Thermal Processing and Composite Laminate Formation 

of Ionic Block Copolymers for Protective Clothing 

by James Harris, Yossef A. Elabd, Eugene Napadensky,

and Paul Moy 

ARL-TR-2892 December 2002 

Approved for public release; distribution is unlimited. 
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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-2892 December 2002 

Thermal Processing and Composite Laminate Formation of 

Ionic Block Copolymers for Protective Clothing 

James Harris, Eugene Napadensky, and Paul Moy 

Weapons and Materials Research Directorate, ARL 

Yossef A. Elabd 

National Research Council Postdoctoral Associate

Approved for public release; distribution is unlimited. 
i

Acknowledgments 

This work was performed while Y. A. Elabd held a National Research Council Research 

Associateship Award at the U.S. Army Research Laboratory. The authors would like to 

gratefully acknowledge the assistance of Daniel Deschepper with the digital photographs in this 

technical report. 
ii

Contents 

Acknowledgments i

List of Figures iii

List of Tables iii

1. Introduction 1

2. Experimental 1

2.1 Materials..........................................................................................................................1 

2.2 Equipment .......................................................................................................................1 

2.3 Polymer Preparation........................................................................................................2 

2.3.1 Cryogenic Grinding...............................................................................................2 

2.3.2 Heat Press Preparation...........................................................................................2 

2.4 Thermal Pressing Procedure............................................................................................3 

2.5 Laminating Procedure .....................................................................................................4 

3. Results and Discussion 4

3.1 Pressed Polymer Film......................................................................................................4

3.2 Laminated Polymer/Fabric Composite............................................................................4 

3.3 Infrared Analysis .............................................................................................................4 

4. Conclusion 7

5. References 8

Appendix A. Programmable Steps 9

Appendix B. Further Instructions 10

Report Documentation Page 11 
iii

List of Figures 

Figure 1. Cryogenically ground polymer powder...........................................................................2 

Figure 2. Heat press assembly: (a) caul plate, (b) Teflon sheet, (c) Teflon sheet, (d) 40 Shore 

A (tan) 1/16 in, (e) 50 Shore A (black) 1/16 in, (f) 55 Shore A (black) 1/4 in, and (g) caul 

plate............................................................................................................................................3 

Figure 3. Pressed polymer film.......................................................................................................5 

Figure 4. Pressed polymer films of (a) low and (b) high ion content. ............................................5 

Figure 5. Poorly processed polymer film (powder pressed without using rubber sheets in 

heat press). .................................................................................................................................6 

Figure 6. Polymer/fabric composite, (a) top and (b) bottom views................................................6 

Figure 7. Polymer/fabric composite (side view).............................................................................7 

Figure 8. Infrared spectrum of solvent-cast (solid line) and pressed (dashed line) films...............7 

List of Tables 

Table A-1. Program 1. ....................................................................................................................9 

Table A-2. Program 2. ....................................................................................................................9 

Table A-3. Program 3. ....................................................................................................................9 
1

1. Introduction 

The development of “breathable” protective clothing is a main goal in outfitting the future U.S. 

Army soldier. Currently, butyl rubber is one of the standard materials used for chemical 

protective clothing (CPC). Butyl rubber provides a sufficient barrier to chemical agents, but it is 

also a barrier to water vapor, which results in unbearable levels of heat stress on the soldier [1]. 

Future materials design should focus on the development of highly selective CPC (i.e., an 

excellent chemical agent barrier, but also breathable and comfortable). Additionally, future CPC 

materials need to be lightweight, flexible, and durable to withstand battlefield conditions. 

Incorporating all of these properties into one material is a great technical challenge. 

Recently, investigators at the U.S. Army Research Laboratory (ARL) have developed a new 

material, an ionic block copolymer—highly sulfonated poly(styrene-isobutylene-styrene) 

(S-SIBS)—that possesses many of the desired properties for CPC [2]. S-SIBS contains two 

components: a flexible elastic barrier component and a hydrophilic breathable component. This 

new material is designed at a molecular level and self-assembles into unique structures on a nano 

level. Combining these different properties together into distinct nanostructures provides an 

excellent selective barrier for this application. 

In order to incorporate S-SIBS into a future garment, research will be required in a number of 

areas, particularly polymer processing. This study demonstrates a first attempt in processing 

S-SIBS into thin films (without the use of toxic solvents) and laminating it into a polymer/fabric 

composite for use as CPC. 

2. Experimental 

2.1 Materials 

Synthesis of S-SIBS was conducted at ARL, and the details of this procedure are documented 

elsewhere [2]. A standard battle dress uniform (BDU) fabric (50%/50% cotton/nylon), provided 

by the Natick Soldier Center (NSC), was used to produce polymer/fabric composites. Shore A 

40, 50, and 55 firmness rubber sheets, Teflon∗

 fluoropolymer sheets, and 0.64-cm (1/4-in) thick 

aluminum plates were used in the thermal processing procedure. 

2.2 Equipment 

A liquid nitrogen-cooled freezer mill (Spex CertiPrep 6750-115) was used to cryogenically grind 

the polymer. For thermal processing, a computer-controlled heat press (Tetrahedron Inc. MTP-

 ∗

 Teflon is a registered trademark of E.I. du Pont de Nemours and Company. 
2

24) was used. Infrared spectra of all polymer samples were collected using a Nicolet Nexus 870 

Spectrometer equipped with a diamond ATR objective (Spectra-Tech Infinity Series). The 

diamond ATR objective (refractive index = 2.73) is a nondestructive technique that provides 

intimate contact with the polymer sample. Infrared spectra were collected using 500 scans and a 

4 cm-1 resolution. 

2.3 Polymer Preparation 

2.3.1 Cryogenic Grinding 

Two grams of S-SIBS were cut into small (5 H 5 mm) pieces and placed into the steel-grinding 

cartridge of the freezer mill. The mill was cooled with liquid nitrogen for 25 min before 

grinding. The polymer was then ground in 6 cycles of 4 min each with 4-min rest intervals 

(power setting = 10). The ground powder was then placed in a specimen jar to keep out 

moisture. The powder was dried in a vacuum oven at 40 °C for 2 hr and then placed in a 

desiccant container overnight to limit moisture uptake. Figure 1 shows an example of the 

polymer powder produced using this procedure. 

Figure 1. Cryogenically ground polymer powder. 

2.3.2 Heat Press Preparation 

To prepare the heat press for thermal processing, aluminum caul plates, with dimensions of 

30.48 H 30.48 H 0.64 cm (12 H 12 H 1/4 in), were used with at least one face machined and 

polished to a 0.0032-μm (0.125-μin) finish. The polymer powder was sandwiched between the 

caul plates, rubber, and Teflon sheets. As shown in Figure 2, the order of rubber and Teflon 

layers was from softest to hardest. The first caul plate was covered with a Teflon sheet, 0.16 cm
3

E

G

F

D

C

A

B

e

g

f

d

c

a

b

Figure 2. Heat press assembly: (a) caul plate, (b) Teflon sheet, (c) Teflon sheet, (d) 40 Shore A 

(tan) 1/16 in, (e) 50 Shore A (black) 1/16 in, (f) 55 Shore A (black) 1/4 in, and 

(g) caul plate. 

(1/16 in) thick, followed by the polymer powder and a second Teflon sheet. Three layers of 

rubber sheets were used. The first (Shore A 40) and second (Shore A 50) rubber sheet were 

30.48 H 30.48 H 0.16 cm (12 H 12 H 1/16 in) in size. The third rubber layer was 0.64 cm (1/4 in) 

thick and was slightly larger than the desired final dimensions of the polymer film (i.e., 15.24 H

15.24 cm or 6 H 6 in). 

The polymer powder was processed using several programmable steps identified as programs 1–

3 (Appendix A, Tables A-1 through A-3). The configuration shown in Figure 2 was used for 

program 1 only. A second set of caul plates, coated with Frekote∗

 for a release film, was used for 

programs 2 and 3. 

2.4 Thermal Pressing Procedure 

A specified amount of S-SIBS powder was distributed over the Teflon sheet with a razor blade to 

a dimension slightly larger than the desired dimension of the polymer film. Experimentation 

revealed that 1 g of polymer powder can cover ~38.71 cm2

 (6 in2). The second Teflon sheet and 

layers of rubber were placed on top of the polymer powder, and program 1 (Appendix A, Table 

A-1) was used to convert most of the polymer powder to a film with an initial melt process. To 

 ∗

 Frekote is a registered trademark of Loctite Corporation. 
4

convert the remaining powder to a film form, program 2 (Appendix A, Table A-2) was used to 

produce the final product (freestanding film) by an increase of pressure at the same temperature. 

2.5 Laminating Procedure 

Program 3 (Appendix A, Table A-3) was used to laminate processed polymer films onto the 

BDU fabric, where both fabric and film were pressed together between two caul plates and a 

Teflon sheet. Further instructions are listed in Appendix B. 

3. Results and Discussion 

3.1 Pressed Polymer Film 

Figure 3 shows a freestanding film created using programs 1 and 2. Initially, films produced 

with program 1 were not uniform in thickness and contained areas that were not completely 

converted from powder to film. The increase in pressure in program 2 produces complete films 

with uniform thicknesses ranging from 254 to 300 μm (10–13 mils) from film to film. The films 

produced weighed ~327.9 g/m2 (9.7 oz/yd2) in accordance with American Society for Testing 

and Materials (ASTM) standard D3776-96 [3]. The films were translucent, containing a 

brownish tint. The color is related to the amount of ionic groups (sulfonic acid) in the polymer. 

Higher ion contents usually correspond to darker shades of brown (shown in Figure 4). Pressing 

the polymer powder without the use of rubber sheets when using program 1 produces a poor film 

(e.g., Figure 5). The Teflon/rubber layers act as an insulator from the heated caul plates and 

allows convection heating over conductive. This process results in a more uniform film 

thickness. Different rubber layers provide an evenly distributed load transfer from the caul 

plates to the polymer powder during heating and pressure. 

3.2 Laminated Polymer/Fabric Composite 

Figures 6 and 7 show a laminated polymer/fabric composite (top/outer, bottom/inner, and side 

view) produced using program 3. The BDU fabric used here was ~356 μm (14 mils) and 

weighed 168.2 g/m2

 (5.0 oz/yd2) in accordance with ASTM D3776-96. This makes the total 

weight of the polymer/fabric composite ~500 g/m2

, which increases the weight of the BDU 

fabric threefold. 

3.3 Infrared Analysis 

The infrared spectra of both solvent-cast and pressed films were examined to determine if any 

chemical changes occurred in the polymer due to heat pressing (shown in Figure 8). The four 

peaks, 1155, 1125, 1034, and 1007 cm!1

, are all infrared stretching vibrations associated with the 

ionic functional group in S-SIBS. Figure 8 shows that there is a negligible difference between 

the two spectra confirming that there is no chemical change in the polymer due to heat pressing 

the polymer.
5

Figure 3. Pressed polymer film. 

(a) Low ion content, light brown 

(b) High ion content, dark brown 

Figure 4. Pressed polymer films of (a) low 

and (b) high ion content.
6

Figure 5. Poorly processed polymer film (powder pressed without using 

rubber sheets in heat press). 

(a) Top/outer view 

(b) Bottom/inner view 

Figure 6. Polymer/fabric composite, (a) 

top and (b) bottom views.
7

Figure 7. Polymer/fabric composite (side view). 

-0.1

0

0.1

0.2

0.3

0.4

1500 1400 1300 1200 1100 1000 900 800

Absorbance

Wavenumber (cm-1)

1155 cm-1

1125 cm-1

1034 cm-1

1007 cm-1

Figure 8. Infrared spectrum of solvent-cast (solid line) and pressed (dashed 

line) films. 

4. Conclusion 

In this study, a new material, previously developed by researchers at ARL, was thermally 

pressed into a thin film and laminated onto a BDU fabric. This investigation demonstrates the 

ability to produce polymer/fabric composites using an environmentally friendly process (without 

the use of toxic solvents) that can easily be scaled-up to a larger production. This work 

addresses the need for the future development of CPC as an everyday lightweight garment 

opposed to current bulky protective overgarments. 
8

Future studies will be required to address several shortcomings in this study, such as reducing 

film thickness (for reducing weight), increasing adhesive strength between polymer and fabric, 

and developing practical procedures for scaling up this process. In addition, future experiments 

will need to be conducted to determine the durability (mechanical testing) and selectivity 

(transport testing) of the new polymer/fabric composite. 

5. References 

1. Lee, B. L., T. W. Yang, and E. Wilusz. “Moisture Effects on Isobutylene-Isoprene 

Copolymer-Based Composite Barrier. 1. Moisture Diffusion and Detection.” Polymer 

Engineering & Science, vol. 36, no. 9, p. 1217, 1996. 

2. Napadensky, E., Y. A. Elabd, J. M. Sloan, and D. M. Crawford. U.S. Army Research 

Laboratory, Aberdeen Proving Ground, MD, unpublished data. 

3. American Society for Testing and Materials. “Standard Test Methods for Mass per Unit 

Area (Weight) of Fabric.” ASTM D3776-96, West Conshohocken, PA, 1996.
9

Appendix A. Programmable Steps 

Table A-1. Program 1. 

Step Temperature Temperature Rate Force Force Rate 

(°C) (°F) (°C/min) (°F/min) (N) (kips) (N/min) (kips/min) 

Dwell Time 

(min) 

Go to 

Step 

1 107 225 13.91 25 4450 1 4450 1 5 1.2 

2 107 225 13.91 25 20000 4.5 20050 4.5 15 1.3 

3 37.8 100 13.91 25 20000 4.5 20050 4.5 2 1.4 

4 OFF OFF — — — — — — — — 

Table A-2. Program 2. 

Step Temperature Temperature Rate Force Force Rate 

(°C) (°F) (°C/min) (°F/min) (N) (kips) (N/min) (kips/min) 

Dwell Time 

(min) 

Go to 

Step 

1 107 225 13.91 25 22200 5 22200 5 2 2.2 

2 107 225 13.91 25 267000 60 88900 20 15 2.3 

3 37.8 100 13.91 25 22200 5 88900 20 2 2.4 

4 OFF OFF — — — — — — — — 

Table A-3. Program 3. 

Step Temperature Temperature Rate Force Force Rate 

(°C) (°F) (°C/min) (°F/min) (N) (kips) (N/min) (kips/min) 

Dwell Time 

(min) 

Go to 

Step 

1 48.9 120 5.6 10 267000 60 88900 20 20 3.2 

2 26.7 80 11.3 20 44500 10 88900 20 2 3.3 

3 — OFF — — — — — — — — 
10

Appendix B. Further Instructions 

• If any defects to films were found after visual inspection, additional powder was placed 

over defective areas and program 2 was repeated. This process can be repeated several 

times to ensure defect-free films.

• Pressing the powder using program 1 with only the Teflon∗ fluoropolymer sheet and caul 

plates will not work well. Pressing the powder without the rubber sandwich did not 

produce a workable film. However, it is possible to make one using repetitions of program 

2. Films produced this way will be much thicker than normal. 

• Use one sheet of Teflon whenever programs 2 and 3 are being run to improve the surface 

quality of the film. This will also help to prevent cracks and holes from occurring. 

• Do not press the fabric and film together in the rubber sandwich. This will destroy the 

fabric, the film, and the Teflon sheets. 

• Take care to ensure that the cylinders on the cryogenic grinder are tightly put together or 

powder will escape and be ruined. 

• Be patient spreading the powder. It needs to be as evenly distributed and uniform as 

possible. Take your time. 

• Use the razor blade to lift the edges of the film off the Teflon or caul plate before 

attempting to remove the film altogether. This will help to reduce the risk of tearing the 

film. 

• As stated in section 3 of this report, the film can be repaired using either powder or film as 

a patch. This will cause the film to spread out at the higher pressures at program 2 and may 

cause cracking. Use one Teflon sheet to help prevent cracking. 

• Pressure seems to be more important than temperature in this process. 

• A new application of 3–5 coats of Frekote†

 releasing agent is needed for approximately 

every three repetitions. 

• In general, this process works extremely well. However, it produces highly variable results 

in the time to complete a single film. On average, it takes 1 day to make and laminate two 

films. 

• Learning how to make the films, at this point, and being proficient is all trial and error.

 ∗

 Teflon is a registered trademark of E.I. du Pont de Nemours and Company. 

†

 Frekote is a registered trademark of Loctite Corporation. 
11

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4. TITLE AND SUBTITLE 

Thermal Processing and Composite Laminate Formation of Ionic Block 

Copolymers for Protective Clothing

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AH84 

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6. AUTHOR(S) 

James Harris, Yossef A. Elabd,* Eugene Napadensky, and Paul Moy

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*Yossef A. Elabd is a National Research Council Postdoctoral Associate.

14. ABSTRACT 

The future U.S. Army soldier will require lightweight, flexible, durable, and selectively protective clothing for the battlefield. Current 

chemical protective clothing is worn as an overgarment and is impermeable to moisture vapor, imposing unbearable amounts of heat 

stress on the soldier. A new material, an ionic block copolymer, developed by researchers at the U.S. Army Research Laboratory, is 

both flexible and a “breathable” protective barrier. This study focuses on thermally processing and laminating this new material onto 

the standard battle dress uniform (BDU). 

Polymer films were produced by cryogenically grinding the polymer to a powder and then thermally pressing it into a film. Films 

were pressed at 1.15 H 107 Pa (1668 psi) and 100 °C and were uniform in thickness, with thicknesses ranging from 254 to 300 μm 

(10–13 mils) from film to film. Films were then laminated onto a standard cotton/nylon BDU fabric using a similar pressure, but 

lower temperature (50 °C). The polymer/fabric composite nearly doubled the thickness of the fabric and increased the weight 

threefold. Additionally, infrared spectroscopy revealed no chemical change occurred in the pressed polymer films due to thermal 

processing.

15. SUBJECT TERMS

polymer processing, laminate formation, protective clothing, ionic block copolymer

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