Advanced Textile Laminates for Chemical Biological Protective Clothing

Eugene Wilusz l, Larry C. Wadsworth2

, Peter Tsai2, and Quoc Truong l

I US Army Natick Soldier RDE Center, Natick, MA2 University of Tennessee, Knoxville, TN

ABSTRACT

Much of the chemical biological (CB)protective clothing used by the military is basedon the use of activated charcoal as a majorcomponent of a composite textile system. Thisclothing does a good job in providing protection,however it is quite heavy, uncomfortable, andpotentially subjects the wearer to heat stress.Lightweight textile systems are underdevelopment to address these issues. Laminateshave been developed based on selectivelypermeable membranes as well as othersincorporating filter fabrics. These novelmaterials have the potential to provide CBprotection in lighter weight, more comfortableclothing systems.

1. INTRODUCTION

Today's chemical biological (CB)protective clothing does a very good job ofproviding protection against a wide variety ofthreats. In the civilian sector this clothing isused in numerous industrial workplaces and alsoby emergency responders. In these applicationsthe clothing is usually made from an air­impermeable barrier material such as athermoplastic polymer, elastomer, or coatedfabric. The CB clothing used by the military isbased on a textile system which has a degree ofair permeability to maximize comfort while stillretaining protection. An important component ofthe textile system is activated charcoal whichserves as a universal vapor adsorbent. In generalthese CB clothing systems are still too heavy,uncomfortable, and subject the wearer to thethreat of heat stress with prolonged usage andmoderate work levels. Materials research isunderway to develop lighter weight materials forthis purpose which will still retain appropriatelevels of protection.

One approach to lightweight materialsfor this purpose is the use of selectivelypermeable membranes (SPMs). Several SPMshave been developed which serve as effectivebarriers to hazardous chemicals and aerosols

while allowing a degree of moisturevapor transpOli (MVT). It is expected that theMVT will provide a measure of relieffrom heatstress through evaporative cooling. Surfacemodification techniques have been employed foroptimizing the properties of these SPMsincluding ion implantation and the addition ofLangmuir-Blodgett monolayers of cycliccompounds. The SPM concept is shown inFigure 1.

Figure 1. SPM Concept

A second approach is the use of alightweight filter fabric in combination with aliquid repellant outer layer and a vaporadsorptive inner lining. Expandedpoly(tetrafluoroethylene) (ePTFE) is a wellknown material for this application. Acombination of longitudinal and transversestretching of the PTFE membrane duringmanufacturing results in a lattice-like porousstructure of micro-sized interconnected fibrilsand nodes. The size of the micropores iscontrollable and is directly related to themoisture vapor transport of the film, which, intum, is related to comfort. Furthermore, theePTFE film and its adhered outer layers can beelectrostatically charged for maximum aerosolfiltration efficiency.

2. EXPERIMENTAL

2.1 Experimental for first phase of study

Laminates of ePTFE films withdifferent weights were placed between lightlypre-bonded spunbond (SB) polypropylene (PP)webs with weights of 20 and 50 g/m2 and bondedtogether by two advanced techniques. First abreathable adhesive was applied in a lined

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4. TITLE AND SUBTITLE Advanced Textile Laminates for Chemical Biological Protective Clothing

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pattern (4 lines/inch) to both sides of the ePTFEmembranes. Then the SB PP webs were appliedto each side, and the SB/ePTFE/SB laminateswere lightly compacted between smooth rollersand cured at 210 OF. Similar ePTFE membraneswere also laminated between 20 and 50 g/m2 SBPP webs and were subjected to thermalcalendering using a 2-roller B. F. Perkinsthermal bonder with a 260 line/inch engravedcalender roller. The combination of this newfine-lined engraved roller over a smooth steelroller was employed because this type of nip hasbeen recently found by industry to be well suitedto bonding fabrics with delicate textures andwith nano-polymer finishes. It was hoped thatthese two techniques minimized pin-holeformation during the bonding of the laminatesand reduced breathability less than moreconventional adhesive and thermal bonding.Then both types of laminates wereelectrostatically charged (EC) using Tantret™EC technology. It was believed that theseminimally evasive techniques for bonding thelaminates as well as the use of EC to improve thecapture efficiency of aerosols would result inimproved barrier, strength and comfortperformance of the laminates. The laminateswere characterized for mean pore diameter,filtration efficiency to sodium chloride aerosolparticles, hydrostatic head, and for moisturevapor transmission rate. Gross morphology ofthe laminates, including the ePTFE membranes,adhesive, and thermally bonded areas, wasanalyzed using scanning electron microscopy.

It is known that expanded­polytetrafluoroethylene (ePTFE) film is a goodbanier to chemicallbiological (CIB) aerosols,especially when used in combination with anunderlying adsorbent carbon layer in chemicalprotective liners for soldiers. A combination oflongitudinal and transverse stretching of thePTFE membrane during manufacturing results ina lattice-like porous structure of micro-sizedinter-connected fibrils and nodes (1-4). Thisstructure can be seen in the SEMphotomicrograph at 10,000X in Figure 2 of aDonaldson Company ePTFE film. However, thesoldier or first responder in an emergency orterrorist threat would be even more comfortableand effective if the water vapor transmission rate(WVT) of the ePTFE membrane in CIBprotective clothing could be markedly improvedto enable the individual to safely function in highheat-stress situations for extended periods oftime. Although the mean pore size and porosity

2

of ePTFE increases with increasing longitudinalstretching ratio, transverse stretching ratio, andheat-treating temperature, additional stretchingbeyond that here-to-fore found to be satisfactorymight result in a decreased level of performance.

The objective of this study is to provethat electrostatic charging (5-6) of the ePTFEmembrane or adhered outer polypropylene (PP)nonwoven layers with high dielectric propertiesshould substantially improve the ability of theePTFE membrane and its component layers toattract and thereby minimize the penetration ofaerosols in water or organic based aerosols or assolid particulate. The second hypothesis to proveis that electrostatic charging (EC) will enable themean pore size and over-all porosity of the filmto be increased by greater stretching of theePTFE film to provide substantially highermoisture transport and consequently greatercomfort.

Figure 2. SEM at 10,000 X of DonaldsonePTFE

2.2 First phase results and discussion

From the first phase of this study (7)our hypothesis that electrostatic charging (EC)the ePTFE film would increase the aerosolfiltration efficiency (FE) had mixed results. Itwas found that EC of non-finished and FChydrophobic finished ePTFE resulted in slightlydecreased FE to NaCI and DOP aerosols.However, the EC of laminates of ePTFE with SBPP generally resulted in an increase in FE. Withone laminate of spunbond (SB) PP/ePTFE/SB PP,EC resulted in a 7.3 fold decrease in penetrationofO.0671lm NaCI particles. This demonstratesthat the EC laminates of ePTFE and SB or meltblown (MB) PP fabrics promises to provideenhanced FE.

In an effort to improve FE of the ePTFEcomponent, the film was treated with one­atmospheric electrical plasma. However, theplasma treatment reduced the FE and ECtreatment further decreased FE. Stationary ECtreatment of ePTFE films alone was tried, aswell, for different lengths of time; however, FEdecreased notably with increasing EC treatmenttime. In addition, it was found that the ePTFEfilm had to be biaxially heat-stretched instead ofuniaxially to uniformly decrease film weight andthickness and to notably increase porosity. Aftermany unsuccessful attempts with the stretchingequipment at UT, we were able to have ePTFEfilms biaxially stretched uniformly at theAdvanced Engineering Fibers and Films(CAEFF) Center, Clemson University. CAEFFhas redesigned their T.M. Long stretcher andinterfaced it with a computer for more precisecontrol of films during heating and stretching.The ePTFE films were heat-stretched biaxiallyup to 2.2X. These ePTFE films were then ECand just as was found with the non-post­stretched ePTFE films, FE of the EC biaxially­stretched films decreased with EC. It did notappear to make a difference whether or not theePTFE film was treated with a fluorochemical(FC) prior to heat-stretching and EC.

2.3 Experimental for second phase of study

During this second phase of the study, laminatesof ePTFE films were placed between lightly pre­bonded spunbond (SB) polypropylene (PP) webswith weights of 20 and 50 g/m2 and bondedtogether by two advanced techniques. Lightlypre-bonded SB PP webs were prepared forlamination with ePTFE so that subsequentthermal point bonding would not cause thelaminate to be as stiff as if completely bondedSB PP was used because during thermal bondingofthe laminate, the SB PP is being subjected to asecond calendering process. In the first method,two laminates were prepared with both having acenter layer of ePTFE but one had an outer layerof 20 g/m2 SB PP on each side and the other had50 g/m2 SB PP on each side. They were bondedusing Performax 8535 applied to the SB PPnonwoven substrate via print application in orderto create a discontinuous deposit of the adhesiveon one side of the nonwoven substrate. A printpattern of thin stripes was used in order to leavea large "uncoated" area to enable high WVTthrough the composite. After printing theadhesive on the two layers of nonwoven, theePTFE film was placed between the two layers

3

of SB PP, the laminates were then pressedtogether between two cold smooth steel rollers at1,000 psi, and immediately dried/cured in anoven at 220-225 of for 3 minutes (8).

In the second laminating technique,ePTFE membranes were laminated between a 20g/m2 SB PP on one side and a 50 g/m2 SB PPweb on the other side and these composites weresubjected to thermal calendering using a 2-rollerB. F. Perkins thermal bonder at The Universityof Tennessee Nonwovens Research Laboratory(UTNRL) with a Schreiner diagonally ribbed rollwith 260 line/inch (Figure 3) at a surface speedof 1.5 rn/min with a roller surface temperature of275 of and a bonding pressure of 150 PLI. Thecombination of this Schreiner roller over asmooth steel roller was employed because thefine ribs do not penetrate as much into thesubstrate as do typical diamond patternedengraved calendar rollers (9). It was hoped thatboth the special adhesive bonding and thelmalbonding techniques employed minimized pin­hole fOlmation dUting bonding the laminates andreduced breathability less that more conventionaladhesive and thermal bonding. Then both typesof laminates were electrostatically charged (EC)using Tantret™ EC technology. It was believedthat these minimally evasive techniques forbonding the laminates as well as the use of EC toimprove the capture efficiency of aerosols wouldresult in improved barrier, strength and comfortperformance of laminates which could be used inchemical protective liners for soldiers. Thelaminates were characterized for mean porediameter and for water vapor transmission rate(WVT) according to ASTM E 96/E 96M-05,Desiccant Method, Procedure E at 37.8 °C and90% RH. Gross morphology of the laminates,including the ePTFE membranes and adhesiveand thermally bonded areas, was analyzed usingscanning electron microscopy.

2.4 Second phase results and discussion

Figure 3. Thermal bonding with a) feeding ofun-bonded laminate of 50g SB PP on top fordirect contact with 260 line/in. Schreiner roll,ePTFE in center, and 20g SB PP on bottom forcontact with smooth steel roller and b) thermallybonded laminate exiting calender nip

In Table I, the WVTs of the non-electrostaticallycharged (NC) adhesively bonded laminates ofePTFE with SB PP ranged from 5,448 with theT2 ePTFE with outer layers of 50 g/m2 SB PP to5,711 g/m2/day with the ePTFE with lighter thelighter 20 g/m2 SB PP webs, although theseWVT values are rather close. The WVTs of thecorresponding EC laminates were 5 998 to 6 365

2 ' ,g/m /day, with the lighter outer SB layersapparently resulting in slightly greater WVTs.However, all of these samples had the same coreofT2 ePTFE, which primarily contributes tobarrier properties, while still allowing relativelyhigh WVT. The mean pore diameter of the T2ePTFE was 0,48 f..lm before lamination andincreased to 1.1 0 and 2.09 f..lm after adhesivebonding with the outer SB PP layers. The lattermean pore sizes are still rather small, but someweb distortion or pinhole formation may haveoccUlTed during hot pressing of the adhesively­bonded laminates prior to curing of the adhesivein the oven.

adhesive or thermally bonded laminates of SBPP with ePTFE. The porosity of these samples istoo low to determine filtration efficiency to0.067 f..lm NaCI particles using the TSI Filtertester at the University of Tennessee. The meanpore size of ePTFE used in thermally bondedSample 5 was 0.37 f..lm before thermalcalendering and increased to 1.61 f..lm afterbonding, indicating some fabric distortion orpinhole formation as a result of calendering. Onthe other hand, Sample 7, which had a differentePTFE film with a mean pore size of 0.27 f..lmbefore bonding, had an unchanged mean porediameter of 0.30 f..lm after calendering using theSchreiner roller. In comparison, the thermallybonded laminate of SB PP and ePTFE obtainedfrom a commercial source (Sample 9) had amean pore size of3.50 f..lm, and a WVT of6 235

2 'g/m /day before EC and 6,025 g/m2/day after EC.

SEM analyses revealed that the fibrousstructure of the outer SB layers of both theadhesive and thermally bonded was largely intact.It was surprising however, that the outer SB PPfibers of the adhesively bonded laminates wereflattened (Figure 4) in both the non-adhesive areaand in the adhesive sttipe. It is possible thatalthough the SB PP webs were only lightlycalendered when they were prepared, that theflattened fibers resulted from the firstcalendering step on the SB line. Also thepressure of 1000 psi may have been too great inpressing the laminate together between smoothrollers prior to being placed in the oven at 220­225 OF for 3 minutes. The oven exposure waswell below the temperature range of250 -265 OF,at which PP can begin to undergo thermalshrinkage. Although the laminates bonded usingthe Schreiner roll/smooth roller nip had generallyround outer SB PP fibers, there was an indicationthat some fibers had melted and fused fiberstogether (Figure 5). In comparison, a thermallybonded laminate of SB PP and ePTFE, Sample 9,obtained from a commercial source had manyflattened SB PP fibers on the surface, apparentlyfrom the thermal bonding step (Figure 6).

b) Thermally bondedlaminate

a) Feeding in un­bonded laminate

The WVTs of the NC thermally bondedlaminates of ePTFE with SB PP ranged from4,632 to 5,403 g/m2/day with the correspondingEC laminates having values from 5010 to 5822

2 ' ,g/m /day. A clear trend could not be seen withrespect to the effect of EC on WVT of either the

4

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b) Thetmally-bonded sample 5 at lOOX

b) Adhesive bonded strip of Sample I at500X

Figure 5. SEM photomicrographs of thermally­bonded sample 5

Figure 4. SEM photomicrographs of adhesive­bonded sample I in adhesive strip and in non­adhesive area

laminating and bonding by thermal or breathableadhesive methods.

CONCLUSIONS

Textile laminates have been fabricatedand shown to be feasible materials forconsideration in the next generation oflightweight, CB protective clothing. Additionalwork is planned to optimize these materials.

The findings from the first phase of thestudy would be employed concerning post­stretching and laminating ePTFE with highlydielectric, yet strong materials on both sides such

. as spunbond (SB) PP, melt blown (MB) PP, andMB/SB composites, which can beelectrostatically charged before or after

On a larger scale (50 to 200 meters with awidth of 0.5-2 meter) of commercial ePTFEfilms with different weights and mean poresizes it would be possible to fust post-heatstretch the ePTFE film and could utilize tenterframes such as thoseat North Carolina State University in Raleigh orat Precision Fabrics in Greensboro, NC to bi­axially post-heat-stretch ePTFE film to differentweights, thicknesses, and mean pore diameters.

Much smaller diameter SB PP webs (8-12flm) would be produced at Hills, Inc., Melbourne,FL or on the 1.5m wide SB line at OerlikonNeumag Nonwovens in Neumunster, Germany

5

Figure 6. SEM photomicrograph of DonaldsonThermally-Bonded Sample 9

and micro-diameter MB webs will be producedon the 0.5 meter MB line at TANDEC (nowcalled UTRNL). The different SB and MB PPwebs will be laminated with single and multiplelayers of non-post stretched and post-biaxially­heat-stretched commercial ePTFE films. Half ofthese laminates will the thermally point-bondedand the other half will be adhesively bonded.For thermal bonding, the new 0.5 meter B.F.Perkins calender at UTNRL with differentbonding patterns will be utilized. For adhesivebonding, a company such as Lubrizol, Gastonia,NC, could be employed to produce batch andcontinuous samples. Care would be taken not todeform the SB PP fibers while compressing thelaminates after application of adhesive betweensmooth rollers. It would also be determined if itis better to electrostatically charge (EC) the SBand or MB PP outer layers separately beforelamination or after lamination andbonding. Even ifEC of the ePTFE laminateswith different weights and fiber diameters of SBand MB and combination SB and MB outerlayers does not notably increase, it is believedthat using multiple layers of thinner ePTFE films(obtained commercially or by post-stretching bythese researchers), which are then adhesive andor thermally bonded with SB, MB or SB/MB PPnonwovens will result in greater WVT thanensembles with one thicker layer of ePTFE ofthe same weight.

Mig" 1.00KX '......1--1EHT- 3.00WWO- 3mm

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having supplied ePTFE membranes andlaminates. The authors are further indebted toLubrizol, Inc. for adhesively bonding laminatesof ePTFE with 20 and 50 g/m2 SB PP producedbyUTNRL.

REFERENCES

1. Purinton, N. and S. Filter, "Gore-Tex:An Introduction to the Matetials andTreatments," The Book and PaperGroup Annual, Volume Eleven, 1992,The American Institute forConservation fromhttp://aic.stanford. edu/sgfbpg/annual/v 11/bp11-33.htrnl.

2. Fabric1ink performance fibers andfabrics fromhttp://www.fabric1ink.comlpk/indexfab2.html.

3. Jizhi, H., J. Zhang, X. Hao and Y. Guo,"Study of a Novel Process for Preparingand Co-stretching PTFEIPU Membraneand Its Properties," European PolymerJournal1Q, 667-671 (2004).

4. Hao, X., 1. Zhang, and Y. Guo, "Studyof New Protective Clothing againstSARS Using a Semi-PermeablePTFEIPU Membrane," EuropeanPolymer Journal1Q, 673-678 (2004).

5. Tsai, P. and Wadsworth, L., "Methodand Apparatus for the ElectrostaticCharging ofa Web or Film," US Patent5,401,446, Mar. 28, 1995.

6. Wadsworth, L.c. and P.P. Tsai,"Method and Apparatus for theElectrostatic Charging of a Web orFilm," U.S. Patent 5,686,050, Nov. 11,1997, assigned to UTRF.

7. Wadsworth, L.C. (Speaker), E. Wilusz,Q. Truong, and P.P. Tsai,"Improvement of Barrier and comfortProperties of ePTFE Membranes andComposites," AATCC IC&E, Materials

8. Track Sessions, Charleston, SC,October 1-3,2007.

9. Scott, J., Lubrizol, Email Letter to L. C.Wadsworth, April 7, 2008.

10. Gunter, S., Engraving LLC, Sandston,VA, Private Communication with L. C.Wadsworth, March 31, 2008.

ACKNOWLEDGEMENTS

DeWalindustries, Inc., GE Energy Systems, andDonaldson Company are acknowledged for

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Table 1. Weight, Thickness, Mean Pore diameter and WVT of Adhesively and Thermally BondedLaminates ofePTFE with SB PP Webs.

NC - Not Electrostatically Charged2EC = Laminate Electrostatically Charged

Sample Description Weight Thickness Mean Pore WVTNo. (g/m2

) (mm) Diameter (g/m2/Day)

him)Film LamOnly

ADHESIVE BONDED(AB)

1 NC t AB with core of 73.4 0.280 0.48 1.10 5,711Taiwan (T2) and outer

20gsm SB PP2 Same as 1 but EC L 77.7 0.307 6,3653 NC AB with core ofT2 and 120.6 0.478 0.48 2.09 5,448

outer 50gsm SB PP4 Same as 2 but EC 121.9 0.567 5,998

THERMALLY BONDED(TB)

5 NC TB with 50gsm SB 88.3 0.145 0.37 1.61 5,403PPlDonaldson (D)

ePTFE/20 gsm SB PP6 Same as 5 but EC 87.1 0.136 5,0107 NC TB with 50gsm 0.27 0.30 4,632

SB/GEH ePTFE/20gsm SB8 Same as 7 but EC 92.2 0.136 5,8229 NC Donaldson AX 05-159 53.5 0.197 3.50 6,236

Lam of ePTFE and SB PP10 Same as 9 but EC 57.2 0.214 6,025

-

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14. COMMENTS:

PAO comments:Page 2, para. 2.2, last sentence, "This demonstrates that the of EC laminates of ePTFE... " Either the word "of" needs to come out or thereis a word missing. Check.Page 3, para. 2.3, Ist sentence, "During this second...of ePTFE films with were placed... " Either the word "with" needs to come out orthere is a word(s) missing. Check.Same para., 9th line, should there be a period at end of sentence after the word "bonded"?Page 3, last para., 19th sentence, "hole formation during bonding the laminates and" - I think you need the word "of" between the words"bonding" and "the."Comments cont'd on forwarding email

NATICK FORM 1613, DEC 2007 ThiS replaces NATICK FORM 1613, dated SEP 2007, which IS obsolete. Page 1 of 3