#\ #\ f—

H

f-H f-H r-H VC CO -

’—>

vc «d- cr f—H LD ocr • • • • • • CM cr cr CO c CO CM VO ^ cv VC

f-H cr CM CO CO cr cr cr cr r- VO VC cc VC a oc ccCM

cr. CM i to

a;e •> c. _E

4-5 E 4-5 <C a> c cr

a) c co CJ> E >

jr- >.. .—

o ^ 

M— CL •r- sr

'«o 4->

r • r- • r“ •r

JO <+- •P— CL’ E • r- co

V,— S- CO CO CO +J VO 4-5

O CO 4-5 4-> CO co •>

O (J

a <_> s- <u — 3 a •> a cr. Q. <T3 OO Cl a- e •r— •r— •r— »r— ai a c r— o ^ — c E >—

E n - E -r- 4-5 4-> r— 4-5 4-5 f—

+-' o E 3 a •i

f—C

V CM •r- CL

G f«3 to CO tv to CO tv

(O s- 3 T3 03 o E TO a> E • fV +-> > <T3 E E CO fO 4-5 tv tv 4-> z: o_ O O CL

4- •i- a. f— 4-5

G CL r— •r—

D

O 4-> f— r—

O f— f—O

>- ^:

Cv.

—i s: >- CO ^r. =D CO IET

G OO UJa 1— VjJ CL 1— - 69 - 1

onni

tudi

nal;

T:

transverse
Table 20. Summary of shear strength test results for a 96-kg/m3 polyurethane

foam (average values).

Test Specimen Orientation* Shear Strength

Temperature, K MPa psi

295 L 0.846 122.70

T 0.893 129.54

111 L 1.114 161.58

T 1.109 160.85

76 L 1.025 148.59

T 1.118 162.15

4 L 1.064 154.38

T 1.020 147.99

*L: longitudinal; T: transverse

Discussion of Results and Modeli ng

Thermal Conductivity - Heat is conducted through a foamed material via solid

and gaseous conduction, by radiation, and by convection. Skochdopole (1961) has

shown that convective heat transfer will not occur in cells whose dimensions are

less than 3 mm. The cells of undamaged polyurethane foam with density of 32 kg/m^

or greater are at least a factor of three smaller than this threshold size. The

foams studied here have cell dimensions smaller than 0.5 mm (see table 1). The

convective mode will therefore be ignored in the remaining discussion. It is important to keep in mind that if cracks develop in the foam, either due to thermal

or mechanical stresses or debonding, convection can become a dominant mode of

heat transfer.

Radiant heat flow through foam insulation is due to both transmission and to

absorption and reradiation. Resins used for making foams are partially transparent in the 2 to 30 ym range of wavelengths (Skochdopole, 1961). Sections

associated with thermal insulations are normally optically thick

(thickness >> photon mean free path), however, so that direct transmission will

- 70 -
be small. The effective conductivity due to radiant heat transfer (k r ) can be

estimated by

k

p

= 4 aei T

3

(4)

-8 -2 -4

where o is the Stefan-Bol tzrnan constant (5.67 x 10" W*m~ K~ ) , e is the emissivity of foam, i is the cell dimension parallel to heat flow, and T is the temperature of the warmer side of the specimen.

Solid conduction (k s ) takes place through the cell walls and membranes of

the foam. Since PU resins are disordered (noncrystall ine) insulators, heat is

transported by lattice vibrations (phonons) and is nearly a linear function of

temperature. The relationships describing the solid conductivity of the foams

tested here are

k

s = 0.90 + 0.0190 T for PU32,

k

s = 3.08 + 0.0172 T for PU64, (5)

and k

s = 4.36 + 0.0278 T for PU96.

Temperature is in kelvin and thermal conductivity in mW/nvK. The steric factors,

which arise due to elongation of cell axes parallel to the direction of heat

flow, are included in these relationships by virtue of their experimental basis.

The remaining mode of heat transfer is conduction through the gas (kg) occupying the foam cells. Figure 41 indicates the conductivity of gases sometimes

found in insulating foams. When a mixture of gases is present, kg can be estimated by

k g

" ^mixture 2 X

i k

i

i =1

- 71 -
THERMAL

CONDUCTIVITY,

mW/fm-K)

TEMPERATURE, K

Figure 41. Thermal conductivity as a function of temperature for gases commonly

found in polyurethane foams (Touloukian, Li ley, arid Saxena , 1970).

- 72 -
where thermal conductivities of the individual species are given by k-j , X-j

represents the corresponding mole fraction, and n is the number of species present. The k-j are temperature dependent and, as seen in figure 41, are nearly

linear functions of temperature. The gases present in PU32, PU64, and PU96 are

CCJI 3

F and air. Their conductivities can be approximated by (Touloukian, Liley,

and Saxena, 1970)

k rr „ c = - 4.1 + 0.04 T, 250 < T < 300 K CCjj^F * — —

(7)

k . = - 0.661 + 0.103 T - 0.469 x 10

' 4

T

2

, 100 < T < 350 K dir

in units of mW/m*K. Total gas conduction is given by

k g

= X CC£

3

F

k

CC£

3 F + ( 1 _XCU3

f)

k air ^ 8)

Harding (1964) indicates that the values predicted by this simple molar mixing

approach tend to be slightly higher than those computed using kinetic theory

(Tsederberg, 1965).

Although it is not rigorously correct to add the modes of heat transfer

(they are not independent of one another), the total apparent conductivity (ky)

obtained using this approximation is acceptable for polyurethane foams (Gorring

and Churchil 1 , 1961)

.

k

T

= k

g + k

s + k r (9)

For temperatures near ambient, only gases exist in the cells and ky can be estimated using eqs (4), (5), ( 8 ), and (9) when

p is known. If partial

pressures are also known at T-j, eqs (10) and (11) can be used to determine

X CCZ 3 F’ rat ^° Part ial pressure to absolute temperature (eq 10 ) is

constant for each species to the extent that they approximate ideal gases.

p cc*

3

f,t

rpair,T

PCC*

3

F.T

i

< T > /T1» T> T

c

- P air,T.( T >/ T

i’

T> 100 K

(10)

- 73-
and

(ID

At temperatures less than or equal to Tc condensation of CCJI3F occurs and the

partial pressure of CCJI3F is given by

where T is in K and pressure is in kPa (the saturated vapor pressure is more accurately given by a complex relationship in Du Pont, 1979). The temperature of

initial liquid vapor equilibrium for CCJI3F (Tc ) is indicated by the inflection in thermal conductivity at Tc

= 278 K, = 275 K, and = 245 K for PU32,

PU64, and PU96, respectively (fig. 8).

The equations given above and the thermal conductivity data were used to independently determine the cellular gas content of PU32, PU64, and PU96 (table 5).

Results of the calculations are shown in table 21. The components of the total

apparent thermal conductivity were calculated using the relationships given here

and are also shown in this table. Comparison of the computed conductivities to

the experimentally observed values indicates that the rel ationshi ps for k s , k r ,

and kg apply quite well to PU32, PU64, and PU95.

Thermal expansion - Little low-temperature data exists in the literature for

Delta L/L or CTE of polyurethane. Materials which have been tested are generally

characteri zed by a nominal density and sometimes a tradename. Comparison of the

current values to the existing data base indicates that Delta L/L at 105 K for

PU32, PU64, and PU96 fall near the median with a band of approximately +20%

needed to include all of the literature values. A more quantitative comparison

is not justified considering the variation of materials involved.

The diagram shown in figure 42 indicates the parameters that can affect the

expansion characteristics. Although not indicated in the diagram, none of the

P

v = PCC£ F = 8.0875 x 10

6

/exp(3340.4/T) , T < T

c

( 12 )

- 74 -
Table

21.

Computed

values

of

thermal

conductivity

components

based

on

initial

vapor-pressure

temperatures

as

determined

from

thermal

conductivity

data.

_x

i Q.

X

a>

CL.—

X 3^

a> -

*3- o

LO

I • O'! CO

• 1 • OO o

oo co

• | • r-H O

a. • CO CTi CO O'! co LO LO o

X E • • • • • • . • a> x. rH O'! CO CO t—1 LO CO

OJ rH r-H OJ OJ \—1 OJ OJ

• X Ot *3" OJ CO o r-H t- E • • • • • • • • -X X r-H <T> CO CO r-H LO cn 3 OJ t-H r-H OJ OJ rH OJ CVJ E

rt o r-t

• • • oo oo o

CO...LO r-H

r—4 f-H (. J

LO O')

. . .-H O

• CO OJ

oo E CO OJ o OJ 00 o • • -X X • • • • • • OJ i—

H

3

E

CO CO CO 00 r*x LO r-H i—

H

• rv CO OJ o CO CT o CO E • • • • • • • • -X X OJ rH o CO OJ o •xf OJ 3 r-H t-H r-H r-H r-H rH rH r-H

+-> ca LO CO 00 Ox LO 00 O CL . • • • • • • • +-> -X OJ Cx rx. CO f—

1

Ox o CO

Q_

| X LO

1 CO LO

« OJ »-H

1

l OJ X1 X OJ *xi"

11 CO o CO

i. ca CO . • • CO • • • O'! • • •r- CL 3 O'! 00 Ox 3 <T> 00 Ox 3 00 CO

ca .x CL r—

1

T—

1

CL i-H rH CL

a. —

! X Cx o

1

1 CT <T> o

1

1 CTi CTi s_ OJ OJ o OJ OJ o CO CO

•r— . • • • • • • • ca o o r-H o o t~H o o X

u_ CO .—

00 OJ o i—

H

LT> o LT) OJ

ca . • • • • • • . O CL OJ CT> o Ox CO o OJ o o x:

Cl —

LO *xf rH

I c

<=* o<_> X

oo CO CO o IX...x O

o o o

r—H f—i CO IX...X o

o o o

CO CO

• * o o

00 00 OJ 00 LO OJ 00 LO OJ

CT X r—

H

<T X rH cn r—i OJ OJ rH OJ OJ rH OJ OJ H

75

0.00

0.0

1.00

3.0

3.0

10.3

7.5

0.1

17.9

18.0
Thermal

Expansion

- 76 -

Figure

42.

Parameters

affecting

the

measured

thermal

expansion

of

expanded

plastic

foams.
parameters are independent of one another, e.g., the blowing agent will dissolve

in the resin to some extent and will alter the resin chemistry. Viscosity will

also be affected by dissolved gases and will, in turn, affect the cellular morphology. It is instructive, however, to consider the effect of these parameters

on the observed results for PU32, PU64, and PU96.

The detailed chemical makeup of the materials is proprietary information and

is not known to these authors. Each is a polyether-based material but the specific isocyanate is not known. PU32 and PU64 were foamed as continuous buns having unrestricted freedom to rise. PU96 was poured in a form which also allowed

unrestricted rise. Additives such as fire retardants, elastici zers, surfactants,

and coloring agents are unknown as are formulation temperatures. Each of these

items can affect the chemistry and/or molecular linkages and therefore the expansion characteristics. Each variable will affect the cell structure, however, so

that the net effect of resin chemistry is reflected in the cell morphology and

strength properties. As will be shown below, the expansion characteri sties of

the resins can be calculated. In spite of all foams being polyether based and

expanded with fluorocarbon, thermal strains in the three lattices differ significantly.

The difference between the changing internal pressure and the external pressure define a temperature dependent stress on the foam. Internal pressures were

computed using the procedure discussed under thermal conductivity and are tabulated in table 22. The experimental external pressures were 89.3 kPa for PU32

and PU96, and 84.0 kPa for PU64. Compressive Young's modulus, E

c , (Arvidson

and Sparks, 1981; Arvidson, Sparks, and Guobang, 1983; and Arvidson, Bell,

Sparks, and Guobang, 1983) and this pressure stress can be used to compute a

strain. These computed strains are parallel to the direction of the experimental

determinations and are tabulated in table 22. The uncertainty of the calculated

- 77 -
CUG

G 3 -r- CM CM to CM CO

•3 tO ro p— sld- LO 00 o tO </3 G O CS O CD O r-H 03 CU -M —• • • • • • ZD G tO o o O CD o o cl c

<T3 T3

CL

C CO CO ,— rC S'-' to 03 CD d- 03 drO 0>r- IO r- d- oo O LO d- G CM C 3 CL CM r—H

03 CO d- co

g co 3 -a 03 r^. 00 to LO LO

cu zd o o^- CM CO CO d- LO to

+J Q. CO >- s c 03 G ID ,o CL cu 4- 4- G CO O 3 IO''

ro CO CU ro CM CM to LO CO to c cl CO G CL • • • • • • o -i«£ CU +-> 03 CM LO CO LO to

•1—

G 00

—

to P-- r^- oo 00 co

+j ro CL o • c cn 3 00 i— CU 4— CO G

<UC 3

ro

G

G CO ro 1—1

t~h r~- oo o o» cu to CL • • • • • • to 3 4-> O) o r-- CO LO d- CM

ro

CG

—

CM rH T—

H

to <—i Cl T3 <U

0)G

+-> =3 CU

ro to

G

C I

p^ CM CO i— to 3 •!- LO P-- CO rH CD 3 O) CO ro '—

o o o o CD O G « GJ« O • • • • • r— CL CU 4-> —

o CD o CD O <o G tO 1 1 O P— Cl

ro

GC

O

G co to

•i- CU 35 , to CO 00 00 CO oo

+-> +-> COi

— ro LO e'- o CM

U

X

G 3 CL d- CO CM en to CM

CU UJ 30^ CM 03 CO oo CO CO G o o —

CM CO

d- LO p^ 03

•(— d" >- s: a • to *—

ZD

+-> r- CL cu C 03 G CO

a>

G 3 CO '— E -r- to CU ro CO 00 00 CO 1 1 d0) 'O io ta • • • • • • G 3 CU 4-> CO d- 00 CD d- p^ 3 +-> G 00 —

r—1 LO to 1

p'- P". to -i— CL

ro 03

CU

C E O CU i— ro G

cuC 3 '—

JD

G CO ro CM CM P-- 03 to

+-> -p- CU CO CL • • • • • • t— +-> CU -3«C LO 03 CO CO 03 to o 3 C G —

to CM CM

r " 1 -m -a •—l CL oE

CU CU 1— to G

C g- LO i 1 to si- 1— — 3 •!- CO CM CO r-. te

ro 03 CO ro

—

CO d" d- co CO

S_

C CO

G yi CD • • • • • ro 3 CU +J —

o o o CD o CL O G tO 1 1 1 1 1 >- CL c

•i— T3 • IB C<J to co

U- ro VO 3 •—

CD to d- LO d- 1 1 +-> CO 03 i— to LO d- 03 CO CM 1

to CO Cl

C 3 Ol LO o CO G- LO CO

cu 3 -a CO o CD 1 1 CO d-

"O

G

G o o ^ rH t—1 rH \

1 i—i

<U 3 O CM

G S CJ to 4- CO 3 CO ZD a CU ro CL CU C G Cl G CO

•r- CLL^ t 3 CO -—

CO CU ro

O o CM to c-- CU i— o CO G Cl • • • • • * G ro • CU +J -iC 00 CD to LO O) CM 3 c d- G CO —

r—1

to to 00

00

G 00

to CU

CU +j -o

CL

G

X

G r— CU Cl CU ro ro G C 3 r—- G CO ro CM CM CM

p— <T> to • CU CO CL • • • • • • CM +J <U rH 03 CO CO to

CM

C•—< CL CM CM t—1

CU r—

JD CO o o o o o <T5 03 LO d- o in o 1— CM CM CM CM r-H r-H

78
pressure-induced strains cannot be determined from available data. Straight-line

behavior of E c (figs. 19, 26, and 34) was assumed in the temperature range from

100 to 293 K. Deviations from this behavior could be significant, especially at

temperatures far from the experimental data.

The difference between the experimentally observed contractions and the

pressure-induced strain is the thermal contraction of the resin. These computed

values are tabulated in table 23. If the pressure stress given in table 22 is

applied to the foam in the transverse orientation, i.e., the transverse Young's

modulus is used, the pressure-induced strain in this orientation can be computed.

A value for the total transverse apparent thermal contraction can then be calculated by summing the resin component and transverse pressure induced strain.

These values are also given in table 23. Figure 43 shows the comparative values

of longitudinal (experimental) and transverse (calculated) thermal expansion.

The effect of using a straight line approximation to Young's modulus at higher

temperatures is to overestimate the pressure-induced strain and thereby cause the

predicted values of resin contraction to be smaller than they actually are. The

slightly positive values for resin contraction of PU32 at 250 and 240 K are

thought to be caused by this approximation.

Thermal expansion of the resin as a function of density with temperature as

a parameter is shown in figure 44. Resin expansion as a function of temperature

can be determined from this family of curves for densities between 32 and

96 kg/m3. The second component making up the observed thermal expansion is

that caused by pressure-induced strain. This strain can be estimated from a

knowledge of internal gas pressure, external gas pressure, and E c

. The internal gas pressure can be computed, as discussed in the thermal conductivity

section, when the partial pressures are known. The compressive Young's modulus

is discussed below.

- 79 -
m

fO CO

O0ZD

Cu"Oc

<TJ

OS *sr CO

ZD

Cl

OS CM

CO

ZD

CL

4-oc/1 sco

*t

4-> O

(tS s_

4-1 • £C **

o CL) u 00

i~ 1— 0)

<T3 > e oo

S. c

<D <13 JC s_

4-> 4-1 "—

01

in •r— S- r—

<D Z3 > o00 O e E

<0

s~ oo

4-1

—Ol o c

<u Z3

+-> o

<0 >- I Z5 a O c i

<a

<13 U OlOl

O) ai s: s~ +J 4-1 Ol TDC T3

<13 d)O

1/1 Z3 C T3

•r—

C

1/1 • i

<D ! S- ai

i- 0) 3

.c Ol +J Ol

a) 4- c_ O CL C 0J o JC

r— 4-1

4-> o E

<D

O

C. s_

4-1 4— co "O o O)c

r— •f— HD E E Ss~ ai

0) 4-> _c CL) i 

o

co \5 1 CD> 03 a-£ CO 4-> ' c ,

03 <u

t- o

CO 03L 5r? o> *-> —

i> oo

l/) to

Z3

—

cn<— 03 C D Q- 3 T3 o o ^ >- 51

—J c

•r- a* ' 03 CO

]-*-> CD r- Cd

CD a

13 -r- CO 03 -—

lOL 55

-4->

cr>.

— 03

C 3 Q.

=3 T3• r— --—

J

03 to a^‘ s 1 a» —

> 03 a-* CO

Z3 •<- CO 03 s ^ L 55 C 3 Ol

Z3 “U O O

— >- 21

r— Cd

CD O • OO

C\J

CL) Sra h- 80
DELTR

L/L

Figure 43. Longitudinal (experimental ) and transverse (calculated) thermal

contraction of PU32, PU64, and PU96.

- 81 -
CALCULATED

THERMAL

EXPANSION

Figure 44. Calculated thermal contraction of polyurethane as a function of density

with temperature as the parameter.

- 82 -
Mechanical properties - The strength properties near room temperature are

traditionally represented by equations of the form

g strength property = Ap (13)

which is equivalent to

log (strength property) = A' + B log (density)

(Hilyard and Young, 1982; DuPont, 1979). DeGisi and Neet (1976) found that B

= 1.75 for both compressive strength and modulus, and that A' (A

1 = log A) was a

linear function of temperature. Their formulation was limited to T _> 298 K for

strength and T >_ 219 K for modulus for materials in the density range 153 to

392 kg/m^. Cell size and orientation were not considered in developing their

empirical relationship. Menges and Knipschild (1982) present several theoretical

developments for strength properties based on various assumptions concerning cell

shape and orientations. None, however, have addressed developing relationships

describing the strength behavior of foams as functions of temperature at cryogenic temperatures. The strength data and the characteri zation of cell size and

shape reported here was intended to allow this possibility to be explored. A

model, based on fundamentals and the current data and which would allow predictive capabilities for the mechanical properties, has not yet been established.

The behavior of the compressive Young's modulus (figs. 19 and 26) and the tensile

strength (figs. 24 and 31) in the temperature range 76 to 111 K was particularly

difficult to incorporate into a model based on current understanding. An entirely empirical approach to establishing a predictive capability was therefore

adopted. As is the case with all such relationships, the extent of its applicability to other polyurethane foams will be established through experience. Figures 45 through 48, eq (14), the height-to-width ratio of the foam cells (H/W),

and the foam density can be used to estimate average moduli and strength in

- 83 -
100

90

80

70

60

50

40

30

20

10

3

gure

i 40 50 60 70 80 90 100

DENSITY, kg/m3

45. Young's modulus of polyurethane foam in tension as a function of

density with temperature as the parameter. The modulus obtained here

must be modified by a function of (H/W) for a specific material.

- 84-
TENSILE

STRENGTH,

MPa

DENSITY, kg/m3

Figure 45. Strength of polyurethane foams in tension as a function of density

with temperature as the parameter. Strength obtained here must up

modified by a function of (H/W) for a specific material

.

- 85 -
60

55

50

45

40

35

30

25

20

15

10

5

ure

DENSITY, kg/m3

. Young's modulus of polyurethane foam in compression as a function of

density with temperature as the parameter. The modulus obtained here

must be modified by a function of (il/W) for a specific material.

- 86-
COMPRESSIVE

STRENGTH,

MPa

30 40 50 60 70 80 90 100

DENSITY, kg/m3

Figure 48. Compressive strength of polyurethane foam as a function of density

with temperature as the parameter. The strength obtained here must

be modified by a function of (H/W) for a particular material

.

- 87 -
tension and compression. The temperature range is 76 to 295 K and the density

range is 32 to 96 kg/m3

. DeGisi and Neet (1976) found that crosslink density,

urethane to urea bond ratio, and type of isocyanate had no significant effect at

temperatures below about 350 K.

Factors for the direction of stress relative to the elongated cell axis are

F(longitudinal ) = 1/2 { [0.6 + 0.15 (H/W)]" 1 + (H/W)

}

(14)

F(transverse) = 1/2 [0.85 - 0.1 (H/W) + (H/W)"

1 ]

The temperature dependent values at a particular density, from figures 45 through

48, must be multiplied by this factor. This procedure produces values for the

strength properties that are generally within ±20% of the NBS experimental data.

Major Achievements (IF)

The low temperature data base for polyurethane foams has been significantly

improved with the addition of the data generated by this effort. These data are

unique in that they include all basic thermophysical properties of interest to

insulation users, and they are related to materials whose morphologies are also

known. The materials used span the range of densities usually considered for

thermal insulation applications.

Empirical rel ationshi ps and procedures were developed for predicting the

thermophysical properties of polyurethane foams at low temperatures. A minimum

of information, which is relatively easy to acquire, is needed to use with these

procedures.

Testing procedures for use on viscoelastic materials were refined. These

procedures could be adopted for general use in lieu of standard procedures which

are not intended for use at low temperatures . Revised standard procedures are,

of course, the ultimate goal in this area. A basis and need has been established

for standard materials as well as procedures.

- 88 -
Major Technical Problems (IF)

Three areas presented technical problems which persisted to the end of the

program and had significant impact on the results: meaningful characteri zation

of materials, material variability, and anomalous behavior of the physical properties.

The materials studied were obtained from commercial producers because of the

experience and expertise required to produce well designed foams. The chemical

composition and foaming parameters were proprietary and in essence, only the

polyether base could be determined. The characteri zation technique which best

addressed our needs was statistical evaluation of photomicrographs. This procedure is time consuming, and an extreme effort is required to obtain sufficient

data for statistical characterization.

Material variability was high for all materials; the concomitant uncertainties can only be assessed by large numbers of repeat measurements. Time and

funding caused compromises in this area. The variabilities themselves are of interest since they reflect what a user must expect in batch lots of foam.

The physical property data are complicated at cryogenic temperatures.

Modeling based on fundmentals was not possible due, in part, to unexplained temperature effects.

Conclusions (IF)

Thermophysical properties of foams at low temperatures are functions of temperature, cell morphology, and gas content. Empirical procedures have been developed which allow predictions of thermal conducti vity , thermal expansion, and

tensile and compressive properties at low temperatures for a range of densities.

Parameters which must be determined in order to make use of these procedures are

indicated in table 24. The empirical procedures are based on the results for

three particular polyurethane foams. Application to other polyurethane foams

must be evaluated.

-89 -
Table 24. Parameters needed to estimate the thermophysical properties of

polyurethane foams as a function of temperature.

Property

Material Parameters

Foam

Density

Gas

Content

Gas

Pressure

Cel 1 ul ar H/W

Thermal Conductivity X X X X Delta L/L X X X X Tensile Strength X X Tensile Modulus X X Compressive Strength X X Compressive Modulus X X

- 90 -
References ( IF)

Arvidson, J. M. , Bell, R. S. , Sparks, L. L. , and Guobang, C. (1983). Tensile,

Compressive, and Shear Properties of a 96 kg/m^ Polyurethane Foam at Low

Temperatures, NBSIR 83-1696, National Bureau of Standards, Boulder, CO.

Arvidson, J. M. and Sparks, L. L. (1981). Low Temperature Mechanical Properties

of a Polyurethane Foam, NBSIR 81-1654, National Bureau of Standards,

Boulder, CO.

Arvidson, J. M. , Sparks, L. L. , and Guobang, C. (1983). Tensile, Compressive,

and Shear Properties of a 64 kg/m^ polyurethane Foam at Low Temperatures

,

NBSIR 83-1684, National Bureau of Standards, Boulder, CO.

ASTM Annual Book of Standard s, American Society for Testing and Materials,

Philadelphia, PA.

Standard C177. Steady-State Thermal Transmission Properties by Means of

the Guarded Hot Plate, Part 18.

Barkley, R. M. (1983). Private communication . Dr. Barkley, Department of

Chemistry, University of Colorado, Boulder, CO.

DeGisi, S. L. and Neet , T. E, (1976). Predicting the Compressive Properties of

Rigid Urethane Foam, J. Appl . Polym. Sci. 20, pp. 2011-2028.

Du Pont (1979). Thermodynamic Properties of Freon 11 Refrigerant, Bulletin A-84529, E. I. Du Pont de Nemours Co., Wilmington, DE.

Exner, H. E. (1969). Discussion of the Relation Between Grain Section and Grain

Size, J. Inst. Metal s 97^, 191-192.

Gorring, R. L. and Churchill, S. W. (1961). Thermal Conductivity of Heterogeneous Materials, Chem. Eng. Prog. J57, 53-59.

Harding, R. H. (1960). Determination of Average Cell Volume in Foamed Products,

Mod. Plast. 37, 156-213.

- 91 -
Harding, R. H. (1964). Heat Transfer Through Low-Density Cellular Materials, I

and EC Process Design and Development _3 , 117-125.

Hensler, J. H. (1968). The Relation Between Grain Section and Grain Size,

J. Inst. Met. 96, 190-192.

Hi 1 yard, N. C. and Young, J. (1982). Introduction, in Mechanics of Cel lular

Plastics , N. C. Hilyard, ed., MacMillan Pub. Co., New York, 21.

Kirby, R. K. and Hahn, T. A. (1971). Fused-Silica Thermal Expansion, Standard

Reference Material 739, Office of Standard Reference Materials, National

Bureau of Standards, Washington, D.C.

Kirby, R. K. and Hahn, T. A. ( 1 9-7 5 ) . Copper Thermal Expansion, Standard Reference Material 736, Office of Standard Reference Materials, National Bureau

of Standards, Washington, D.C.

Menges, G. and Knipschild, F. (1982). Stiffness and Strength-Rigid Plastic

Foams, in Mechanics of Cellular Plastics , N. C. Hilyard, ed., MacMillan Pub.

Co. , New York, 27-72.

NASA (1975). High-Temperature Capacitive Strain Measurement System, NASA Tech.

Brief B75-10069.

Products Research Committee (1980). Materials Bank Compendium of Fire Property

Data, J. W. Lyons, Chairman, National Bureau of Standards, Washington, D.C.

Reed, R. P. , Arvidson, J. M. , and Durcholz, R. L. (1973). Tensile Properties of

Polyurethane and Polystyrene Foams from 76 to 300 K, in Advances in Cryo -

genic Engineering 18, K. D. Timmerhaus, ed.. Plenum Press, New York, NY,

184-193.

Rice, D. M. and Nunez, L. J. (1962). Average Cell Volume of Rigid Polyurethane

Foams by Means of an Air Comparison Pycnometer, SPE J. _18, 321-323.

- 92 -
Roberts, J. M. , Herring, R. B. , and Hartman, D. E. (3.958). The Use of Capacitance Gauge Sensors to Make Precision Mechanical Property Measurements, in

Materials Technology , American Society for Mechanical Engineers, New York,

87-96.

Schael , G. W. (1967). Characteri zation of the Structure of Cellular Plastics,

J. Appl . Poly. Sci. U , 2131-2142.

Skochdopole, R. E. (1961). The Thermal Conductivity of Foamed Plastics, Chem.

Eng. Prog. 57 , 55-59.

Smith, C. S. and Guttman, L. (1953). Measurement of Internal Boundaries in

Three-Dimensional Structures by Random Scattering, J. Met. 197 , 81-87.

Smith, D. R. , Hust, J. G. , and Van Poolen, L. J. (1981). A Guarded-Hot-Plate Apparatus for Measuring Effective Thermal Conductivity of Insulations Between

80 K and 360 K, National Bureau of Standrads (U.S.), NBSIR 81-1657.

Somers, E. V. and Cyphers, J. A. (1951). Analysis of Errors in Measuring Thermal

Conductivity of Insulating Materials, Rev. Sci. Instrum. 22, 583-586.

Sparks, L. L. (1979). Cryogenic Foam Insulations: Polyurethane and Polystyrene,

in Nonmetal lie Materials a nd Composites at Low Temperatures , Plenum Publishing Corporation, New York, NY.

Sparks, L. L. (1980). Low-Temperature Properties of Expanded Polyurethane and

Polystyrene, in ASTM STP 718, American Society for Testing and Materials,

Philadelphia, PA.

Sparks, L. L. (1981). Thermal Conductivity of a Polyurethane Foam from 95 K to

340 K, NBSIR 82-1664, National Bureau of Standards, Boulder, CO.

Thompson, A. W. (1972). Calculation of True Volume Grain Diameter, Metallography 5_, 366-369.

- 93 -
Touloukian, Y. S. , Liley, P. E. , and Saxena, S. C. (1970). In Thermal Conductivity: Nonmetal lie Liquids and Gases, Thermophysical Properties of Matter ,

Vol. 3, IFI/Plenum, New York, NY.

Tsederberg, N. V. (1965). Thermal Conductivity of Gases and Liquids , MIT Press,

Cambridge, MA, 144.

Tye, R. P. and Spinney, S. C. (1976). Thermal Conductivity of Concrete: Measurement Problems and Effect of Moisture, Bull. Int. Froid, Annexe 1976-2,

119-127.

- 94 -
INSULATING CONCRETES

Overall Project Objective (IC)

There are four immediate objectives for the insulating concrete effort:

(1) To collect information on commercially available insulating concretes.

(2) To evaluate existing data to determine applicability of test methods,

quality of data, and f itness-for-service of insulating concretes.

(3) To perform thermal and mechanical property screening tests on selected materials.

(4) To select one or more of the available materials for further testing.

The ultimate objective of the insulating concrete project is to supply the

LNG industry with the data base needed to incorporate one or more of the insulating concretes into plant design.

Project Description (IC)

A literature search designed to reveal information from past research on insulating concretes was done. This effort was initiated by a computerized search

in the following data bases: COMPENDEX, INSPEC, NTIS, and SSIE (further information in reference section under Data bases). The references cited in the computer identified papers were also selectively collected.

Screening tests performed at NBS to supplement the literature survey consisted of measuring the thermal conductivity of five candidate types and the

modulus of rupture and the compressive strength of four candidate types of concretes. The materials were supplied by three private companies and Brookhaven

National Laboratory (BNL).

In addition to the information collected from the literature and the screening tests, discussions with users and producers of insulating concretes were also

of value in evaluating these materials. The interest generated by this survey

for polymer based materials resulted largely from these discussions.

- 95 -
Project Rationale and Projected Benefits (IC)

Increased use of LNG and other liquid fuels along with more stringent safety

regulations, i.e.. Congressional Record 193.2059 (Federal Register, 1980) entitled Flammable Vapor-Gas Dispersion Protection, have created a need for an inexpensive, abundant material to be used in the construction of storage tank dikes

and basins. One or more of the insulating concretes could be developed to fill

the gap existing between the properties of good insulators, such as expanded

plastics, and natural materials, such as sand/soil/rock. The general attributes

needed for the dike/basin application include a reasonable degree of impermeability to water and liquid fuels, mechanical strength to support service vehicles, long unattended lifetime, ease of installation, material integrity when

subjected to thermal shock, a relatively low thermal conductivity, and a relatively low cost. Once developed, use of a material with these attributes will

almost certainly not be limited to dike construction.

Insulating concrete is common in the construction industry at the present

time and several commercially produced products are available. The primary applications are roof insulations, firewalls, and air conduits. The engineering

data developed for these purposes is not sufficient for design of cryogenic fuel

storage installations.

The benefits of developing and using such a material are enormous both from

the standpoint of safety and efficient land utilization. Insulated dike/basin

areas would allow new tanks to be sited in populated areas, i.e., near the users,

and in the event of a catastrophic tank failure and fire, would minimize both

loss of life and property damage.

- 96 -
TECHNICAL DISCUSSION (IC)

Work Plan (IC)

Three sources of information were available for assessing insulating concretes: open literature, industry files and experience, and new experimental

data. The literature search and discussions with industry were to be concurrent

and last from beginning to end of the effort. The experimental portion was designed to fill in gaps in information from the other sources. Three screening

tests, thermal conductivity, modulus of rupture, and compressive strength were

selected. The mechanical tests were to be done at 76 and 300 K. Based on all

information available at the end of the survey period, a recommendation was to be

made regarding materials and further reseach.

Work Performed and Results (IC)

The literature search resulted in 301 hard copies and microfiche. Of these,

approximately 30 contained data which could be used directly to evaluate and

select materials for use in dikes and impounding areas. The number of references

containing data for low temperatures is even more restricted. Annotated bibliographies have been prepared for nine of the technical papers: expanded shaleportland cement (Monfore and Lentz, 1962; Lentz and Monfore, 1965), vermicul i te-

,

perlite-, or polystyrene-portland cement (Adams, 1969; Reid and Wang, 1978; Reid,

1980), cel 1 ul ar-portl and cement (Richard, Dobogai, Gerbardt, and Young, 1975;

Richard, 1977), polymer matrix (Lang, Moorhouse, and Paul, 1980; McClune and

Moorhouse, 1981). These bibliographies follow the References (IC) section. The

remaining sources are given in the References (IC) section. The information contained in these papers is of a general interest nature. It was not possible to

group these diverse papers into meaningful sets so titles were included in the

references and can be used as guidelines to the paper's contents. Data from the

literature search are shown in figures 49 through 52.

- 97 -
THERMAL

CONDUCTIVITY,

W/(m-K>

100 125 150 175 200 225 250 275 300

TEMPERRTURE , K

Figure 49. Thermal conductivity as a function of temperature with moisture

content (Lentz and Monfore, 1965) and density (Adams, 1969) as parameters.

- 98-
SPLITTING

STRENGTH,

MPa

TEMPERATURE, K

Figure 50. Splitting strength as a function of temperature for an expanded shall?

concrete with density of 1554 kg/m^ (Monfore and Lentz, 1962)

- 99 -
30

29

28

27

26

25

24

23

22

21

20

Fi<

125 150 175 200 225 250 275 300

TEMPERATURE, K

51. Compressive Young's modulus as a function of temperature for an expanded shale concrete of density 1554 kg/m^ (Monfore and Lentz,

1962).

- 100 -
Figure 52. Compressive strength as a function of temperature for expanded

shale/portland (Monfore and Lentz, 1962) and for several lightweight

concretes at 295 K (McClune and Moorhouse, 1931).

- 101 -
Table 25 lists the companies and people contacted regarding lightweight concrete. Some entries represent a single phone contact, while others involved personal visits and extensive correspondence. Materials used in the experimental

phase were acquired from organi zations listed in this table. Discussions with

members of the GRI Advisory Group were useful in establishing the needs of industry as well as the general state of knowledge of insulating concretes.

Screening tests performed in support of the literature survey resulted in

data for thermal conductivity, compressive strength, and modulus of rupture.

These data are plotted in figures 53 through 55.

The thermal conductivity data, figure 53, were obtained in an insulating

vacuum environment. The values for portl and/polystyrene are lower than those

usually reported because of porosity and the concomitant lack of gas conduction.

The values for the less porous polyester-based materials are not expected to be

strongly affected by the vacuum environment. Adjusting the port land/ polystyrene

values to account for the lack of gas conduction would increase the conductivity

at 285 K to approximately 0.07 W/(m*K). The empirical relationship given later

in eq (13) yields a conductivity of 0.08 W/(m*K) for this mix.

Discussion of Results (1C)

Although the data base for insulating concretes is very limited, several

tentative conclusions can be drawn from the available information. Compressive

strength arjd thermal conductivity can be used to evaluate the relative merits of

the candidate materials.

In order to allow tank maintenance, light traffic must be allowed in the

tank basin. A minimum compressive strength of 5 MPa (725 psi) is estimated. The

screening tests at NBS (fig. 54) indicate that the particular specimen of

portl and-polystyrene (342-kg/m^ density) is not strong enough for this

- 102 -
Table 25. Industrial sources of information and/or materials used in the N5S/GRI

survey of insulating concretes. This list is not comprehensive in regard to companies involved with lightweight concretes and no endorsement, is implied.

Company Telephone Contact Person

BASF

Parsippany, NJ

(201) 263-3400 Bill Fairweather

British Columbia Hydroel ectric

Vancouver, BC

(604) 298-1311 Robert Booth and

Ken Griffiths

British Gas

Solihull, U.K.

44-21-705-7531 John Moorhouse

Brookhaven National Lab

Upton, NY

(516)282-2123 Meyer Steinberg,

Lawrence Kukacka,

and Toshi Sugama

Chicago Bridge a Iron

Plainfield, IL (815) 436-2912 Anthony Bellafiore

Concordia University

Montreal , Quebec

(514) 879-5995 Norman Low

Concrete Technology

Tacoma , WA

(206) 383-3545 Arthur Anderson

Global Marine

Newport Beach, CA

(714) 752-5050 Abraham Person

Institute of Gas Technology

Chicago, IL

(312) 567-3726 Phillip Anderson

Koppers

Pittsburgh, PA

(412) 227-2279 George St iffy

Lonestar

Los Angeles, CA

(213) 703-1267 M. Gunasekaran

Massachusetts Institute of

Technol ogy

Cambridge, MA

(617) 835-1000 Robert Reid

National Bureau of Standards

Gaithersburg, MD

(202) 921-2810 Geoff Frohnsdorf

Norton

Worcester, MA

(617) 853-1000 David Rostoker

Perlite Institute

New York, NY

(212) 265-2145 Robert Milanese

Portland Cement Association

Skokie, IL

(312) 966-6200 Paul Klieger,

David Whiting,

and Albert Litvin

Preload Technology

Garden City, NY

(516) 222-0550 Nicholas Legates

Respect a .America

Elk Grove, IL (312) 860-5999 Larry Farrel

1

San Diego Gas and Electric

San Diego, CA

(619) 232-4252 Barry Brunei le

Shell International

London, England

44-1-934-1234 Collin McClune

Sunderland PolytecnicSunderland, England

44-7-837-9316 A. L. Marshall

T. Y. Lin International

San Francisco, CA

(415) 982-1050 Harvey Haynes

Testing Engineers, San Diego

San Diego, CA

(619) 225-9641 Bill de Berry

United States Navy

Port Hueneme, CA

(805) 982-5923 Robert Rail

W. R. Grace

Denver, CO

(303) 722-5707 Gary Poindexter

- 103 -
THERMAL

CONDUCTIVITY,

W/(m-K)

Figure 53. Thermal conductivity of several insulating concretes as a function of

temperature. The testing environment was insulating vacuum.

- 104 -
COMPRESSIVE

STRENGTH,

MPo

is

TEMPERATURE, K

Figure 54. Average compressive strength of several insulating concretes as a function of temperature (determined at NBS).

- 105 -
TEMPERRTURE, K

Figure 55. Average modulus of rupture of several insulating concretes as a function of temperature (determined at NBS).

- 106 -
application and that one of the polyester-gl ass materials (554-kg/m3 density)

is marginal in this respect. For portl and-cement-based materials this criterion,

used in eq (15), establishes a minimum density of about 725 kg/m^. As seen in

figures 52 and 54, compressive strength increases or remains approximately

constant as temperature decreases. Ambient temperature data can therefore be

used as the worst case situation.

Compressive strength as a function of density (in k

j

»

)

at ambient

temperature can be estimated by

Compressive Strength = 4.132 x 10"^ x p + 4.469 x 10"^ x (15)

for portl and-cement-based materials. A similar, but much more tenuous relationship

Compressive Strength = 3.174 x 10"^ x p + 1.639 x 10" 5 x p^ (16)

can be used for polymeric-based materials. The least-squares fits in eqs (15)

and (16) were based on data given by McCl une and Moorhouse (1981) and the NBS

data given in this report. It must be stressed that these rel ationships are not

intended to be precise but rather to express trends for widely different

materials as functions of density.

Selection of material based on thermal properties is more complex. The

economics of the site area and material costs would necessarily cO'ie into play in

making this decision. The relative thermal property merits of the materials and

the estimate of the effect of water absorption can, however, be estimated.

The solution to the one-dimensional heat flow equation for infinite slabs

leads to the boil off rate for liquefied gas spills

1/2 1/2 1/2 1/2

M= (k P C) (aTA)/(H

v

tt t ) = (k P C) G (17)

where G represents a collection of terms not related to the slab material.

- 107 -
M is the LNG boil off rate, k is thermal conductivity, p is density, C is specific heat, aT is temperature difference between the LNG and substrate, A is

area, Hv is heat of vaporization of LNG, and t is time. The ambient temperature thermal conductivity for both Portland- and resin-based concretes can be estimated by

k = 0.1453 - 3. 1319 x

10“'" x p + 3.8844 x 10“ 7 x P 2

(18)

for dry materials. The boil -off rate can be expressed as a function of density

and specific heat.

-4 2 -7 3 If?

M = [(0. 1453p - 3.1219 x 10 x p + 3.8844 x 10 x p )C] G (19)

For purposes of comparison, specific heat of portl and -based materials is

840 J/kg*K (Yoshiwa and Iwata, 1977) while that for resin-based materials is

• • 1000 J/kg*K (Sparks, 1983). For a given density, M (polymer base) = 1.1 M

(Portland base). Due to uncertainties in the values of thermal conductivity and

specific heat for nonspecific materials, this 10% difference should be considered

semi -quanti tati ve.

Absorption of water is of major importance in selecting the dike/basin material. Lang, Moorhouse, and Paul (1980) and McClune and Moorhouse (1931) have

studied the rate of water uptake in various materials as well as alternative

methods of reducing this phenomenon. Their work is summarized in the annotated

bibliography section.

Concern about water uptake is due to the dependence of boil -off rate on p,

k, and C (eg 17); each of these parameters increase as water content increases.

The relationship for thermal conductivity as a function of density (eq 18) applies to dry materials. Valore (1956) has shown empirically that the thermal

conductivity for a given specimen will increase by 5% for each 1% increase in

- 108 -
density due to absorption of free water. Specific heat is also increased due to

the relatively high heat capacity of water. The net effect of water absorption

can be seen by comparison of LNG boil -off for a given material before and after

water absorption. Properties of the material in the oven-dry condition are p

= 1586 kg/m3, k = 0.62 W/nrK, and C = 840 J/kg*K. The resulting LNG boiloff is M = 909 G. After 10 volume percent (6.3% by weight) water absorption, k

= 0.82 W/nrK, p = 1686 kg/m^, and, by the rule of mixtures, C = 1051 J/kg*K

• • • Boil -off for the damp material is M = 1205 G. M(damp)/M(dry) = 1.33, or an increase in LNG boil -off of 33%. An increase of this magnitude significantly

alters the distance down wind from the tank at which a 5% methane concentration

occurs (Arthur D. Little, 1974). McCl une and Moorhouse (1981) find absorption in

the range 10 to 30 volume percent for untreated portland-based materials so that

the effect computed above is approaching a minimum that must be expected.

The ratio of compressive strength to thermal conductivity, Q, can be used as

an indicator of the relative fitness of materials for use in dike/basin areas.

It does not, however, take several very important factors into account, e.g.,

initial cost, maintenance, flanmabil ity, and water absorption. This ratio is

given in table 26 for the lightweight concretes tested at NBS and for several

materials reported in the literature. Ordinary concretes, which are stronger but

have higher conductivity, have Q values on the order of 20. The resin-based

materials listed in the table are suggested by this ratio while the Portland/

polystyrene materials appear to be least usable. Portland/expanded shale is the

most dense material considered. The Q for this material approaches that of the

resin-based mixes.

- 109 -
Table 26. Density, thermal conductivity (k), compressive strength (CS), and the ratio Q

= CS/k for the lightweight concretes tested at NBS and for several materials

reported in the literature. The data are for 295 K.

Material Source

Density

(kg-iTT 3

)

k (W*nrl* K"1

)

CS

(MPa)

Q

(MPa-m-K-ir 1

)

polyester/perl ite/BNL NBS 896 0.15 22 143

polyester/glass/BNL NBS 779 0.09 10.5 114

polyester/gl ass/Rostoker NBS 554 0.07 6 81

portl and/polystyrene NBS 342 0.07 2 28

epoxy/resi n/concrete A 1100 0.3 42 140

polyester/fine clay A 1425 0.4 37 92

portl and/polystyrene A 445 0.1 1 10

portland/expanded shale B 1554 0.8 41 51

A: McClune and Moorhouse (1981).

B: Lentz and Monfore (1965); Monfore and Lentz (1962).

- 110 -
Major Achievements (IC)

The results of the literature survey and the discussions within the userproducer communities emphasized the undeveloped state of the candidate materials

for cryogenic applications. Interactions based on the information available has

helped to redirect industrial efforts to develop usable material (s). Polymerbased materials are now being evaluated more thoroughly in this country.

Major Technical Problems (IC)

The over-riding problems encountered were the lack of low temperature data

in the literature and user inexperience with the candidate materials. This

placed an unexpected burden on the experimental screening effort. The term and

funding of the survey were not sufficient to obtain and perform necessary tests

on the variety of materials and the range of densities needed to establish quantitative selection criteria.

Conclusions (IC)

The thermophysical properties recommend resin-based materials for use in

dike/basin applications. The choice of these materials over lightweight

portl and-cement-based materials is due to high strength-to-wei ght ratio and low

thermal conductivity. Low absorption allows thermal conductivity to remain fixed

after exposure to water. There are, however, unanswered questions which must be

addressed before these materials can be used in the proposed applications.

Resins are organic in nature and are therefore relatively flammable. The effectiveness of fire retarding additives in preventing resin combustion must be

thoroughly evaluated before installation around a LNG tank. Resin-based materials are inherently more expensive, at least initially, than portl and-based materials. This fact will lead to use of resin-based materials as caps on less

- 111 -
costly substrates. The quality of bond between cap and substrate and the effect

of environmental extremes on this bond must also be evaluated.

Strength-to-wei ght ratios for portl and-cement-based materials are lower than

those for the resin-based materials. Relatively dense mixes are required to meet

the strength requirements and the thermal conductivity is a function of density.

Water absorption in these materials also causes thermal conductivity to increase.

It has been shown that reasonably low equilibrium levels of free water can be

maintained by particular mix treatments. In view of this and the possibility of

further alleviation of absorption problems by drainage design, these materials

should not be disregarded. Experience in placing the more conventional materials

as well as initial costs are definitely in favor of portl and-based materials.

Recommendations (IC)

Several unanswered questions relating to resin- and portland-based materials

were mentioned in the Conclusions (IC) section above. The following research is

needed to provide the necessary answers:

(1) Concentrated study of the tensile stress-strain relationship, tensile

and compressive strengths, thermal expansion, and thermal conductivity

of one type of resin with one type of lightweight aggregate. A range

of densities of this material would be required. Without this information, thermal stresses expected from an LNG spill could cause fractures

and lead to an unacceptable LNG boil -off rate. These data should cover

the temperature range from 100 K to ambient. The properties mentioned

must be determined on specimens which are large compared to aggregate

dimensions.

(2) Tests involving large slabs of the selected material (same resin and

aggregate type as selected for study in (1) above) should be done to

- 112 -
compliment the property determinations discussed in project (1). Placing, large scale batching, and batch-to-batch uniformity would be determined. Specimens for the study in (1) would ideally come from these

mixes. Aging in outdoor environments and effects of thermal shock

would be assessed.

(3) Programs similar to (1) and (2) are needed for a portl and-cement-based

material with one type of aggregate. In addition to the previously

mentioned parameters, effectiveness of techniques to prevent water absorption should be examined. Quantitative rates and equilibrium levels

of moisture would be determined.

(4) Flammability tests are needed for the particular resin chosen. Types

of gases evolved during combustion should be determined.

(5) The economics involved in choosing either type of material or combinations thereof should be studied as functions of site particulars.

Relative costs of capping, substrate type, maintenance, and drainage

facilities are needed and must be expressed in a form which can be related to widely variable site particulars.

A single, best material for use in insulating dikes and impounding areas

cannot be selected based on available information. Our assessment indicates that

there are six types of materials which would be useful in particular circumstances: tl) expanded shal e/portl and , (2) perl ite/portl and , (3) polymer/perlite,

vermiculite, expanded shale or expanded clay, (4) polymer/glass , (5) Portland/

polystyrene, and (6) vermicul ite/portl and. Although data is not available to establish a figure of merit for all of these materials, (1), (3), and (4) appear to

be the best alternatives.

- 113 -
References (IC )

Aagaard, V. and Ladegaard, B. H. Liquefied Natural Gas Storage, Barcelona, Preload Bulletin T-39.

Adams, Ludwig (1965). Thermal Conductivity of Perlite at Low Temperature, Cryogenic Tech. , 117-118.

Adams, Ludwig (1969). Thermal Conductivity of Perlite Concrete, Cryogenic

Tech. 5, 10-11.

Alleaume, J. I. (1970). Fixed Fluid-Tight Tank or the Like and Method of Constructing Same, U.S. Patent Office, Vol . 3511003.

Altman, Von Klaus (1974). The Behaviour of Moisture in Foam- Polystyrene Concrete

and Methods of Testing, Material prufung 1_6, 3-6.

American Concrete Institute Detroit, MI:

Building Code Requirements for Reinforced Concrete (1963). ACI Standard

318-63.

Design and Construction of Circular Prestressed Concrete Structures (1970).

Report by Committee 344.

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Rostasy, F. S. and Wiedemann, G. (1980). Stress-Strain-Behavior of Concrete at

Extremely Low Temperatures, Cem. Concr. Res. 1£, 565-572.

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Cement Mortars Due to Temperature, Cem. Concr. Res. 10^, 157-164.

Rostasy, F. S., Schneider, U., and Wiedemann, G. (1979). Behavior of Mortar and

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- 129 -
Short, A. and Kinniburch, W. (1963). Lightweight Concrete, C. R. Books Limited,

John Wiley a Sons, Inc.

Slobodanik, I. Y. (1968). Expanded Perlite Fines, The Concrete Society, First

International Congress on Lightweight Concrete 2 ,

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320 K, NBSIR 81-1651, National Bureau of Standards, Boulder, CO.

Sparks, L. L. (1983). Specific Heat in Materials at Low Temperatures , in

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Society for Metals, Metals Park, OH, 69.

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Staff, Oil and Gas Journal (1976). Concrete Due Test as Barrier in Marine LNG

Service, Oil Gas J. 74, 64-6.

Staff, Pipeline and Gas Journal (1982). Scorecard, Pipeline Gas J. 80, 32-42.

Staff, Plastics-Rubbers-Textiles (1970). Void Forming in Concrete with Expanded

Polystyrene, PI astics-Rubbers-Textiles _1, 331-332.

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19-21.

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- 130 -
Steinberg, M., Kukacka, L. E., Colombo, P., Auskern, A., Manowitz, B., Dikeou,

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Cylinders, Thesis, University of Wyoming, Civil and Archi tectural Engineering, Laramie, WY.

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BNL 51390, Brookhaven National Laboratory, Upton, NY.

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and the Hexagonal Ices, Physics of Ice , Plenum Press, New York, NY.

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- 131 -
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from +20°C to -196°C, Supplementary Paper III -24, Cement Association of

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- 132 -
Weigler, H. and Sieghart, K. (1980). Structural Lightweight Aggregate Concrete

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Weigler, H. and Micolay, J. (1973). Temperaturdehn-und Warmel ei tzahl en von

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Yasin, Y. D. (1972). Comparative Evaluation of Methods Used for Determining the

Cryogenic Phase Transformations of Moisture in Construction Materials,

J. Eng. Phys. (USSR) 23, 907-908.

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Based on the Curve-Fitting Method for Measuring Thermal Properties at Cryogenic Temperatures, Cryoaenics 17., 273-282.

Ziembicka, H. (1977). Effect of Micropore Structure on Cellular Concrete Shrink

age, Cem. Concr. Res. 7, 323-332.

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ANNOTATED BIBLIOGRAPHIES (IC)

Expanded shal e/portl and

Monfore, G. E. and Lentz, A. E. (1962). Physical Properties of Concrete at Very Low Temperatures, J. PCA £, 33-39.

Na rra ti ve : The properties of various concretes were reported by the authors in

the period 1962 through 1966. This work is referred to in a large percentage of

papers dealing with concrete at low temperatures. The purpose of their study was

to develop a data base to use in the design of LNG facilities. The temperature

range studied was -157 to 24 °C. The materials of primary interest were ordinary

weight concretes, e.g., densities on the order of 2290 kg/m^ (143 lb/ft^).

One series of expanded-shal e-portland specimens were included; the density of

these specimens was 1554 kg/nr (97 ib/ft^) which puts them in the structural

lightweight category.

Material : Expanded shal e/portl and; 1554 kg/m^ (97 Ib/ft^) density;

334.6 kg/m3 (6.0 bag/yd^) cement content; 0.45 t/kg (5.1 gal/bag) water to

cement ratio.

Data : Young's modulus (moist condition); -157 T _< 24 °C.

Thermal contraction (moist condition); -157 <. T _< 24 °C.

Compressive strength (moist condition); -157 _< T 24 °C.

Splitting strength (moist condition); -157 <_ T _< 24 °C.

Concl usions . Compressive strength, compressive modulus, and splitting strength

show essentially no temperature dependence on temperatures above 0 °C. Below

this temperature, each increases rapidly with decreasing temperature. Splitting

strength exhibits a maximum at -58 °C while the compressive strength and modulus

continue to increase monotonical ly as temperature decreases. These trends were

also observed for a moist concrete mortar by Arvidson, Sparks, and Steketee

(1982). Thermal contraction also exhibits an inflection at about -58 °C. This

behavior has been observed for other types of concrete (Tognon, 1968; Goto and

Miura, 1978).

- 134-
Expanded shal e/portl and

Lentz, A. E. and Monfore, G. E. (1965). Thermal Conductivity of Concrete at Very Low Temperatures , J. PCA _7, 39-46.

Narrati ve : This paper is the second of the series by Lentz and Monfore dealing

with concretes at low temperatures. One of the materials discussed is expanded

shale/portland in moist, 50% relative humidity (RH), and oven-dry conditions.

The density of this material is 1586 kg/m^ which falls in the structural lightweight category. These data, along with those reported in Monfore and Lentz

(1962), constitute a complete set of low-temperature properties for a particular

formulation and are unique in this regard.

Material : Expanded shale/portland; 1586 kg/m^ (99 lb/ft^) density; 334.6 kg/m^

(6.0 bag/yd^) cement content; 0.45 A/kg (5.1 gal/bag) water to cement ratio.

Data : Thermal conductivity (moist, 50% RH, oven dry); -157 <. T _< 24 °C.

Concl usions : These data emphasize the importance of moisture content on the con- ductivity of concrete. The general rule of a 5% change in conductivity for each

1% change in density due to free-moi sture content is closely followed at -160 °C.

The separation of data points for these data would preclude identifying possible

inflections in the -70 to -20 °C temperature range. The possibility exists for

significantly higher conductivities in this range for moist concretes. Rapid

changes in splitting strength and thermal contraction were observed by Monfore

and Lentz (1962) and in thermal conductivity by Sparks (1981).

- 135 -
Vermiculite, polystyrene/portl and cement, soils, corrugated aluminum

Reid, R. C. and Wang, R. (1978). The Boiling Rates of LNG on Typical

Dike Floor Materials, Cryogenics _18, 401-404.

Reid, R. C. (1980). Boiling of LNG on Typical Dike Floor Materials,

Final Report to Gas Research Institute, GR 1-79/0026

.

Narrati ve : Spill tests were conducted to determine the boiling parameters of

several candidate dike insulating materials. The boiling rate, M/A, was found to

be M/A = Ft" anc) p = (k?rC/p

) - 1/2 aT/aH. Both coated and uncoated specimens were tested and no difference in boiling rates was detected. Apparent thermal

conductivities were computed.

Material : Polystyrene-portland , vermicul ite-portl and , soil, corrugated aluminum,

polyurethane.

Data : Boiling rate, thermal conductivity.

Cone! usions : The relative boil -off rates for the insulating concretes were roughly proportional to density. The boiling parameter, F, for these materials

is about a factor of two higher than that of the 120 kg/m^ polyurethane foam

tested, and about a factor of eight lower than the compacted soil tested. The

problem of moisture uptake was not addressed. The authors found that corrugated

aluminum over a sand substrate served to limit the boiling rates to about the

level of the insulating concretes.

- 136 -
Cellular Portland cement concrete

Richard, T. G. (1977). Low Temperature Behavior of Cellular Concrete,

J. Am. Concr. Inst. _71> 173-178.

Richard, T. G. , Dobogai , J. A., Gerhardt, T. D., and Young, W. C. (1975). Cellular Concrete--A Potential Load-Bearing Insulation for

Cryogenic Applications, IEEE Trans, on Magn. MAG-11 , 500-503.

Narrati ve : The material studied is a neat-cellular concrete consisting of type I Portland cement, water, and a hydrolized waste-protein-foaming agent. Several

densities were prepared and properties were studied as a function of density at

23 and -196 °C.

Material : Cel 1 ul ar-portl and-cement concrete.

Data : Specific strength as a function of water to cement ratio; ultimate com- pressive strength, elastic modulus, secant modulus, and thermal conductivity as functions of density.

Concl usions : The data are indicative of moist specimens which tend to make the

thermal conductivity data relatively high. No indication of water uptake is

given but would probably be high, at least comparable to vermiculite- and

polystyrene-portl and. The ratio compressive strength/thermal conductivity for a 1200 kg/m^ specimen indicates that this type of material compares reasonably

well with other non-resin based concretes.

- 137 -
Perl ite-portl and cement concrete

Adams, L. (1969). Thermal Conductivity of Perlite Concrete, Cryogenic

Tech. 5, 10-11.

Narrative : This work presents an analytical study of thermal conductivity as a function of temperature with density and free-water content as parameters.

Material : Perl ite-portl and-cement concrete.

Data : Analytical values of thermal conductivity in the temperature range 144 to

255 K, free moisture content from 0 to 60%, and oven-dry densities from 352 to

577 kg/m^ 0

Concl usions : The values presented in this paper are useful because the ana- lytical relationship is based on reasonable observations of the behavior of other

materials and there are no experimental data for perlite concrete.

- 138 -
Polymer matrix composites and waterproofing

Lang, R. Z. J., Moorhouse, J., and Paul, G. J. (1980). Waterproof

Insulation Materials, British Gas Corporation MRS E 372, Institute

of Chemical Engineers Seventh Symposium on Process Hazards.

Narrati ve : This paper reports the continuation of the effort to establish a viable insulating material for dike-impounding systems of LNG-storage facilities

(McClune and Moorhouse, 1981). Water uptake in outdoor exposures is reported for

several treated and untreated lightweight concretes. Mass rate of boil -off of

LNG is experimentally determined and used to compare the various types of speci- mens mentioned above with varying water contents. Results from tests to evaluate

the bond strength of resin based materials to ordinary concretes are reported.

Material : Ordinary (sand and gravel aggregate) concrete, lightweight concrete,

and resin concrete.

Data : Comparison of water uptake of treated and untreated lightweight concrete;

LNG boil -off rates as a function of water content and as a function of time from

spill; tensile bond strength of lightweight-ordinary concretes.

Conclusions : As was shown in a previous publication, resin-based concretes are superior to treated lightweight concretes with regard to water uptake and com- pressive strength. Data presented here for the bond strength between resin and

ordinary concretes indicate that this should not be a major problem in the practical application of resin concretes. In applications where the exposure to

water can be reasonably limited, such as well graded or vertical sections, the

water uptake in treated lightweight concretes can be kept to levels causing relatively small increases in thermal conductivity, e.g., water content increasing

from 0 to 10% by volume increases the conductivity by approximately 50%.

- 139 -
Polymer matrix composites and water uptake

McClune, C. R. and Moorhouse, J. (1981). The Development of

Waterproof Insulating Materials Based on Lightweight Concrete,

Mag. Concr. Res. ^3, 27-36.

Narrati ve : This paper considers three areas of primary interest in selecting a material for use in the dike-impounding system of LNG-storage facilities. Several methods of reducing water uptake are discussed. The most effective of these

is to replace the cement binder with a resin binder. Addition of latex to the

Portland cement and/or to the aggregates used is also effective. The usual relationship between the compressive strength and density was not significantly affected by the waterproofing in the case of the portl and-based concretes. The

resin-based materials did not follow this relationship in that their compressive

strength was substantially higher than that for a portl and-based concrete of com- parable density. Thermal conductivity of both resin- and portl and-based materials exhibit similar density dependence at 30 °C.

Material

s

: Aerated, polystyrene, vermiculite and expanded-cl ay aggregates in

portl and-cement binder. Epoxy and polyester binders used with several unspecified aggregates and with clay aggregates. Latex, epoxy, and silicon admixtures.

Data : Water uptake and water content as a function of time in wetting and drying

environments. Compressive strength and thermal conductivity as functions of density.

Concl usions : Thermal conductivity of concretes increases roughly 5% for each 1%

increase in density due to free water content. This trend makes water uptake

critical to the performance of these materials. Waterproofi ng by application of

surface sealers is not satisfactory because thin layers of sealer are not effective and thick layers are expensive and are detrimental to the thermal properties. Reactive admixtures are not effective when used with lightweight con- cretes. Nonreactive admixtures, particularly latex, and treatment of aggregate

with waterproofi ng agents prior to mixing was found to be effective in reducing

water uptake. Resin-based concretes were most effective in reducing water uptake. Possible drawbacks to the use of resin binders are flammability, cost, and

bondability to substrate materials.

GPO 844 - 038

- 140 -
U »• OCPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date

ilBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NBSIR 84-3011 OR I -84/0086 April 1984

4 . TITLE AND SUBTITLE . —

hemal and Mechanical Properties of Polyurethane Foams and a Survey of Insulating

Concretes at Cryogenic Temperatures

5. AUTHOR(S)

L. L. Sparks and J. M. Arvidson

b . PERF ORMING ORGANIZATION (If joint or other than N BS. see in struction s) 7. Contract/Grant No. national bureau of standards 5081-352-0425

DEPARTMENT OF COMMERCE 8 . Type of Report & Period Covered

WASHINGTON. D.C. 20234 Final , Jan 1979-Feb 1981

9. r’ ) N SO RING ORGANIZATION NAME and COMPLETE ADDRESS (Street. City. State. ZIP)

Gas Research Institute

8600 West Bryn Mawr Avenue

Chicago, IL 60631

10 . supplementary notes

Document describes a computer program; SF-185, FlPS Software Summary, is attached. \BSTRACT A 200-word or less factual summary of most significant information. If document includes a significant

i bl lography or literature survey, mention it here)

Thermal and mechanical properties of expanded plastics, foams, are reported. The

system studied was rigid, closed cell, CCJI 3

F blown, polyether based pol yurethane. The

primary temperature range of study was 100 to 300 K; however, several properties were

determined to 4 K. The nominal densities of the foams tested were 32, 64, and 96 kg/mJ

. Properties reported are thermal conductivity, thermal expansion, strength and moduli in

tension and in compression, proportional limit, yield strength, ultimate strength, and

shear strength. Physical properties were determined both parallel and perpendicular to

the orthogonal axes of the bulk supplies. The gas content of the specimens was determined using a gas chromatograph-mass spectrometer and with a gas displacement pycnometer. Empirical procedures for estimating the temperature dependent thermophysical

properties were developed. These procedures are based on the experimental data and utilize the characteri zati on parameters for molar gas concentration, gas pressure, and cell

morphol ogy.

Regulations affecting vapor dispersion in the area around liquefied natural gas facilities make it attractive to construct dikes and impounding areas out of materials

having low thermal conductivities. Several insulating concretes have the general properties required for such applications. Screening tests were done to determine the

thermal conductivity, modulus of rupture, and the compressive strength of several polyester based materials with glass bead or perlite aggregate and of port land cement based

materials with vermiculite or polystyrene aggregate. A bibliography resulting from an extensive literature survey of lightweight concretes is presented. Seven of the references which were particularly applicable are presented in annotated form.

12. KEY WpRDS(S/x to twelve entries: alphabetical-order; capi ta I i ze.on ly prosper names- and separate <ey woreIs tv i cojODii i celT size; compressive strength; elongation; TTexuraT strehgtn; foam; glass bead; instil

low temperature; mechanical properties; modulus of rupture; perlite; polyester; polymer

concrete; polystyrene; portland cement; proportional limit; shear strength; tensi ] e str

th ^

‘^lA ^gp^cti^H

-ty ; th e rmal, expansion; vcrmicul i

-te ; yield strength;—fowqd *

1

ation

angth

v

| ~xj Unl imlted For Official Distribution. Do Not Release to NTIS

,

! Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

J Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Price

$16.00