Indian Journal of Fibre & Textile ResearchVol. 22, June 1997, pp. 94-98

Efficient and quick method for evaluation of carbon-coated breathableprotective clothing for toxic chemicals

V S Tripathi, Darshan Lal & A K Sen

Defence Materials & Stores Research & Development Establishment, DMSRDE P.O., G T Road,

Kanpur 208013, India

Received 18 March 1996; revised received 16 October 1996; accepted 12 December 1996

An efficient and quick method for evaluation of breathable fabric is described. The method is based onmeasurement of penetration time of 1,3-dichloropropane (DCP) using the portable diffusion test equipment(DTE) developed at DMSRDE. DTE comprises of a diffusion cell, a single-flame flame ionisation detector(FID), a digital rnilivoltrneter and a timer. All these components are fitted in a 25x50xlO em box alongwith the required controls. The calibration procedure and the working of the instrument are described insome details. The results obtained using the conventional method and the new method/apparatus developedhave shown better than 99.5% correlation on regression analysis. Air permeability of different fabrics hasalso been recorded.

Keywords: Carbon-coated breathable protective clothing, Dichloropropane, Diffusivity, Air permeability,Protective clothing

1 IntroductionDue to comparatively low-heat stress, breathable

carbon-coated fabric is preferred over impermeablepolymer-coated fabrics for protection against toxicchemicals which cause injury by adsorption throughskin. Various methods adopted worldover forevaluation of breathable fabric make use of liveagents, e.g. mustard, and are time consuming1

-3• In

most of the test methods, colour development in adetector paper is used for monitoring thebreakthrough of chemical agent and this induces anelement of subjectivity. Moreover, the use of toxicchemicals at production site for fixing andoptimization of operating conditions of the plant andquality control creates safety problems. It may alsobe pointed out that due to non-uniform distributionof the carbon particles and presence of binder, thecharacterization methods based on equilibriumadsorption techniques, such as surface areameasurement and pore size distribution, do notindicate the performance ofthe fabric.

In view of these problems, a protable diffusiontest equipment has been developed in this laboratoryfor rapid quality control of the breathable fabricusmg a simulant and gas chromatographictechnique. The breathable fabric used is active

carbon-coated fabric and the simulant used is 1,3-dichloropropane (DCP) in lieu of S-mustard used instandard methods. DCP is chosen as a simulantbecause it has some similarity in structure with S-mustard, e.g. two terminal chloro groups. DCP has alow boiling point and is easy to detect by gaschromatographic detectors. Important properties ofmustard and DCP are shown in Table 1. It may beseen that the DCP penetration time correlates fairlywell with mustard breakthrough time. Thisequipment has been particularly useful for qualitycontrol, at the production site, of carbon-coatedfabric.

Table l=-Physical properties of HD mustard and1,3-dichloropropane

Property Mustard 1,3-DichloropropaneCH2CH2CI CH1CII I

Chemical formula S CH1

I ICH2CH2CI CHoCl

"Size (diam.) 6.97 A 6.40 ADensity at 20°C 1.186 g/cc 1.275 glccBoiling point 118°C 217°CMolecular weight 159.08 112.99

"Size evaluated using equation 1.09 (MlpN)v3

TRIPATHI et al.: CARBON-COATED BREATHABLE PROTECTIVE CLOTHING 95

In this paper, the design of diffusion testequipment, its method of calibration, correlation ofmustard breakthrough time with DCP penetrationtime and its advantage in rapid and accurateevaluation: of carbon-coated fabric are described.

2 Materials and MethodsThe diffusion test equipment is based on gas

chromatographic technique. The GC columnseparating the components of a vapour by partitionis however replaced by a diffusion cell. Penetrationtime of the simulant 1,3-dichloropropane across thepolyethylene film and breathable carbon-coatedfabric is detected and measured by flame ionisationdetector.

2.1 MaterialsPure dry nitrogen (Indian Oxygen Limited, India)

was used for primary calibration and as carrier forsecondary calibration and testing. 1,3-dichloropropane (Aldrich Chemical Co, USA) of99.5% purity was used for measuring penetrationtime. Low-density polythene blow films of 13 urnand 50 urn thickness were procured locally.Protective clothing samples were made by coatingdough (carbon + neoprene binder) using knife onroller technique on nonwoven fabric. Base fabriccomprised of polyester wadding and plane weavepolyester/cotton scrim attached together byneedling. Base nonwoven fabric (95±5 g/m") had airpermeability of 250 cm ' Icm2 Is at 5 mm water head.Fabric samples A-G having different carboncontents were prepared by varying the operatingparameters such as carbon to binder ratio, doughviscosity, traverse rate of fabric, etc. The details ofmethod and materials of coating are not reportedhere as a patent application has been filed on theprocess of coating.

, 1 Oiffu••ion Test Equipment ID'\'[)

Portable DTE assernbiv CGfI'\f:r.;,,3 .)'-l.;,.f'.SJ0n

cell, single-flame Fill, mass iO'V contrcll-rs, digitalmillivoltmeter, timer an +wi-stage attenuator. Ifultra pure hydrogen is used as ruel and nitrogen ascarrier, single flame FID gives adequate sensitivity,The usual recorderlintegrator has een rcnlaced by adigital millivoltmeter and a .irner C' iltn theapparatus. Timer used in DTE has been '1esigned inJd' a ,vay "'~'3tit stons as the digital rrnlhvoltmetereaches one nilirvolt r eading. Mass How controllerse used f~.~:.'le<cntr-. of carner » id he gas How.

The DTE assembly can be packed in a 24 in.suitcase and can be carried to the test site as andwhen required.

The diffusion cell (Fig. 1) comprises of two brasscylinders having 52.0 mm hole at the centre. Theupper cylinder has a through hole and acts ashousing for test cup containing DCP source. Thelower cylinder having 3 rom deep groove providesthe area to be swept by the carrier gas. A 13 urnpolythene film covered with wire mesh issandwiched between the two cylinders. Thediffusion cell is connected to FID with 1116 in.stainless steel tubing. The test cup comprises of 3mm thick spacer placed over breathable fabricfollowed by Whatman No. 1 filter paper and 1 romthick spacer. The diffusion cell is installed in the DTEapparatus casing to retain the portability of theequipment. The cell is heated to 30°C using cartridgeheater and temperature controller and is properlyinsulated to maintain temperature during testing.

2.3 CalibrationThe set-up used for primary calibration is shown

in Fig. 2. Pure dry nitrogen stream from cylinderwas split in two parts and passed throughprecalibrated capillary flow meters. One stream of

:,TOPPER -------~t mm SPACER -- -----.~"7 _2mm SPACER ------c:::::J r::::=::JSAMPLE ~. • ITEST CUP -~---.I

TEST CUP ASSEMBLY

F'LHR PAPER

[;'l ill:: ; I,I , •

:: ::---- -=~~--- ---- -------- : ;

BRASS DIFFUSIONCELL TOP

Fig. I-Diffusion cell

VENT

Fig. 2-Schematic diagram for calibration of diffusion testapparatus [l-Capi\lary flow meter; 2-Saturators; 3-Thermostat ; and 4--Mixing coil]

96 INDIAN J. FIBRE TEXT. RES., JUNE 1997

nitrogen was passed through a bubbler (containingDCP) maintained at O°C at the flow rate of 1mL/min. The saturated stream was further dilutedwith the second stream at the rate of 1 Llmin. Thismixed stream after homogenisation in 2 m longcolumn was sent to FID at the ratio of 10 mLimin.The rest of the stream was vented out. This flow ratecorresponds to 1 ,ug/min of 1,3-dichloropropane.The sensitivity of the instrument was then adjustedin such a way that it gave 1 mV reading consistentlywhile DCP laden nitrogen flew through FID. TheDCP concentration was calculated using followingequation:

g PM=

v RTwhere g is the DCP present (in grams) in v ml ofnitrogen; P, the saturated vapour pressure of DCPat T'K; M, the molecular weight of DCP; and R, thegas constant.

Once the primary calibration was achieved, thearrangement used in Fig. 2 was disconnected and apolythene film of 50 urn thickness was placed in thesample holder without changing the sensitivity ofinstrument. DCP penetration time was thenmeasured through the film by the timer at 1 mVreading. A set of polythene films from differentplaces of the same roll was chosen and penetrationtime of different films recorded (Table 2). The meanof six readings was taken for a film, and the filmwhich was found to have penetration time nearest to85 s was taken as standard for secondary calibrationfor subsequent day to day work.

Permeation time of different films samples cutfrom the same roll varied widely due to the variationin thickness of polythene films from point to point.However, the standard deviation for the same filmwas quite small and DCP penetration time was quitereproducible.

After calibration, the apparatus was ready fortesting of protective breathable fabric. Theparameters of primary and secondary calibration andthe procedure of testing of breathable fabric is as perthe UK specification'. Acceptability criteria for aroll of fabric is also laid in the specification.Accordingly, the average of DCP penetration timefor six samples in the given set of conditions shouldnot be less than 45 s and no single reading should beless than 40 s.

2.4 ProcedureThe instrument was switched on and the flow rate

of H2 and N2 measured carefully. Compressed airafter passing through air purifier was fed to FID forburning the flame. The apparatus was kept on for anhour for stabilization before use.

As it has been mentioned that primary calibrationis not possible in routine testing, as such secondarycalibration was carried out. Previously tested 50 .urnthick polythene film was placed in the test cup andthen kept in the diffusion cell for 5-10 min to attaintemperature equilibration.

Five micro-litre of 1,3-dichloropropane was thendropped over the filter paper and covered with astopper to minimise loss of DCP from the cell.When the average of six readings was around 85 s,the apparatus was considered calibrated and readyfor testing. A piece of breathable fabric was thenplaced in place of 50 .urn polythene film and DCPpenetration time measured in the same way.

3 Results and DiscussionCarbon-containing fabrics should have two

important properties. Firstly, it should reduce thechallenge concentration of CW agent such thatcumulative dose never crosses intermediateincapacitating dose in say 24 h (ref. 7). Secondly,

Table 2-Penetration time of different films

Film Penetration time(s) readings Mean StandardNo. deviation

2 3 4 5 6

1 83 79 81 82 82 82 81.4 1.432 72 76 70 70 73 72 72.1 2.233 95 90 95 92 91 90 92.1 2.314 89 86 92 92 90 88 89.5 2.345 80 88 84 83 85 81 84.5 2.426 92 98 99 99 95 93 96.0 3.097 82 88 82 82 78 80 82.0 3 ..14._-._--------------

TRIP ATHI et al.: CARBON-COATED BREATHABLE PROTECTIVE CLOTHING

the air permeability of fabric should be high so thatphysiological stress is minimum.

In case of bis (dichloro-diethylsulphide), theagent recommended for testing, the medianincapacitating dosage (IC50t) is 2000 mg rnin/M'.Accordingly, for exposure to air saturated withvapour of above agent a sample should givebreakthrough time (BIT) of around 3 h at 20°C. Onthe other hand, the air permeability should beminimum 30 mL/cmlmin. The binding of carbonparticle on the fabric substrate should also be properfor the retention of functional properties as well asfor aesthetics. The carbon-coated fabric is acomplex system and the characteristics of carbonparticles, nature of base fabric, the type of the binderand the coating conditions are to be properlyoptimized to get the desired properties in the fabric.The retention of pollutants on the fabric isdetermined mainly by surface properties of carbon,its particle size, concentration of binder and thedistribution pattern of carbon on the fabric. Thebinder is usually an elastomer. For selecting asimulant, its nature of permeability through theelastomeric binder is an important consideration.Thus, any chemical used as simulant should havethe same type of interaction with binder andmechanism of removal by carbon should also bephysical adsorption without any specific interactionas in case of actual agents. The test agent 1,3-dichloropropane meets both these requirements.However, due to low molecular weight itsadsorbability is low and hence breakthrough occursin much shorter time compared to that for mustard,the usual test agent. A typical breakthrough curveobtained from DTE apparatus using the timer isshown in Fig. 3. Some results of DCP penetrationtest conducted during development work are givenin Table 3. It may be seen from the data that

97

standard deviation in DCP values is very low. Themustard breakthrough time for the same pieces offabric is also given in Table 3. The result shows thatthe standard deviation in mustard BIT value is quitehigh, probably due to subjectivity in the estimationof time of colour development.

According to the British specification", in case ofacceptable fabric the average of 6 readings shouldbe 45 s in the standard conditions and no singlespecimen should give less than 40 s reading. Thevalue of minimum DCP penetration time in ourcorrelation exercise was slightly lower than thisvalue, probably due to the differences in the

10 /2 !1, ,, ,, ,09 , ,, ,,

I, ,, ,0·8 , ,,, ,, ,

Carbon - CoatE'd: PolythE'nE' ",07 Fabric , ,, ,, ,, ,I ,

0·6 , ,,, ,,, ,: I

05 ,,, ,> , ,E I

,I I

04 , I

I I

I II I,

{I0·3 { {

I {

I I{ {

,02

,{

II

I

01 I

II

I

a , , I I I

0 10 20 30 40 50 GO 70 BOLime ,s

Fig. 3- Typical permeation curve of DCP through polytheneand carbon fabric

Table 3-CompanSon of mustard and DCP vapour diffusion tests

Air Mustard tes OCP testpermeability Mean SD Mean SD

at JOmm penetration min penetration swater head time, min timecm3/cm2/s s

55 62.2 13.2 17.2 I.3

52 78.6 16.3 19.0 1.141 145.6 18.5 33.7 1.650 164.6 14.6 51.8 I.344 107.2 31.9 23.3 1.0

52 90.3 46.6 18.3 0.766 172.2 15.2 74.8 2.3

FabricNo.

ABCDEFG

98 INDIAN J. FmRE TEXT. RES., JUNE 1997

polythene films used as barrier to separate the twoparts of diffusion cell. The regression analysis ofmustard BIT and DCP penetration time of differentfabrics given in Table 3 leads to followingregression equation:lID BIT=O.4477 DCP penetration time-18.4472

Correlation coefficient = 0.99158It may be stated from above that DCP penetration

time can be used as a parameter for evaluation ofbreathable fabric with full confidence.

4 ConclusionThe portable DTE apparatus, used successfully in

development work of breathable fabric, involvesdiffusion across the breathable carbon-coated fabricand polymer barrier. It could be used for difusionmeasurements of various organic compoundsthrough variety of barriers. Use of FID forquantification after diffusion enhances the speed andaccuracy of the instrument.

AcknowledgementThe authors are thankful to Prof G N Mathur,

Director, DMSRDE, for encouragement during thecourse of this work. They are also thankful to NuconEngineers, India, for assembling the apparatus.

ReferencesOudmayer H F G & Wihon P P M M, TNO report PML1991-92 TNO (Prins Maurits Laboratory, Netherlands),November 1991, 16.

2 Laboratory methods for evaluating protective clothingsystems against chemical agents, US Tech Report No.CRDC-SP-84010, 1984.

3 Specification cloth bonded multilayer, ANTIGAS Britishspecification No. UK/SCl3346 G (1982).

4 Barrer R M, Diffusion in & through solids, 2nd edn(Cambridge University Press, Cambridge), 1951.

5 Crank J, The mathematics of diffusion, 2nd edn (ClarenderPress, Oxford), 1975.

6 Singh B, Baronia S M, Nath R, Suryanarayana M V & RaoN B S N, Res Ind, 39(3} (1994) 165-169.

7 Jane's NBC protection equipment handbook, edited by TerryJ Gander (Jane's Data Division, UK), 1993-94.