Indian Journal of Fibre & Textile ResearchVol. 33, September 2008, pp. 223-229

Changes in dynamic drapability of polyester fabrics with weave density, yarn twistand yarn count obtained by regression equations

Mitsuo Matsudairaa

Department of Domestic Science, Faculty of Education, Kanazawa University, Kanazawa City, 920-1192 Japan

and

Sachiko Yamazaki & Yoshiteru HayashiIndustrial Technology Centcr of Fukui Prcfecture, Fukui City, 910-0 I 02 Japan

Somc ncw parameters of dynamic drapability, such as revolving drape increase coefficient (DJ, revolving drapecoefficicnt at 200 rpm (D200), and dynamic drapc coeflicient at swinging motion (Dd), have been defined using a device ofdynamic drape tester and the regression equations are derivcd fi'om mechanical parameters of fabrics obtained Ii'om KESsystcm. These equations have been applied to polyester fabrics used for women's fine dress materials and the effects ofweave dcnsity, yarn twist and yarn count on these parameters studied. It is observed that Dr and Dd have a maximum valueat the optimum weave density. These values increase with the increase in yarn twist in the case of Dechine" fabrics. Thesevalues decrease in the case of taffeta fabrics, and increase in the case of georgette with yam count. Changes in D200 withweave density, yarn twist and yarn count are found to be little for all the fabrics. ode number decreases and conventionalstatic drape coefficient (Ds) increases with weave density.

1 IntroductionDrapability of fabrics is very important especially

for women's fine dress materials because of itsrelation to beautiful appearance and/or elegantmovement of clothes. Draping behavior of fabrics instatic state has been studied and analyzed by manyscientistsl

-4; however, there have been few

investigations concerning dynamic drape behavior offabrics which are mostly related to beautifulappearance of clothes. Only a computer-based visionsystem developed by Stylios and Zhu5 is. reportedrecently.

Studies on drape behavior of fabrics have beenreported by Matsudaira et al.6

-1 t recently and much

progress has been achieved. It has been found thatthere exists an inherent node number for any fabric,and the conventional static drape coefficient (Ds) ofthe fabrics could be measured by image processing'system with high accuracy and reproducibility.6 Thenthe regression equation for the coefficient was derivedfor both isotropic and anisotropic fabrics7

, and theeffect of basic mechanical parameters of fabrics on

'To whom all the correspondence should be addressed.E-mail: matsudai@ed.kanazawa-u.ac.jp -

these static drape shapes was analyzed quantitativelyby computer simulation.s Further, dynamic drapebehavior of fabrics was examined u~ing a device ofdynamic drape tester. The revolving drape increasecoefficient (Dr) which means the spreading ratio ofoverhanging fabrics with revolution, and revolvingdrape coefficient at 200 rpm (D200)' which means thesaturated spreading of fabrics a"trapid revolution weredefined and their regression equations werederived.9.

lo Finally, dynamic drape coefficient atswinging motion (Dd), which is considered to be moresimilar to the human waist motion at walking, wasdefined and the regression equation was also derivedfrom the basic mechanical parameters of fabrics. I I

Then, these dynamic drape coefficients of polyesterfibre "Shingosen" fabrics and silk fabrics wereinvestigated widely and peculiar features of thesefabrics" became clear by these dynamic drapecoeffici~l)t's quite recently. 12-14 '

In tl1is paper, definitions of these dynamic drapecoefficIents have been explained and the effect ofweave density, yarn twist and yarn count on drapecoefficients of polyester fabrics investigatedusing the regression equations developed byMatsudaira et al.6-tI

2.1 SamplesPolyester samples were used for investigating. the

effects of weave density, yam twist and yam count onfabric drapability. The details of standard and normalsamples are shown in Table 1. These samples aretypical kinds of plain weaves made of polyester fibresand used mainly for women's fine dress fabrics inJapan now.

Taffeta is the most basic fabric consisted of twist-less continuous filament yams in both warp and weftdirections. Weft yam density was changed indecreasing and increasing directions from thestandard density which was decided empirically. Weftyam count was also changed to study the effect ofyam count.

Dechine consists of weft continuous filament yamswith high twist and twist-less or low twist warpcontinuous filament yams, having small crepes on thesurface. Weft yams with S-twist (left-handed twist)and Z-twist (right-handed twist) are used alternatelyby 2 yams (SZ2). Weft yam density and weft yamtwist were changed for investigation.

Georgette consists of high twist continuousfilament yams in both warp and weft, having smallcrepes on the surface. S-twist and Z-twist yams areused alternately by 2 yams (SZ2) for both warp andweft. Weft yam density and weft yam twist werechanged for Georgette-I, and weft yam count waschapged for GeOl'gette-2. Georgette-2 has smallerlevel of twist than Georgette-I.

Pongee is made of false twist continuous filamentyams for both warp and weft. The name Pongee isoriginally used for silk fine dress fabrics. Weft yamdensity was changed.

Yoryu consists of warp continuous filament yamswith high twist (SZ2) and weft continuous filamentyams with high twist of left-handed twist (S). Largecrepes are shown on the surface in warp direction.Weft yam density and weft yam twist were changed.

In order to avoid the effect of finishing conditions,these samples have been processed through the samestandard and minimum steps of finishing procedureused for polyester fabrics, such as relaxing andscouring, washing, drying, heat setting, and cooling.Dyeing and final finishing treatments were notexecuted.

2.2 Mechanical ParametersAll the samples, each of the size 20 cm x 20 cm,

were measured for their basic mechanical propertiesby KES (Kawabata Evaluation System for Fabrics)system under the conditions of 20°C and 65% relativehumidity. Three pieces were measured for eachsample and average value was used for analysis.

3 Results and Discussion3.1 Calculation of Drape Coefficients

3.1.1 Conventional Static Drape CoefficientStatic drape coefficient of fabrics (Ds) and node

number (n) are calculated using the followingequations 7

:

* B Gn = 12.797 - 269.93 - + 38060-- 2.67-

W W W

+13.03 ~2ZG ... (2)

Table I - Specifications of standard polyester fabric samples

Fabric Thread density/m Count, tex (filament) Twist, turns/m Thicknessa WeightWarps Wefts Warp Weft Warp Wefi mm g/m2

Taffeta 4370 3310* 8.3(36) 8.3(36)* 0 0 0.130 72.0

Dechine 5120 3540* 8.3(36) 8.3(36) 250(S) 2500(SZ2)* 0.193 89.2

Georgette-I 3980 3460* 8.3(36) 8.3(36) 2500(SZ2) 2500(SZ2)* 0.335 95.7

Pongee 4410 3500* 8.3(36) 8.3(36) 0** 0** 0.288 80. J

Yaryu 3190 3660* 8.3(36) 8.3(36) 2500(SZ2) 2750(S)* 0.300 84.1

Georgette-2 3740 3700 8.3(36) 8.3(36)* 1000(SZ2) 1000(SZ2) 0.171 72.7

*This' value was changed in both increasing and decreasing directions.**False-twisted textured yarn.aThickness is measured at the pressure of 49 Pa.

where Ro is the radius of circular supporting stand(63.5 mm); a, the constant showing total size of two-dimensionally projected area (mm); b, the constantshowing height of cosine wave of two-dimensionallyprojected shape (mm); and anu bill, the constantsshowing anisotropy of fabrics. These constants areobtained from the basic mechanical parametersmeasured by KES system using following equations7

:

a=35.981+1519 /13 -204300~Vw W

+23.27 JG +O.OI78G ... (3)VW2HG

b = 29.834-1.945n -0.0188G -91.84-- (4)W

Xa =9063(B1 -B2) 3

III WX

b = 6224( B, - B2) 3Ill, W

where B is the bending rigidity (mN' m2/m); G, theshearing rigidity (N/m/rad); 2HG , the hysteresis inshearing force at 0.0087 radian (N/m); W, the fabricweight (g/m2

); and B, & B2, the bending rigidity inwarp and weft directions respectively.

3./.2 Dynamic Drape CoefficientA device of dynamic drape tester is shown in

Fig. 1. This tester is composed of a circularsupporting stand having the same size with lIS(Japanese Industrial Standard) drape tester (127 mmin diameter) which can rotate from 0 rpm to 240 rpmcontinuously and also turn-round reversely at anarbitrary angle.9 Changes in drape coefficient ofseveral representative fabrics with the increase ofrevolution speed are shown in Fig. 2. It is clear thatthe difference of drape coefficient between fabricsbecomes distinct in the region between 50 rpm and130 rpm. Therefore, revolving drape increasecoefficient (Dr) is defined as the slope between drapecoefficient and rpm within this region. If thecoefficient is larger, the ratio of drape coefficientincrease with revolution speed is larger. Theregression equation for the coefficient is derived asfollows'o:

~2HG ~D. =0.792+2.374 -- -0.63053-I W W

a 2HG-6.7623 - - 2.673--+ 0.0005W

W W

5X)

80

;l.70.-e.

0: 60""E"0u"0-ro...0

--0- SanpleA

-,>;- SanpleB

----Sanple C

~SanvleD

-SanplcE

, On the other hand, if the revolution speed becomeslarger than 180 rpm, the drape coefficient does notincrease at all with the revolution speed. Therefore,revolving drape coefficient at 200 rpm (D200) isdefined as saturated drape coefficient at rapidrevolution. The regression equation for the coefficientis derived as follows1o:

GD200 = 61.475 - 37.02-+ 0.1411GW

~

2HB+40.883 - + 0.049W + 436.8--

W W

E-E" 0.4';f'.

~-.::..03E 0o~~o ~ 0.2

~~> •.•~ 0 0.1

•.• '" 900.0~~o E0. 80:;lj •..•:::g> N~ ~ 70

c:::::: ~

U UJt:•..oU

~ SOe.

•..~~ 0 00

2000 3000100 1

T,~etao ..::..OeOI'b'elte- I

~~i~pmb~O~'o Dxhine

-o-TaJleta-----X.-- r:h:::lline

--'-Y~I

SO 2~

.~ 40u

~0 30u•..g-O 20u0~ 10~0

02000 3000 4axJ 5000

The parameter Dd decreases with weave densitybasically; however, it seems that there exists anoptimum point where Dd shows the maximum value.In the case of Dechine and Taffeta fabrics, thosepoints may be at smaller region of the density. As Dd

means the degree of draping shape change of fabricsat swinging motion, every fabric has optimum weavedensity where the fabric is easy to change its drapingshape by small force such as light wind and/orswinging motion of human body.

3.2.2 Effect of Yam TwistNode number increases and Ds decreases with the

increase in weft yarn twist in the case of Dechinefabrics; however, they do not change at all in the caseof Georgette-l and Yoryu fabrics. These phenomenaare explained by the decrease in B with weft yarn

E0.

~ 0.4 ~I

YOlYLI• • •n A-C,eorgelte- I

/\ A

o"u 40E•..o

C;; 300.

r:ou 20

~o>, 10o

twist for Dechine fabrics. In the case of Goergette-land Yoryu fabrics, warp yarn has originally high twistas 2500 (822) and the effect of weft yarn twist has notbeen recognized.

The effect of weft yarn twist on Dr is shown inFig. 6. It is found that Dr increases in the shape of 8-letter for Dechine fabrics with the yarn twist;however, it does not change much for Georgette-l andYoryu fabrics. The effect of weft yarn density on D200

is found to be little for all the fabrics studied, i.e.Dechine, Georgette-l and Yoryu fabrics.

Results of Dd are shown in Fig. 6. The value of Dd

for Dechine fabrics il:creases with the yarn twist;however, it is saturated at more than 2000 turns/m.The values of Dd for Georgette-l and Yoryu fabricsdo not change at all because of original high twist ofwarp yarn.

3.2.3 Effect of Yarn COUlltNode number decreases and Ds increases largely

with the increase in weft yarn count in the case ofTaffeta fabrics; however, they do not change at all forGeorgette-2. This means that B increases with weftyarn count in the case of Taffeta fabrics; however, itdoes not increase in the case of Georgette-2.

"0--!:;t. 0.3

"<F- 0100

c

S 90"0- "0 0-

c3 80:;110

.~ f'I

~~~ 70

'" Ui-=

" GO0

GOOv

"<F-

50S~

.~ 40u

~0 -v"~ 2 -0

"~ \0-~0

00

I

5 \0,

~

rutCta

-"7

o 0

Geometrical structure of these Taffeta and Georgette-2 was observed and it was found that there was nospace between adjacent yarns in Taffeta fabrics;however, there was much space between them inGeOl"gette-2fabrics. Yarns are flat and wide in Taffetafabrics; however, yarns are thin because of twist inGeorgette-2 fabrics. Therefore, it is supposed thatthere is more space between warp and weft yarns atthe cross-over point and contacting force betweenthem is small for Georgette-2 fabrics. This is thereason why the effect of yarn count does not appearon B for Georgettc-2 fabrics and the effect of yarncount appears directly on B in the case of Taffetafabrics.

Dependency of Dr on weft yarn count is shown inFig. 7. The value for Taffeta fabrics decreases andthat for Georgette-2 increases with yarn count. Theeffect of yarn count might come out differently onshearing parameters, such as shear rigidity (G) andshear hysteresis (2EG) between Taffeta and

Georgette-2 because of the same reason as mentionedabove.

The effect of weft yarn count on D200 is shown inFig. 7. The value of D200 increases with the yarn countfor both Taffeta and Georgette-2 fabrics. This meansthat the saturated spreading of fabric at rapidrevolution increases with yarn count because of theincrease in fabric weight with yarn count.

Results of Dd are found to be similar to those of Dras shown in Fig.7. In the case of Taffeta fabrics, theincrease in Band G is much larger than the increase inW with yarn count, and brings about the decrease inDd. On the other hand, the changes in Band G arelittle and bring about the increase in Dd by theincrease in W for Georgette-2 fabrics.

4 Conclusions4.1 Node number decreases and conventional static

drape coefficient (Ds) increases with weave density.4.2 Revolving drape increase coefficient (Dr) and

dynamic drape coefficient at swinging motion (Dd)

might have the maximum value at the optimum weavedensity.

4.3 These values increase with yarn twist in the caseof Dechine fabrics; however, the effects are smallerfor Georgette and Yoryu fabrics.

4.4 These values decrease with yarn count in thecase of Taffeta fabrics; however, increase in the caseof Georgette fabrics.

4.5 Changes in revolving drape coefficient at 200rpm (D200) are found to be little with weave density,yarn twist and yarn count for all the fabrics studied.

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