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AD-A263 225

THE VERTICAL AND HORIZONTAL

WICKING OF WATER IN FABRICS (U)

by

Rita M. Crow and Malcolm M. Dewar

?~~'TICAPR 26 m M

93-085561111111111111111111lI

DEFENCE RESEARCH ESTABLISHMENT OTTAWATECHNICAL NOTE 93-3

Canada ,,PVT~sm m a w Ottawa

93 -1 018

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AB8TRACT

This paper examines th e ver t i ca l and hor izonta l wicking ormovement of water along a s t r ip of t ex t i l e material , a commonmethod of evaluat ing th e wicking behaviour of fabr ics . It wasfound t ha t th e fabrics of th i s study contain imperfectcap i l l a r i e s , with no one property, other than gross surfacecharacter is t ics , universal ly contr ibuting to t h e i r wickingbehaviour. It was concluded t ha t th e wicking behaviour of eachfabric must be determined individually.

RESUME

Ce rapport decr i t l'examen de l'effet meche ver t i ca l etlongitudinal de l 'eau d'une l i s i e re de t i s su . Il s'agit d'unemdthode commune pour l ' eva luat ion du comportement de l'effetm~che de s t i s sus . Cette 6tude nous a permis de decouvrir que le st i s sus analyses contiennent de s cap i l l a i r e s imparfai ts . Aucunepropridte physique ne contr ibue au comportement de l'effet dem~che des t i s sus , a l ' exept ion des carac ter i s t iques de la surfacebrute. Nous avons conclu que le comportement de l'effet meche dechaque t i ssu do i t & t r e determine individuel lement .

DTIC QUALM INUZCTED

Acoession For

ITIS GRA&,

DTIC TA BUnannowiedJustificatlon

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Availability CodeslAvail tand/9 r

iii le t Ispecial

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EXECUTIVE SUMMARY

The movement or wicking of water in fabr ics is of currenti n t e res t because of th e recent introduction of f ibres , yarns andfabrics which manufacturers claim impart grea t personal comfortto th e wearer. This comfort is said to be due to th e f ibre, yarnor f ab r i c ' s abi l i ty to wick perspi ra t ion away from th e skin,leaving th e wearer dry and warm. As pa r t of an on-going study onth e movement of water in and through t ex t i l e materlais , tn i spaper examines th e ver t i ca l and horizontal wicking of water alonga s t r ip of t ex t i l e material , a common method of evaluat ing th ewicking behaviour of fabrics .

Seven fabrics of varying f ibre content and physicalproper t ies were examined. The majori ty of th e fabr ics wicked

s imi lar ly to theore t ica l cap i l l a r i e s , with th e water movingquickly along th e fabric and then slowing up with time. This wasth e case whether gravity was involved or not, i . e . whether th esample was ver t i ca l or horizontal . However, only in two t e s t s didth e fabr ics wick according to th e c las s i ca l equation fo r l iquidmovement in cap i l l a r i e s . It was concluded t ha t t ex t i l e fabricscontain imperfect cap i l l a r i e s , with no one property, o ther thangross surface character is t ics such as "troughs" on th e surface,universal ly contr ibuting to t he i r wicking behaviour. Therefore,th e wicking behaviour of each fabric must be determinedindividually, ra ther than being predicted from th e class ica lwicking equation.

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INTRODUCTION

The movement of l iquids in fabrics by wicking (as opposed toby pressure) is of current i n t e res t because of th e recentintroduction of f ibres , yarns and fabrics which manufacturersclaim impart grea t personal comfort to th e wearer. This comfortis said to be due to th e f ibre , yarn or f ab r i c ' s ab i l i ty to wickperspi ra t ion away from th e skin, leaving th e wearer dry and warm.As pa r t of an on-going study on th e movement of water in andthrough t ex t i l e materials (1,2,3), th is paper examines a commonmethod of comparing th e wicking behaviour of fabr ics , namely, th ever t ica l and horizontal wicking of water along a s t r ip of t e x t i l emater ia l . It is noted t ha t th is method may be more applicable tomaterials in heat pipes or kerosene lanterns than to clothing.

Review of Litera ture

Harnett and Mehta (4) compared various laboratory testmethods fo r measuring wicking. They concluded t ha t measuring th ewicking heights in various fabrics only gives some indicat ion ofth e ra te of advance of th e l iquid front and would be morevaluable if l inked with mass t ransfer ra tes .

Minor and Schwartz (5) give the equation fo r th e rate atwhich a l iquid front advances in a fabric where th e effec t ofgravity is negligible as

s = kt1 /2

where s is th e distance t ravelled, t th e time and k th e constantcharacter is t ic of th e yarn-l iquid system. The p lo t of t h i sequation is shown in Figure 1. They theorized t ha t high twistyarns or plied yarns should wick water fur ther along th e fabric .

Time

Figure 1. Theore t i ca l wicking behaviour in capillaries.

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Holl ies e t a l (5) studied th e capil lary t ranspor t in yarnsand found t ha t it followed th e above class ica l relat ionship fornylon yarns which varied in twis t , number of f ibres and meancapi l la ry radius. They then took yarns taken from nylon, wool andwool blended serge fabrics and varied t he i r twis ts . They foundt ha t a t low (20 twists /10 cm) and high (120 twists/10 cm) yarn

twis ts , th e water t ranspor t rate was lower than a t th eintermediate values (40 twists /10 cm). At th e lower twists , theyconcluded t h i s was caused by a substant ia l reduct ion in numberand continuity of i n t e r f ib re cap i l l a r i e s . At th e higher twis ts ,th e capi l la ry spaces between th e yarns would approach zero, thusretarding th e flow of water along th e yarn.

In Par t II of t he i r paper (6), they examined th e horizontalwicking character is t ics of a range of fabrics . They found thatth e amount of water transported by a fabric depends on its water-holding capacity and on th e ra te with which th e water t ravelsthrough th e fabric. They again found t ha t there is a linearre la t ionship between th e square of th e distance t ravel led and

time. They also found t ha t not a ll of t h e i r curves passedthrough th e or ig in . They measured th e water t r anspc r t in yarnstaken from th e fabric and found th e wicking behaviour to besimilar. They concluded t ha t th e effec ts of change in yarntwist , f ibre denier and yarn size would also be evident in th ewater t ranspor t ra tes of th e fabrics . They found tha t th e woolblends tended to have lower water t ranspor t rates than fabrics ofa ll synthet ic or cotton content . They at t r ibuted th is to th erandom arrangement of th e wool f ibres in th e yarns. In a secondser ies , they compared th e wicking of acryl ic/wool blends andcould not predic t th e wicking propert ies . They concluded thatt h i s was due to th e f ibre randomness.

Method

To measure th e ver t ica l and horizontal wicking of th efabrics , a sample holder was made consist ing of a row of commonhousehold pins mounted at intervals of 0.25 cm in a s t r ip of 0.3cm thick plexig lass so t ha t t he i r points protrude about 0.5 cm.Each pin was connected to a computer-controlled data acquis i t ionrelay assembly. The resistance between th e first or common pinand each of th e other pins were measured and recorded by th ecomputer a t a prese t sampling ra te . When th e wicking waterreached any pin beyond th e common pin, t h i s event was marked byan abrupt drop in res is tance . The number of pins monitored andth e sampling rate could be varied to match th e wicking proper t iesof th e fabric . For fas ter wicking fabrics , more pins weremonitored and th e sampling rate increased. Typical ly, 12 to 15pins were monitored a t ra tes from I to 120 pins per minute. Theexperiment was terminated when th e water had wicked along th esample about 25 to 40 mm or a f t e r about 25 minutes, whicheverhappened first.

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P r i o r to th e exper iments , th e samples were cond i t ioned fo ra t l e a s t 24h in a room having the atmosphere c o n t r o l l e d at 20Cand 65% r e l a t i v e humidi ty (R.H.). The exper iments were also donein this room. A f a b r i c sample, 2.5 cm wide and 10 cm long wasmounted on th e sample ho lde r so t h a t th e pins pene t ra ted th esample on its cen t re l i n e . Care was taken to make sure th esample d id n o t touch th e p l e x i g l a s s . Rela t ive p o s i t i o n s weread us ted so t h a t 1 cm of th e sample was immersed in distilledwate r and th e wate r l e v e l wa s a t th e common p in . The computerwas a c t i v a t e d as th e wate r s t a r t ed to wick up or a long th e f a b r i cstrip.

The h o r i z o n t a l wicking exper iments were done in s imi la rf a sh ion with th e sample holder ro ta ted to a h o r i z o n t a l attitude.It was sometimes necessary to d i r e c t the lower en d of th e sampleinto th e wate r by means of a rubber band around th e en d of th ep l e x i g l a s s an d over th e sample.

The f a b r i c s used were from Te s t f a b r i c s Incorpora ted , NewJe r sey, U.S.A. and their. p e r t i n e n t phys ica l p r o p e r t i e s a re g ivenin Tables la and lb . The "warp" and "wef t" yarn p r o p e r t i e s ofnylon k n i t a re no t included in Table lb because th e "warp" and"wef t" yarns in k n i t s a re on e in th e same. The f a b r i c s werese lec ted mainly because they wicked a t r easonab le r a t e s and insuch quan t i t i e s t h a t the re was s u f f i c i e n t water to s h o r t c i r c u i tth e p ins and thus g ive a reading. Exper iments were done in bothth e warp and wef t d i r ec t i ons .

Table la . P e r t i n e n t Phys ica l Proper t i es of th e Fabr ics

Fib re Weave Yarn Thickness Mass Countmm (g/m 2 ) Yarns/cm

Nylon Knit double c f* 1.02 215 12x16knit

Wool Chal l i s p la in s t a p l e 0.46 124 22x28

Si lk pla in c f 0.15 60 42x34Broadcloth I

Si lk Noil pla in c f , 0.58 144 21x20s lubs 1

Linen pla in s t a p l e 0.20 89 22x18

Linen, Heavy pla in s t a p l e 0.38 223 14x15

Cotton, pla in s t a p l e 0.41 155 22x17Lightweight .. .

Cotton Duck pla in s t a p l e 0.58 328 21x17

* con t inuous f i lament

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Table lb . Pert inent Physical Propert ies of th e Fabrics Continued

Fabric % Water in % Water in Twist of 1 Twist ofDescript ion Warp Yarns Weft Yarns Warp Yarns Weft Yarns

_........... .....per 10 cm p er 10 cm

Wool Chall is 106 107 71 2-ply 4530

Silk 138 167 65 2-ply 55Broadcloth 31

Silk Noil 200 283 57 60

Linen 125 83 41 46

Linen Heavy 96 109 36 32

Cotton, 173 143 45 58Ligh twe igh t ....

Cotton Duck 159 193 46 2-ply 46 2-ply35 52

To confirm th e precision of th e experimental procedure, th ewater was coloured with red in k and several experiments were doneas described above while th e advance of th e water f ront wassimultaneously recorded and observed visual ly. The corre la t ionof th e two sets of data was extremely good.

In order to determine th e reproducib i l i ty of th e method, th eexperiments on several fabrics were carried out on fouroccasions. Typical r e su l t s are shown in Figure 2.

I . . . . .. . . . . . . . . . . . . . . . . . . . . . ... ..... . ......

Time

Figure 2. Typical Wicking Results

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The basic shape of th e wicking curves is th e same, only th eplacement on th e Y-axis d i ffe r s . This is considered to be due toth e var iab i l i ty in th e specimen's readiness to start to wick orth e "priming" fac tor. This var iab i l i ty is probably due to unevenf in ish ing of th e fabric. This r e su l t duplicates Holl ies r e su l t s(7) in which h is plots of distance versus th e square of time didnot pass through zero. Because of th e exce l len t reproducibi l i tyin our th e wicking e;tperiments when th e priming fac tor isel iminated, only one t e s t was done fo r each fabric.

Experimental Limitat ions

The experiment is limited by th e operating charac te r i s t i c sof th e apparatus. For instance, th e fabr ics were se lec tedbecause they held su ff i c i en t water to cause a short ci rcui tbetween th e common pin and each successive pin. With th eexception of th e nylon double kni t , th e fabrics which wereselected with t h i s character is t ic were made from natural f ibreswhich tend to have th icker yarns. Further, th e data acquis i t ionsystem was such t ha t only a f in i te number of readings could bemade during any experimental run. If th e fabric wicked veryquickly, many readings per un i t time were made and so th eexperiment would have to be terminated, say, a f t e r 100s. Thiscontrasted with experiments in which th e fabric wicked veryslowly, and were stopped a f t e r about 1500s. This was donebecause it was thought tha t evaporation of water from th e wickingsample would introduce an error into th e r e su l t s .

Experimental Results and Discussion

The experimental resul ts of th e ver t ica l and horizontalwicking for both th e warp and weft direc t ions are shown inFigures 3 through 10.

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Nylon KnitWarp Vertical

50 7- Warp Horizontal45 - Weft Vertical

40 {40_ -- Weft Horizontal

-- 3530

=0M 15 fS10

5

0

0 500 1000 1500 2000 2500 3000

Time (seconds)

Figure 3. The Wicking Behaviour of Nylon Knit

50 T Wool Challis

-540

350#

'~25-

= 20 % "20 I - Warp Vertical

- 7 -'-"--' Warp Horizontal100

/

0 "Weft Vertical5

- Weft Horizontal

0 I

0 400 800 1200 1600Time (seconds)

Figure 4. The Wicking Behaviour of Wool Chal l i s

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Silk Broadcloth45

40+

35

30

g 25

U 20 Warp vertical5- Warp Horizontal

---- Weft Vertical

1 Weft Horizontal

0 50 10 0 150 200 250 300

Time (seconds)Figure 5. Th e Wicking Behaviour of Si lk Broadcloth

Silk Noil50 -p

45 f-

40535- E

'' 25 u - ' - - - -~-Warp Vertical

20 4ii U---

20 r ' r*-- -- Warp Horizontal

1S t J "-4- Weft Vertical

1I ----.-- Weft Horizontal

0 50 100 150 200 250 300Time (seconds)

Figure 6. The Wicking Behaviour of Si lk Noil

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Linen25

20

SWeft vertical

0 Weft Horizontal

0 50 100 150 200 250 300

T~ime (seconds)

Figure 7. Th e Wicking Behtaviour of Linen

35 TLinen Heavy

~20

15__ _ _ _ _ _

S10 -a - Wwp Horizontal

> Weft Hoziwu

00 500 1000 1500

Time (seconds)Figure 8. Th e Wicking Behaviour of Linen Heavy

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Cotton Lightweight

35-/

30

25

20--o---- wtrp{lM1Wm

l0 t/ -O----- We f Honzmita

00 50 100 150 200 250

Time (seconds)

Figure 9. The Wicking Behaviour of Cotton Lightweight

Cotton Duck

40 . .:.

"-, I 7 ,S - --'Weft Horizontal

0 50 100 150 200 250

Time (seconds)

Figure 0. The Wicking Behaviour of Cotton Duck

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The graphs show t h a t th e major i ty of th e f a b r i c s wickeds imi l a r l y to t h e o r e t i c a l capillaries, with th e water movingqu ick ly along th e fabr ic and then s lowing up with t ime. Therewere some f a b r i c s fo r which th e wicking was a t a c o n s t a n t r a t e ,and with in the c o n s t r a i n t s of this experiment, wicking had noty e t s t a r t ed to slow with t ime. This mainly occurred in th eh o r i z o n t a l d i r e c t i on .

Table 3. summary of Wicking Resu l t s

Fabric Wicking Behaviour DistinctiveSDuring Experiment Ch arac t e r i s t i c

Nylon Kni t Hor izon ta l f a s t e r and Cross - sec t iona lS....farther . . .. t roughs

Si lk Hor izon ta l f a s t e r and 42x34 countBroadcloth f a r t he r 2-ply warp yarn

Linen,Heavy Ve r t i c a l f a s t e r and Nonehigher

Linen Warp f a s t e r and h igher More wate r in warpS...yarns

Wool Chal l i s Weft h o r i z o n t a l s lower 2-ply warp yarnsand shor te r

Cotton, Weft h o r i z o n t a l s lower Higher t w i s t weft...Lightweight .... yarns

Si lk Noil warp v e r t i c a l s lower More water in weftand lower yarns

Cotton Duck A ll s i m i l a r Higher t w i s t ply yarnsin weftMore -water in weft

The above Table shows t h a t this group of f a b r i c s d id notwick in a c o n s i s t e n t , s i m i l a r manner. When l i n e s of b e s t fit foreach curve was determined, only th e silk broadc lo th , weftve r t i c a l and th e nylon double k n i t , weft v e r t i c a l gave th ec l a s s i c s = ktI/2 equa t ion .

However, in a couple of ins tances , a unique physicalproper ty of a fabr ic can exp la in its wicking behaviour. Forins tance , th e nylon double k n i t wicked qu icke r h o r i z o n t a l l y thanve r t i c a l l y in both th e warp and wef t d i r e c t i ons . Examination ofthis double k n i t showed t h a t it has distinct pa ths o r t roughs onits sur face . Thus when it was in th e h o r i z o n t a l p o s i t i o n , th ewater ra n in these t roughs , as wel l as wicking along th e yarns .

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No exp lana t ion could be found fo r why th e silk broadc lo thwicked more quickly in th e h o r i z o n t a l than in th e ve r t i c a lp o s i t i o n . From its d i s t i n c t i v e cha rac t e r i s t i c s , one would havet hough t t h a t the re would have been a d i f f e r e n c e between th e warpan d wef t r a t he r than between v e r t i c a l and h o r i z o n t a l . Likewise,the heavy l inen had no d i s t i n c t i v e c h a r a c t e r i s t i c s which wouldi n d i c a t e why it wicked more qu ick ly in th e v e r t i c a l r a t he r thanth e h o r i z o n t a l d i r e c t i on .

An exp lana t ion can be given fo r the l igh twe igh t l inen whichwicked h i g h e r an d f a s t e r in th e warp than in th e wef t d i r e c t i o n .The warp yarns absorbed cons ide rab ly more wate r than th e weftyarns (103% versus 83%) . In th e exper iments wi th th e dy e and th ewoven f a b r i c s , it was observed t ha t the re were u s u a l l y two" f r o n t s " which moved up th e strip of f a b r i c . The first f r o n t wasth e wate r going up th e yarns which had one end immersed in th ebeaker of water and th e second f r o n t was th e wate r wicking f romthese yarns to and along the c ross yarns . Thus th e r a t e ofwicking depended on two f a c t o r s , th e r a t e a t which wate r wasdrawn up th e yarns which had their ends in th e water an d th e r a t ea t which water was "bled" o ff t h e s e yarns to fill t he c rossyarns . As a coro l la ry to latter s t a t ement , th e ra te of wicking upthe yarns depended on how much water had to be bled in to th ec ross yarns to fill them to capac i ty. Thus as th e water moved upth e l inen in th e wef t d i r e c t i o n , cons ide rab le amounts of waterwere bled o ff to fill up th e warp yarns , slowing th e wicking ratein th e wef t d i r e c t i o n .

No t suppor t ing th e above exp lana t ion are th e silk noi l andth e co t ton duck which should have wicked more qu ick ly in th e weftd i r e c t i o n s ince their wef t yarns held more water than th e warpyarns .

As d e t a i l e d in th e literature review, pl ied yarns and yarnsof in te rmedia te t w i s t should wick wate r h igher. This is notborne ou t by th e i n c o n s i s t e n t behaviour o f th e wool challis, th el i g h t w e i g h t cot ton and th e co t ton duck which have e i t h e r p l i edyarns or yarns o f distinctly d i f f e r i ng tw i s t s .

conc lus ion

Te x t i l e s f a b r i c s contain imper fec t capillaries, with no oneproper ty, o t h e r than gross sur face cha rac t e r i s t i c s such as th et roughs on the su r face of the double k n i t , un ive r s a l l yc o n t r i b u t i n g to their wicking behaviour. There fo re , th e wickingbehaviour of each fabr ic must be determined i n d i v i d u a l l y.

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Refe r e nces

1. R.M. Crow. M oi s tu re , L i q u i d s and Textiles. DREO R e p o r t 920,1987.

2. R.M. Crow and M.M. Dewar. Liquid t ranspor t Across FabricLayers. DREO Report 1002, 1989.

3. R.M. Crow and M.M. Dewar. The Movement of Liquid in Texti les .15th Commonwealth Defence Conference on Operational Clothing andCombat Equipment, Canada, 1989.

4. F.W. Minor, A.M. Schwartz, E.A. Wulkow and L.C. Buckles. TheMigration of Liquids in Texti le Assemblies, Par t II : The Wickingof Liquids in Yarns. Text. Res. J. 29, 12, pp 931-939, 1959.

5. N.R.S. Holl ies , M.M. Kaessinger and H. Bogarty. Water

Transport Mechanisms in Texti le Materials . Part I: The Role ofYarn Roughness in Capillary-Type Penetrat ion. Text Res. J ., 26,11, pp 829-835, 1957.

6. N.R.S. Holl ies , M.M. Kaessinger, B.S. Watson and H. Bogarty.Water Transport Mechanisms in Texti le Materials . Part II:Capillary-Type Penetrat ion in Yarns and Fabrics. Text Res. J.,27, 1, pp 8-13, 1957.

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UNCLASSIFIED-13-

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1. ORIGINATOR (the name and address of the organiaion preparg the document 2. SECURITY CLASSIFICATIONOrganieationS for whom the document was prepared. e.g. Establishment sponsoring (overall security classification of me documenta contractor's report, or tasking agency, ore entered in section 8.) including special warning terms if apphicl-te)

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Shir leys Bay, Ottawa, Ontario KIA OK23. TITLE Ithe complete document title as indicated on the title pame. Its classification should be indicated by the approprlite

abbreviation (S.C or U) in arentheses after the title.)

The Ver t i ca l and Horizonta l Wocking of Water in Fabr ics (U)

4. AUTHORS (Last name, first name, middle inital)

CROW, Rita M., DEWAR, Malcolm M.

5. DATE OF PUBLICATION (month and yer of publication of 6& NO. OF PAGES total 6b. NO. OF REFS Itota cited i,document) containing information. Include document)

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Department of National DefenceDefence Research Establ ishment Ottawa, Shir leys Bay, Ottawa, Ont. KlA OK2

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13. ABSTRACT ( a brief ani ta-ctua summary of the documenit .t a" also ppear e lsewhere n the body of h docuimnt ltsel. it is htighiydesirable that the abstract of classified documents be unclassified. Each paragraph of the absuact smliaJ egin with an ticnop of thesecurity classification 01 the information in the pragraph Iunless the document itself is unclassifld) represented as (S). (C), or (U)It is not necessary to include here asracts in beth offical ignugels uiless the text is bilingu.

This paper examines th e ve r t i c a l and hor izon ta l wickinnmovement of water alona a s t r ip of textile mate r i a l , a commonmethod of evaluat ing th e wicking behaviour of fabr ics . It wasfound t h a t th e fabr ics of t h i s study conta in imperfectcap i l l a r i e s , with no one proper ty, other than gross surfacecha rac t e r i s t i c s , universa l ly contr ibut ing to t h e i r wickinabehaviour. It was concluded tha t th e wickino behaviour of eachfabr ic must be determined ind iv idua l ly.

14. KEYWORDS. DESCRIPTORS or IDENTIFIERS (technica.ly meaningful terms or snort phrases than characterize a document and could behelpful in cataloguing the document They should be selected so that no security classification is reolired. Identifiers. Such as equipmenmmodel designation, trade nrae. military project code nane. geographic location may also be included. If possible keywords shmoid be selectedtrom a published thesaurus. e.g. Thesaurus of Engineering and Scientific Terms CTIST) and that thesaurus-identified. It it is not possible toselect indexing terms which are Unclassified, the classification of each should be indicated as with Me title.)

wickingcap i l l a ry water

fabr ics

UNCLAS S IF IED

SEURITY CLASSn CAtION OP FORM