Indi an Journal of Fihre & Textile Research Vol. 24. June 1999, pp. 86-92

Assessment of yam hairinessa

Arindam Basu

The South Indi a Textil e Research Association , P.B. No. 3205, Coimbatore Aerodrome P.O., Coimbatore 641 0 14, India

Received 15 April 1998; revised received and accepted 15 Jlln e 1998

The re lati onship between the different parameters used to express yarn hairiness by Shirley hairiness meter, Uster UT3 hairi ness tester and Zweig le G565 tester has been stud ied. It is observed that the Shirl ey hairiness values (hairs> 3 mm) show very good co rre lation (r = 0.98) with the results of Zweig le G565 tester when the same cri terion is conside red. Uster UT3 ha irincss results show medium correlation with Zweigle S3 values. An index has been developed from Zwei g le G565 rcsults which shows good corre lation (r = 0.94) with UT3 hairiness va lues.

Keywords: Hairiness index, Yarn hai riness

Introduction Thc yam s spun from fibres have protruding ends

and loops stand ing out of the core of the yams. These are commonly temled as hairs and the amount of hairs present per unit length is known as hairiness. Accordi ng to the nature of the fabrics and the characteri stics they must possess, the yam hairiness can ei ther be des irable or undesirable . For example, in some wi nter garments o r fa shion clothes the hairiness is desirable, whereas in garments worn adjacent to skin the hairi ness is most undesirable . For most of the end uses, too much ha iriness is undesirable . In high speed knitting and shuttleless weaving, the hairs cause breakages and lower the machine effic iency . Higher number of hairs on the surface o f the fa brics make the appearance fuzzy and are prone to pi ll forma tion .

To control hai riness one has to quanti fy the OCCUITences so that the e ffect of any measure undertaken can he understood proper ly. Depending on the instruments used to assess the ha iriness the unit of hai riness va ries. Sometime, thi s confuses people rather than he lp. In the present work, an attempt has been made to find out the relationship between different hairiness uni ts reported by Shirley hairiness meter, Uster UT3 hairiness tester and Zweigle G565 tester.

I . ! Factors Affecting Hairiness Vishwanathan ef C11. I reviewed the theoretical

explanations for the formation o f yam hairiness. Their

"Part of thi s work was p;'csented at the 39th joint technolog ica l confercnce of AT IR A. BTRA. SITR A & NITR A, New Delhi , 22-2.\ March 1998 .

study included fibre migration during the spll1ning process and the development of an opposing fo rce which acts outward as a result of elastic res istance due to twist pressure.

The influence of fib re properties has been studied by Barella and Manich2

. They observed that when yam parameters are di scarded, the multiple correlation coeffi cient between hairiness and fi bre parameters fa ll s apprec iably . The multiple regression equation leading to the minimum residual variance contains three variables, viz . fi bre length, uniformity ra tio and micronai re index for r ing-spun yams. Fibre length and its uniform ity rati o are the fa ctors exerting most in fl uence . Hi gher number of short fi bres cause more hai riness. Also, hairiness increases when the yam linear density increases. Recent stud ies by Zhu and Dean EthridgeJ show that the increasing fi bre strength, length and e longation reduce hairiness for both ring- and rotor-spun yam s. Their find ings are simil ar to those of Barella and Manich2 who observed that increasing fibre matu rity increases yam hairiness fo r both ring- and rotor-spun yams.

Spindle speed of ring spinning frame, ring traveller combination and twist per unit length are some of the major factors affecting yam hairiness. Yam hairiness increases with lower twist, higher spindle speed and roughness of ring and traveller surfaces . Higher winding speed increases the hairiness of the yams.

2 Materials and Methods

Fifty-eight yam samples , made o f 100% cotton and polyester/viscose (48/52 and 67/33) blends, o f varying count (Table I) were collected from various mills .

BASU : ASSESSMENT OF YARN HA IRINESS 87

2.1 1\1easuremen t of Ha iriness m IS reported. In the present versIOn of Shirley Yam hairiness was assessed by the following three hairiness meter, the testing of hair length can be

~ hairiness testers . varied up to 10 mm . The statistical analysis along

with other detai l of the results are reported by this 2.1 .1 Shirley Hairiness Meter latest version of instrument.

This instrument IS the most commonly used instrument for hairiness measurement. The older 2. 1.2 Uste r Teste r-3 Hairiness Meter Attachment version counts the number of hairs longer than 3 mm The hairi ness meter attached to the Uster Tester-3 (the projected length on an axis perpendicular to the was developed from the CRTM experiments4

. The yam axis) by photocell. The number of hairs per 1000 Centre de Researches Texti les de Mulhouse (CRTM)

Tab le I-Relationship between Uster hairiness and Zweigle G565 hai riness values

Sam- Yarn Zweigle resul ts (No. of hairs exceed ing) S3 K' Uster pie I mm 201m 3 mm 4 mm 6mm 8mm 10 mm 12mm H

o.

40C 19359 2990 630 11 3 2 0 0 0 745 3.92975 5.37 2 40C 141 75 2100 691 526 130 28 4 0 1379 3.2767 5.5 3 40C 24777 5325 19 16 976 125 25 3 0 3045 6.3197 5.91 4 40C 111 81 2080 544 240 35 5 I 0 825 2.53765 6.89 5 30CH 13242 '.833 466 256 59 18 2 0 80 1 2.79535 5.43 6 30CH 16252 2975 1200 1049 299 97 14 I 2660 4.4394 6.34 7 30CH 12228 1753 508 305 61 18 3 0 895 2.66495 5.19 8 30CH 13390 2309 671 348 60 17 I 0 1097 3.053 5.05 9 30CH 1356 1 2266 1023 1106 288 74 9 0 2500 3.7898 5.49 10 30CH 9461 1·129 202 61 7 I 0 0 27 1 1.8084 5.27 II 30CH 20358 4468 1917 1247 205 40 5 0 34 14 5.65015 6.74 12 .lOCH 20245 4347 1756 111 7 174 31 5 0 3083 5.45 18 6.73 13 .lOC H 21324 4729 2008 1379 246 59 I I 0 3703 6.01055 6.97 14 .lOCH 21925 4709 1953 1341 227 38 5 0 3564 6.01865 7.17 15 .lOCH 22729 527 1 211 8 1224 169 24 3 0 3538 6.2236 7.21 16 30CH 23345 52 15 2118 1224 169 24 3 0 3538 6.302 7.02 17 30CH 22930 5006 2168 1522 269 50 6 0 40 15 6.4507 7.25 18 30CH 21940 4730 19 11 1260 21 1 46 4 O' 3432 5.96585 6.97 19 30CH 21235 4544 1857 1166 185 28 4 0 3240 5.7133 6.99 20 :lOCH 21391 4483 1857 108 1 161 24 2 0 3125 5.65635 6.9 21 .lOCH 21268 4589 196 1 1278 20 1 39 3 0 3482 5.841 9 6.84 22 30CH 21226 47 11 2051 1317 204 39 4 0 36 15 5.9203 6.83 23 30CH 13555 2093 667 482 11 8 28 4 0 1299 3. 143 15 4.42 24 40CH 21723 4496 1756 1016 147 21 2 0 2942 5.62905 6.18 25 40CH 12332 1999 664 465 96 18 2 0 1245 2.90005 5.31 26 40CH 19756 4243 17 11 1019 165 29 3 0 2927 5.2774 6.26 27 40CH 10603 1532 388 194 34 10 0 0 626 2.23905 4.75 28 40CH 11238 1870 735 675 185 56 7 0 1658 2.93555 4.52 29 40CH 11985 2154 867 72 1 161 33 4 0 1786 3.1 47 5.33 30 2/60C 13207 2389 628 213 18 I 0 0 860 2.9181 5.26 31 44K 137i4 2478 1066 647 11 5 10 0 1839 3.4638 5.25 32 45CH 16408 3754 1647 11 89 215 43 5 0 3099 4.76535 5.03 33 2/ 100CG 23 12 268 82 33 I 0 0 0 116 0.4597 2.61

V 34 21l00CG 3138 419 11 9 38 5 I 0 0 163 0.6405 2.74 35 30PV 18258 35 11 1303 695 89 8 2 0 2097 4.49 17 6.44 .~(, 30PV 17403 .3.330 1238 70 1 77 6 0 0 2022 4.28605 6.48 Yi 30PV 17345 3587 1316 784 102 II I 0 22 14 4.4335 5.93 38 21()OPV 12302 1680 410 11 8 4 0 0 0 532 2.4706 5.82 39 80C 8405 1607 676 439 76 12 I 0 1204 2. 1837 3. 13 40 18C 31249 8235 3552 23 19 370 73 12 2 6328 9.4894 9.81 41 20K 28209 5876 2186 1266 179 32 2 I 3666 7.256 1 9.3 42 32C 18422 4258 1720 113 1 179 37 5 0 3072 5. 1594 7.44

(Collld)

88 IND IAN 1. FIBRE TEXT. RES., JUNE 1999

Table I-Relationship between Uster hairiness and Zweigle G565 hairiness values--Contd

Sam- Yarn Zweigle results (No. of hairs exceeding) S3 K' Uster pic I Illlll 2mm 3 mm 4mm 6mm 8 mm IDmm 12 mm H No.

43 2120K 2720.<) 50118 1356 435 21 I 0. 0. 1813 6.06 105 10.8 44 2132(' 22662 4822 1497 631 48 5 0 O· 2181 5.48235 9.4 45 27C 13250 5204 2017 124() 212 49 9 I 3534 6.3212 8.07 4() (jOC <)390 1669 555 323 53 9 0 0 940 2 .2267 3.3 47 (jOC 8337 1278 331 141 19 4 0 0 495 1.7733 3.24 48 (jOC <)3(j<) 15 70 549 299 54 10 0 0 912 2.1863 3.24 49 18K 27 140 6065 22 10 1195 172 25 4 0 3606 7. 10555 8.55 50 18K 29860 6393 2280 1288 163 27 3 0 3761 7.66095 8.62

.5 1 ()OC II 13445 2856 1243 763 128 21 5 0 2160 3.6613 4.44 52 IO()e 7842 1290 437 248 39 6 0 0. 730 1. 80845 3.38

5.' 9 1C 878 1 1474 528 331 42 9 I 0 911 2.07455 3.5 54 8K 11 450. 1972 742 437 73 14 0 1267 2.7535 3.98

55 82C I 1450 1972 742 437 73 14 0 1267 2.7535 4.36 )() 72C 13()25 2450 974 589 10 1 19 2 0. 1685 3.38165 4.41

57 2/30PV 17031 3145 863 327 28 2 0 0 1220 3. 82785 1.26 58 24C H 2 133 1 4260. 1497 769 94 17 3 0 2380 5.2575 7.69

Yarn : C H~Combcd cotton (Hosi ery): C~Co lllbed cotton ; CG~Colllbed cotton singed: K~Carded cotton: and PV- -PolyesterlV iscose. The number precedi ng Ihe words is ya rn coun t (Nel.

deve loped a prototype o f a new laser hairiness meter. Thi s appara tus \vas conceived ori gi nally from a model based on ya rn structure. According to this model, the ya rn is the resultant of a perturbation function that is essentia lly sllperfi c i::ll and a mass function of cohes ion that assures yam compac tness and corresponds to the diffe rence bet ween the core, which absorbs the laser light, and the superfic tal structure that diffracts this I ight. I n the laser i mage obta ined, the yam core appears black and the hairi ness red .

[n the hai riness tes ter unit attac hed with Uster TL'ster- 3. the mea suring fie ld is fo rmed by a homogeneou s field of paral lel li ght ( infra-red laser rays in thi s Il1 stance). If the ya rn lies in thi s measuring field. only those rays sca ttered by the fibres protruding from the main body of the ya rn reach the detector. Thi scattered I ight result s from the refrac tion. diffrac tion and the re fl ection at each of the separate tibres i.e. the protruding fib res seem to become luminous. Thi s sca ttered li gh t is a measure of hairiness and can be measured elec tr ica ll y. The direct ligh t. on the o ther hand. is absorbed by an aperture at the detec tor side . I I' no yarn is avai lab le In the measurtng fIeld. then no light fall s on the phutodetector. and therefore no e lectri ca ll y­measurahl e SIgnal is produced .

In the ha lliness meas uremen t unit , the ha irIness of approxIm atel y I em yarn length is cons idered. To ge t a heller understand In g of the calcul ated numeri ca l \·alue. the hairiness index (/-1) has been defined as the

tota l len gth of the protruding fibres w ith reference to the sensing length of I cm. This de fini t ion provides a basic meaning of the hairiness index H. As 'H ' is the relationship between two lengths (of hairs and yam), it is a non-dimensional entity.

2. 1.3 Zweigle G 565 Hairiness Tester

With thi s apparatus, the hairs up to 25 mm length (the projected length on an axis perPendicular to the ya rn axi s) emerging from a yam are counted by means of a series of photocells5

. The yam and projecting fi bres inten'upt a light beam, thus effectin g a fluctuation in the measurable luminance of the light beam. The luminance registered in thi s way by a phototransistor is converted into a photoc urrent w hich is amplifi ed . In order to allow the number of hairs in severa l length zones to be counted, the yam is scanned by four phototTansi stors .

In the earlier model s, only four chosen hair lengths cou ld be rec orded simultaneously, but in the latest ve rsion it is possible to obtain a frequency diagram of hairs protruding 1, 2,3, 4 , 6,8, 10, 12, \ 5, 18, 21 and 25 mm from the yam core. The apparatus al so gives, a t the end of the measurement , the number of hairs corresponding to each length interval and calculates as ha iriness index (H) . The results can be di splayed in the following two ways:

-Cumulat ive counting, e.g. the fibres of 3 mm length are regi stered and di splayed In the length zones of I mm , 2 mm and 3 mm .

. ..:

'I

BASU: ASSESSMENT OF YARN HAIRlNESS 89

-Differential counting, e.g. the fibres of 3 mm length are only registered in the length zone of 3 mm. Hairiness Index H is given by

H = IKix INi rRnl

where r= Regression coefficient

.. . (I)

Ki=Measuring distance (measured from the zero point)

Ni=Number of fi bres/ I 00 m in class R=Greatest calculable fibre length (point of

intersection of the region lines if y=0)

N smallest length m = - (of the selected classes)

N greatest length

This hairiness index is a non-dimensiomil numerical value, the quality of which provides a relative reference to the hairiness of the yarn.

This mdex is complex and the interpretation of this by user is very difficultu.

2.1.4 Comparison of Different Methods

For interpretation of any result one has to understand the testing principle of the instrument carefully. For the Shirley hairiness meter and Zweigle hai ri ness tester. the schematic diagram shown in Fig. 1 represents the measuring principles employed.

The number of hairs longer than H j is counted and ternled as , N j • For example, N) means the number of hairs exceeding 3 mm for a particular length of yam. Zweigle tester reports N J, N2, •. . ••• N25 per unit length of yam, where N I is the number of hairs in Class 1.. .. .. .... Class 12 i.e. exceeding 1-25 mm. In Shirley hairiness tester, the number of hairs exceeding a particula r length is counted .

In the case of Uster UT3 hairiness meter or Kelssoki Laserspot, the overall length of hairs per unit length is measured . This can be explained by Fig. 2.

H=l:. li per cm of yarn ... (2)

where Ii is the length of ith hair in cm. The Uster hairiness tester gives a figure that

defines the whole hairiness including the shortest hairs but does not give any infonnation about the distribution of hai r length whereas by Shirley or Zweigle hairiness testers the measurement can be done minimum 1 mm away from the surface i.e. the hairs smaller than I mm cannot be included. In . a yarn, the number of hairs that evolve near the yam core IS of some importance. On the contrary, if the

j ) ( /

Yarn Body

HI l ) ) \ I ~ H2 J ) \

I \ /

H3 7 ( \ Fig I- Hairiness by Zweig le G565 and Shirley hairiness testers

Yarn Body

Fig 2- Hairiness by Zellweger UT 3

hair length IS relatively short, the yam can appear very- hairy with UT3 and' only slightly hairy with Zweigle and Shirley hairiness testers.

Various researchers have attempted to find out the similarity in results obtained by various instruments. Barella el af.6 observed a correlation coefficient of 0.73 between the number of hairs protruding more than 3 mm from the yam core in both Zweigle G565 and Shirley devices . Agarwal7 observed a very good correlation between hairiness (S3) value given by Zweigle hairiness tester and Shirley hairiness meter (cumulative frequency of hairs having length 3 mm or more) in the count range of 7.5-30 tex. The correlation coefficient observed was 0.93 . From the principle of operation it is expected that there should be a good correlation between the results obtained by these two instruments.

Due to the difference in the principle of measurement by Uster UT3 hairiness tester as compared to Shirley or Zweigle hairiness tester, the conelation between the results is not so good. Coll-

Tortosa and Marcell08 compared the results of Zweigle tester and Uster Tester-3. A fair correlation (r = 0.78) was observed between some parameters

90 INDIAN 1. FIBRE TEXT. RES .. JUNE 1999

from the two exploration methods used by him for combed yams, but this was not good for carded yams (r = 0.46).

2.1.5 Testing Details The yams of different ongm and varying count

were tested for hairiness by Shirley hairiness meter, Zweigle G565 hairiness tester and Uster UT3 hairiness attachment. The testing speed, length and number of readings considered were as follows :

Shirley Hairiness Meter Test speed No. of readings per sample Testing time per reading

Zweigle G565 Hairiness Tester Test speed No. of readings per sample Testing time per reading

Uster TesterJ Hairiness Tester Test speed No. of readings per sample Testing time per reading

55 mlmin 10 2 min

50 mlmin 5 2 min

400 mlmin 5 2.5 min

All tests were carried out under standard atmospheric condition .

3 Results and Discussion

3. 1 Shirley Hair iness JlS Zweigle Hairiness The S3 value given by Zweigle G565 tester, i.e: the

number of hairs protruding more than 3 mm from yam surface, and the result of Shirley hairiness meter, i.e. the number of hairs more than 3 mm , were compared . The results are plotted in Fig. 3. It may be seen that though the actual values are not equal for these two testers, there is a very good correlation between these two values (r = 0.98). The Shirley hairiness values are higher than Zweigle S3 values. The difference in values may be due to the sensitivity of the photosensors used by the two different n anufacturers and the assumptions of yam surface for measurement of hairs . The regression equation is as follows:

S3=0.573 Ns+247.54 . . . (3 )

where S3 is the number of hairs longer than 3 nun by

Zweigle tester; and Ns, the number of hairs longer than 3 mm by SOL tester

80 r-----------------------~

I . , 'j I

I / I I

Me' 60, )( ,

E o o ~ 40 -.. en a: ~. ::z:: ..J c

. en 20

/ I /

' /

/. /

r = 0.98

0'"---'--'---'---'--'---'---'---· _ .L...-...J

o 5 10 1 5 20 25 30 35 40 45 50

ZWEIGLE S3/1000 m x 103

Fig 3- Correlation between hai riness by Shi,:ey and Zweigle hairiness testers

3.2 UT3 Hairiness vs Zweig Ie Hairiness As Uster UT3 measures the total length of hairs

and Zweigle G565 measures the number of hairs of different length group, a simple expression has been proposed to fi nd out the relationship between these two. Whi le developing this expression, the following two assumptions were made for simplic ity: - The average length of hairs lying between two

classes are the arithmetic mean value of those two class lengths .

- The protruding hairs are not in crimped condition. II

K = IN;' L; + N;2 ~ 2

;=1

h 1 + (/.1 ); were L =' ,..

, 2 1,= Length of hairs of class i "+I=Length of hairs of class (1+ I )

N,=Number of hairs in class i per 100 m

. .. (4)

If the K values are to be converted into the same unit as Uster II value, it has to be divided by 10,000 . K'=KIl 0,000 . . (:;) The K' values are gi ven in Table 1. It is observed that these values are lower as compared to J ster H vai ue. The relationship of Uster H value wltn 53, Zweig Ie index and K' values is shown in Table 2.

BASU: ASSESSMENT OF YARN HAIRINESS 91

The overall correlatio between Uster hairiness Index 1-1 and 1(' value from Zweigle hairiness has been found to be much higher as compared to the same with 53 and Zweigle index values (Figs 4-6)

When the hairiness of the yams from a particular orlgm with variable process Rarameters (20 tex combed cotton yams) IS compared, the correlation coeffIcient is found still higher (r=0.94) (Fig. 7). This show~ tha t both parameters.(Uster Hand Zweigle K') can be used with nearly equal accuracy to assess the efke' oi pr\l. c.,s r,arafl1elu, on hamnes~ In ti lls cas" a1St. j,L index l(' [w e pdge over Zwelgle 53 values:

,J de of the icas liS for having the lower values of , a: cC'mpared ' 0 Us(t;r if values may he (i) the '\d-'I()..;r and length of hairs smaller than 1 mm have

. ill)' lJeefl e()n~ idered. whIch should be much highel tti..,.C (. I ~>~ J t l ( ZweJ ~ie tester (i i) due to the crimp in ha ,. i: IS nos ih lt: or long haIrs to be regi stered iIi Sil'XI ~ ; len~lh gr~)Urs , hecause of the reduction i

., il. it-:> ..(' ~-C(.J lI ()~·' ot i~we !glc haifl'1css \ ulues and Ustc, l1 Jlflfl ~S~ Inde ):

_el::~_~~n t (,1 ___ f_i._R._i ___ __ 0_ .. _7_1 ___ ----.:0.-=.5...:.9 __

I

s.11 I

- I rn 5.11

-~

I

i 1.

1 . -; -i I

'. . !

r = 0.7.,

O. 1~1 ~~~ .• -~~-~~-~~--~~ 1 2 3 4 6 7 8 10 1 1

USTER H VALUE

r ig 4·-Corr,'i a!lon between Uster Hand Zwelgit: S3 vai ues

projected lengths of those hairs . This phenomenon has been confirmed in a study by Wang9

In which he has observed that the number of hairs in each classes

increase (specifically S3 value) with the Increase In

121

10 ~ I l //

W 8 f- //

3 i .;/. .. ~ I / . ' , J: 6 ~ . /. .

g r/ 4 ~ .. ,

! .' I.

2 ~ r = 0.59

1

/1

100 200 300 400 500 600 7 00

ZWEIGLE INDEX Fig 5- Corrclatlon between Uster H and ZwelgIc Index value,

10 " ------------------------~ +

+ + +

I 1 I

+"'t

r = 0.83 -I

+

+

2 4 6 8 10

USTER UT3 Fig 6-Correlation between Uster Hand Zweigle K' values

92 INDIAN J. FIBRE TEXT. RES., JUNE 1999

8~-----------------------~

) 6

+

+ /. 2 +

+Y :j:. +

+ +

r = 0.94

O L-----~------~-----~------~

4 5 6

USTER UTJ H

7 8

Fig 7-Correl ation between Uster 11 and Zweig1e K ' values for 20 tex combed cotton yams

testing speed. When the yams are tested at higher speeds, some of the crimped hairs get straightened due to air drag and are counted in higher length groups, (iii) the crimp formation by a fibre is related to its bending behaviour. When the yams made of same raw material were compared the trend of crimp formation remained nearly same (20 tex combed cotton yams) for different yams which may be the leason for having much higher corre lation behveen I<: values and Uster H values.

4 Conclusions There is a very good correlation behveen the

hairiness values reported by Shirley hairiness tester and Zweigle hairiness tester (r=0.98).

The correlation behveen the hairinesss value H given by UT3 and the number of protruding fibres longer than 3 mm given by Zweigle G565 is nGt very good (r=0.7).

The proposed measure derived from the results given by Zweigle G565 shows good correlation with the H value given by UT3 (r=O.83) .

Uster UT3, Zweigle G565 and Shirley hairiness testers can be used for assessing the effect of process parameters on yam hairiness with nearly equaJ accuracy. The proposed measure (I<: values) given by G565 has a high correlation with Uster H values (r=0.94) when the same raw material is used.

Acknowledgement The author is indebted to Ms. Indra Doraiswamy,

Director, SITRA, for continuous encouragement. He is thankful to Mr. T.V. Ratnam, Advisor, SITRA, for guidance in writing this paper.

References 1 Vishwanathan G, Munshi V G, Ukid ve A V & Chandran K,

Te.xt Res}, 59 ( II ) ( 1989) 707. 2 Barella A & Manich A M,} Text Inst , 79(2\ (J 988) 189. 3 Zhu R & Dean Ethridge M, Text Res J, 67(9 ) (1997) 694 . 4 ZeJlweger Uster A G, Measurement of yarn hairiness, TE

460 (Zellweger Uster AG, Switzerland), 1987. 5 Gerhand M, Wolfgang Topf, Me/liand Textdber, 66 (1 985)

245 . 6 Barella A, Egio A, Castro L & Manich A M, Text Res },

59( 11) (1989) 71 1. 7 Agarwal S K, Yarn hairiness and its variability , paper

presented at the 30th Joint technological conferenc:e of ATIRA, BTRA, SITRA and NITRA, Ahmedabad, 3-4 February 1989.

8 Coll-Tortosa L & Macello F X, Bollnlexler, 102(992) 5"/. 9 Wang X, } Textlnst, 88 (2) (J 997 ) 99.