Indian Journal of Fibre & Textile Research Vol. 3 1 , June 2006, pp. 279-285

Quality characteristics of polyester/viscose and polyester/cotton two-ply yarns

Arindam Basu" & Rajanna L Gotipamul The South India Texti le Research Association, Coimbatore 64 1 0 14, I ndia

Received 8 February 2005; revised received and accepted 26 April 2005

The i nter-relationship between the characteristics of single and double yarns made of polyester/viscose and polyester/cotton has been studied. The major yarn characteristics, such as unevenness, i mperfections, single yarn strength (RKm), strength CV%, elongation-at-break and yarn hairiness, of double yarns are found to be related to the respective properties of single yarns. The mass CV%, total imperfections, single yarn strength, elongation-at-break and hairiness of double and single yarns are highly correlated. Thick places and single yarn strength CV% show medium correlation.

Keywords: Elongation-at-break, Mass CV%, Neps, Polyester/cotton yarn, Polyester/viscose yarn, S ingle yarn, Yarn hairiness, Yarn imperfections

IPC Code: I nt. CI .8 D02G3/00, GO I N33/36

1 Introduction The production of folded yarns is expensive as

compared to single yarns of the same resultant count. Despite their additional cost, folded yarns are frequently produced because of the one or more benefits which may be obtained, e.g. reduced yarn i rregularity, increased yarn strength, reduced strength CV%, reduced yarn imperfections, production of novelty yarns, etc.

The expected improvement in the yarn properties of double yarns over the s ingle yarns has been reported by various researchers. 1 -4 Salhotra and Ghosh 1 have established a relationship in unevenness (CV%) and imperfections of single and plied yarns. Plying reduces both unevenness and imperfections and the amount of reduction is proportional to some power, say z, of the number of plies. The value of z i s about 0 .5 for CV%, 2 for thick places and neps, and 5 for thin places. According to Furter2, the CV% of plied yarns is given by the following relationship:

CVm(E) CV m(zn) = -_-, ­'< 11 . . . ( 1 )

where CV m(zll) i s the evenness of plied yarn; CV m(E), the evenness of single yarn; and 11, the number of single yarns in a ply yarn.

aTo whom all the correspondence should be addressed. E-mail : sitra@vsnl.com

Similarly, the imperfections are highly correlated.

Log Izn = log h - k . log 11 . . . (2)

where Izn i s the number of imperfections in a ply yarn; IE. the number of imperfections in a single yarn; and k, the constant (3 for thick places and neps and 4 for thin places).

As per Furter2, this equation can be applied for the prediction of thin places, thick places and neps separately.

The variation in tensile properties is given by the similar equation2 as used for CV% of mass, i .e.

CVRH(E) CV RH(zn) = _ , '< 11 (3)

where CV RH(zn) is the coefficient of variation of the tenacity of ply yarn consisting of 1 1 single yarns; and CV RH(E), the coefficient of variation of the tenacity of single yarn.

The hairiness (H) of ply yarn is given by the following relationship2 :

Hzn = HE + k. log 11 (4)

where Hzn is the hairiness of ply yarn; HE, the hairiness of single yarn; and k, the constant (the constant is 5) .

The p lied yarn tenacity is expected to be higher as compared to the single yarn tenacity. Plied yarn tenacity may surpass single yarn tenacity by as much as 30% (ref. 3) .

280 I NDIAN 1. FIBRE TEXT. RES., JUNE 2006

Though there is an i ncreased use of polyester/ cotton and polyester/viscose blended yarns, very few of the reported work is dealt with the blended yarns. A study has been conducted by SITRA to find out the relationship in various properties of double and single yarns.

2 Materials and Methods Twenty-two samples of the single (ring bobbins

and cones) and the double (cones) yarns, produced by different mi l ls , were used for the study.

These yarns were made of polyester/viscose (PN) and polyester/cotton (P/C) blended materials. The single yarn fineness ranged from 20s to 80s Ne and the PIC and PN blend proportion ranged from 48 :52 to 67 :33 . All yarns were spun by using ring spinning and for doubling either ring doubling or TFO was used.

The single and double yarns characteristics, such as unevenness (CY m%), imperfections, breaking strength, strength CY%, elongation-at-break and hairiness, were analyzed using the following methods and instruments:

Parameter Method Instrument

Count, count CV%, ASTM-D ( 1907-97) Electronic lea strength, and ASTM-D lea CSP strength CV% ( 1 578-93) tester

Irregularity and ASTM-D Uster tester 4 imperfections ( 1 425-96)

Hairiness by Uster Uster standards Uster tester 4 tester

S ingle yarn strength Uster standard method Uster and elongation traverse speed - Tensorapid 3

5000 mmlmin gauge length - 0.5m

Turns per unit ASTM-D SITRA length (twist) ( 1 422-99) microprocess

or twist tester

B lend analysis PIC, PlY (IS 34 16) Chemical method

3 Results and Discussion 3.1 Effect of Doubling on Yarn Unevenness

The unevenness in mass per unit length (CYm) of single yarn and the double yarn produced from the same single yarn is shown in Table I . The commonly used formula [(Eq. ( 1 ) ] has been used to calculate the

Table I-Mass CV% of s ingle and double yarns

Sample Mass CV % Deviation Deviation No. S ingle yarn Double yarn Predicted by Predicted by IX-XI I IX-X21

(X) SITRA Eq. (X I ) Furter Eq. (X2)

1 1 5 .37 1 1 . 1 3 1 1 .48 1 0.87 0.35 0.26 2 1 5 .92 1 1 .27 1 1 .77 1 1 .26 0.50 0.0 1 3 1 6.45 1 2.69 1 2.06 1 1 .63 0.63 1 .06 4 1 3 .05 1 0.28 1 0.23 9.23 0.05 1 .05 5 1 3 .00 1 0.28 1 0.20 9. 1 9 0.08 1 .09 6 1 5 .06 1 0.35 1 1 .3 1 1 0.65 0.96 0.30 7 1 5 .22 1 1 .28 1 1 .40 10.76 0. 1 2 0.52 8 1 3 .92 1 0.68 1 0.70 9.84 0.02 0.84 9 1 2.8 1 1 0.34 10 . 1 0 9.06 0.24 1 .28 1 0 1 3 .39 1 0.39 1 0.4 1 9.47 0.02 0.92 I I 1 3 .56 9.97 1 0.5 1 9.59 0.54 0.38 1 2 1 5 .45 1 1 .35 1 1 .52 1 0.93 0. 1 7 0.42 1 3 1 3 .49 1 0. 1 9 1 0.47 9.54 0.28 0.65 14 15 .47 1 2.05 1 1 .53 1 0.94 0.52 1 . 1 1 1 5 1 4.90 1 2.26 1 1 .23 1 0.54 1 .03 1 .72 1 6 1 3.92 1 1 .05 1 0.70 9.84 0.35 1 .2 1 1 7 1 4.99 1 1 .08 1 1 .27 10.60 0. 1 9 0.48 1 8 1 3 .89 1 1 .25 1 0.68 9.82 0.57 1 .43 1 9 1 8 .52 1 3 . 1 1 1 3 . 1 7 1 3 . 1 0 0.06 0.0 1 20 1 5.70 1 1 .73 1 1 .66 1 1 . 10 0.07 0.63 2 1 12 . 10 9.60 9.72 8.56 0. 1 2 1 .04 22 1 5 .50 1 1 .55 1 1 .55 10.96 0.00 0.59

Sum IX-XI i 6.87 Sum IX-X21 1 6.98

BASU & GOTIPAMUL: POLYESTER/VISCOSE & POLYESTER/COTION TWO-PLY YARNS 28 1

predicted CVm of double yarn. The actual and calculated values are shown in consecutive column. It can be observed from the table that the deviation between the actual and predicted values ranges from Nil to 1 .03 with the average of 0.3 1 and from 0.0 1 to 1 .72 with the average of 0.77 for SITRA and Furter equations respectively. The correlation between actual single yarn unevenness and actual double yarn unevenness is given below:

CVdm = 0.538 CVsm + 3.2 1 2

r2 = 0.766

. . . (5)

where CV dm is the mass CV of double yarn; and CVsm, the mass CV of single yarn .

The calculated values based on SITRA equation [(Eq. (5)] and Furter' s equation have been plotted against actual values (Fig. 1 ) . It can be seen that the SITRA equation gives much closer values.

3.2 Effect of Doubling on RKm CV %

When the RKm CV% of double yarn is compared with actual single yarn RKm CV%, the fol lowing equation emerges:

CVdr = 0.395 CVsr + 3 .66

r2 = OA01

. . . (6)

where CV dr is the R Km CV% of double yarn; and CV", the RKm CV% of s ingle yarn.

The difference between the calculated [Eq. (6)] and the actual double yarn RKm CV% ranges from 0.3% to 35. 13% (Table 2). Also, it can be seen from Eq . (6) that the correlation between double yarn RKm CV% and single yarn RKm CV% is good (r=0.63) but not as good as that with mass CV% (Fig. 2).

14 ,----------------------------, ... Actual 1 3 . -0- SITRA Eqn.

� 1 2 > u 1 1 (/) (/) ns

� 1 0

9 .

---- Furter Eqn.

3 5 7 9 1 1 1 3 1 5 1 7 1 9 21 Sample No.

Fig. I-Actual VS. calculated unevenness of double yarns

3.3 Effect of Doubling on RKm and Elongation of Yarn

The actual R Km and elongation-at-break values of single yarn and the double yarns produced from the same single yarn are shown in Table 3. It can be seen that there is an i ncrease in tenacity values for double yarn in all the cases and it ranges from 7% to 29%. It may be noticed that these yarns are commercially used yarns and optimum TM has been used. The i ncrease in elongation value ranges from 1 0% to 29%. When the single yarns are twisted during plying, the twist is applied in opposite direction to that of single yarns. This results in parallel ization of fibres and more fibres share the load when i t is applied on the yarn. This results in i ncreased yarn tenacity. The doubling twist also causes some shrinkage, resulting in increased yarn elongation-at-break. The correlation coefficient (r) for single and double yarns is of the order of 0.93 for RKm and 0.976 for elongation-at­break (Figs 3 and 4).

3.4 Effect of Doubling on Yarn Imperfections

The doubling or plying of yarn i nfluences the yarn i mperfections. For example, the thin places of s ingle yarn, which was identified due to its lower than -50% diameter, wil l become -25% after doubl ing. In that case, it wil l not be considered as thin places after doubling. Similarly, if a thick place comes beside a thin place during doubling the resultant yarn will not show any thick place. The actual imperfections, i .e. thi n places (-50%), thick places (+50%) and neps (+200%), of s ingle and double yarns are shown in Table 4.

1 3 ,------------------------------,

Rkm CV% (S ingle yarn)

Fig. 2-RKm CV% - single vs. double yarns

282 INDIAN J. FIBRE TEXT. RES. , JUNE 2006

Table 2-RKM CV% of single and double yarns

Sample � RKM CV% Deviation Deviation No. S ingle yarn Double yarn Predicted by Predicted by IX-XI I IX-X21

(X) SITRA Eq.(Xl ) Furter Eq.(X2)

1 2.56 7.84 8.62 1 1 .02 0.78 3 . 1 8 2 1 3 . 1 5 8.56 8.85 1 1 .54 0.29 2.98 3 1 4.35 1 1 .79 9.33 1 2 .59 2.46 0.80 4 9.2 6.53 7.29 8.07 0.76 1 .54 5 8.27 6. 1 8 6.93 7.25 0.75 1 .07 6 1 1 .28 7 .56 8 . 1 2 9.89 0.56 2.33 7 8.93 7.3 1 7 . 1 9 7 .83 0. 1 2 0.52 8 8.6 6.69 7.06 7.54 0.37 0.85 9 8.42 9. 1 8 6.99 7 .39 2. 1 9 1 .79 1 0 7.87 5 .82 6.77 6.90 0.95 1 .08 I I 8.49 6.84 7 .01 7.45 0. 1 7 0.6 1 1 2 1 0.32 6.95 7.74 9.05 0.79 2. 1 0 1 3 9.8 1 7 . 1 1 7.53 8.6 1 0.42 1 .50 14 1 1 .29 8.92 8 . 1 2 9.90 0.80 0.98 1 5 8.68 7.3 1 7.09 7.6 1 0.22 0.30 1 6 9.05 6.55 7 .23 7.94 0.68 1 .69 1 7 1 2.08 6.99 8.43 1 0.60 1 .44 3.6 1 1 8 1 0.3 1 8.77 7.73 9.04 1 .04 0.27 1 9 1 6.59 8.72 10.2 1 14 .55 1 .49 5.83 20 1 1 .69 9.54 8.28 1 0.25 1 .26 0.7 1 2 1 8.99 7.49 7.2 1 7.89 0.28 0.40 22 1 1 . 1 4 9. 1 8 8.06 9.77 1 . 1 2 0.59

Sum IX-X I I 1 8 .95

Sum IX-X21 34 .73

Table 3--1ncrease in RKM and elongation-at-break by doubling

Sample RKM, g/lex % I ncrease Elongation-at-break, % % Increase

No. S ingle yarn Double yarn S ingle yarn Double yarn

2 1 .4 1 24.95 1 6.53 7.45 9 .21 23.62 2 20.65 26.33 27. 5 1 7.70 9.93 28.96 3 1 9.85 24.74 24.63 7.62 9.56 25.46 4 22. 1 7 25.43 14.70 1 3 .86 1 5 . 1 8 9.52 5 24.73 28.02 1 3 .30 1 1 .97 1 3 .78 1 5 . 1 2 6 2 1 .09 27.06 28.3 1 1 1 .38 1 3 .39 1 7 .66 7 24.36 28.26 1 6.0 1 1 1 .80 1 3.23 1 2. 1 2 8 24.57 28. 14 1 4.53 1 0.87 1 2. 1 0 1 1 .32 9 25.68 27.2 i 5.96 1 3 .03 1 4.37 1 0.28 1 0 23.9 1 26.0 1 8.78 1 1 .22 1 2.69 1 3 . 1 0 I I 27.29 29.79 9. 1 6 1 1 .25 1 2.36 9.87 1 2 2 1 .35 24.68 1 5 .60 1 1 . 1 0 1 3.77 24.05 1 3 26.49 30.45 1 4.95 1 0.99 1 2.84 1 6.83 1 4 22.45 26.90 1 9.82 1 0.37 1 2. 1 2 1 6.88 1 5 22.78 24. 3 1 6.72 1 0.79 1 2.35 1 4.46 1 6 26.33 28. 5 1 8.28 9.82 1 1 . 1 8 1 3 .85 1 7 23.34 27.56 1 8 .08 1 2. 9 1 1 5 .2 1 1 7 .82 1 8 2 1 .26 23.38 9.97 10 . 1 3 12 . 1 6 20.04 1 9 1 8.45 23.82 29. 1 1 1 0. 1 0 1 2 .5 1 23.86 20 22.62 26.64 1 7 .77 8.52 1 0.82 27.00 2 1 1 0.93 1 2.08 1 0.52 5.98 7.49 25.25

BASU & GOTIPAMUL: POLYESTER/VISCOSE & POLYESTER/COTTON TWO-PLY YARNS 283

The correlation between these parameters have been workyd out and the following equations are found best fitting:

log (Thickd) =0.584 log (Thicks) -0.26 log (2) . . . (7)

r2 = 0.276

33 ,-------------------------�

C 31 � CI) 29 :0 ::J o e. 27 � :a, 25 E � . 0:: 23

•

•

y = O.9779x + 3.951 7 r = 0.93

• •

•

21 .�--�----_+----�----+_--� 1 8 20 22 24 26 28

RKm , g/tex (Single Yarn) Fig. 3--RKm - single vs. double yarns

log (Nepsd) =0.824 log (Nepss) -0.89 log (2) . . . (8)

r2 = 0.655

log (Impd) =0.852 log (Imp:) - l .24 log (2) . . . (9)

r2 = 0.6 1 3

1 6 �------------------------_.

"2 1 5 ... � 1 4 CI) :is 1 3 :l o 1 2 e. � 1 1

� 1 0 � m 9 . -'P 8

7 •

y = 0.9557x + 2.241 9 r = 0.976

c: o :z C1I CI c: o

6 +_----+-----+-----r---�----� W 5 7 9 1 1 1 3 1 5

8ongation-at-break, % (Single Yarn)

Fig. 4-Elongation-at-break - single vs. double yarns

Table 4-lmperfections of single and double yarns

Sample

No.

I 2 3 4 5 6 7 8 9 1 0 I I 1 2 1 3 1 4 I S 1 6 1 7 1 8 1 9 20 2 1

Thin places (-50%)

Single Double yarn yarn

2 1 86

3 1 8 I I 2 5

2 1 6 1 7 42 7 1 8 1 8 24 1 75 6 1 o 1 9

o 3 o o o o o o o I o o o o I o o 2 I o o

Thick places (+50%)

Single Double yarn yarn

1 2 1 1 66 27 30 34 37 1 7 7 3 72 26 35 63 10 2 1 28 35 1 24 50 23 25

9 26 8 2

I S 4 I 3 33 6 3 3 7 28 1 0 7 28 I I 2 5

Neps (+200)

Single Double yarn yarn

1 7 1 226 102 56 69 202 85 58 8 1

20 1 73 89 78 44 6 1 1 76 69

582 1 39 10 3 1

1 7 47 39 1 9 1 5 24 29 1 2 1 3 67 29 1 1 29 1 0 59 26 2 1 96 4 1 2 9

"Total No. of imperfections (-50%, +50%, +200%) of single yarn per 1 000m.

Single yarn - ring bobbin and Double yarn ---cone.

Total imperfections/km

Single Double SITRA yarn yarn Eq.(XI )"

3 1 3 478 1 30 89 1 2 1 250 1 04 70 85

275 1 1 5 1 4 1 1 83 6 1 1 00 222 1 28 8 8 1 250 33 75

26 76 47 2 1 1 6 39 33 1 3 1 6 1 0 1 35 1 4 32 1 7 88 36 28 1 26 53 4 14

56 8 1 27 20 5 1 47 22 1 6 1 9 5 1 24 28 36 1 4 2 1 43 26 1 35 47 8 1 7

284 I NDIAN 1 . FIBRE TEXT. RES., JUNE 2006

where Thickd is the number of thick places (+50%) of double yarn per 1 000 m; Thicks, the number of thick places (+50%) of single yarn per 1 000 m (ring bobbin) ; Nepsd' the number of neps (+200%) of double yarn per 1 000 m; Nepss. the number of neps (+200%) of single yarn per 1 000 m (ring bobbin) ; Impct, the total number of imperfections (-50%, +50%, +200%) of double yarn per 1 000 m; and Imps, the total number of imperfections (-50%, +50%, +200%) of single yarn per 1 000 m (ring bobbin).

The number of thin places of the double yarns becomes zero in most of cases . Hence, deriving any equation for that part of imperfections is not possible.

The prediction of individual imperfections, i .e. thin places, thick places and neps, of double yarns separately may not be useful as the correlation for thin places and thick places [(Eq. (7)] is not so good. However, the total imperfections of double yarn show better correlation (r=0.78) as compared to imper­fections of single yarn (Fig. 5) . The number of neps also shows good correlation (r =0.8 1 ) . The number of imperfections especially neps change after winding. The yarns are doubled using wound cones . Hence, the yarns fed to the plying process are not the ring yarns. These are coned yarns. An attempt has been made to find out whether the predictability of double yarn imperfections can be improved by using the number of imperfections of single yarn from cone.

Following regression equations have been evolved after analysis : log (Thickct)=0.655 log (thicksc) - 1 .0 1 log (2) . . . ( 1 0)

r2 = 0.373

log (Nepsct)=0.676 log (nepssc) - l . l 3 log (2) . . . ( 1 1 )

r2 = 0.53 1

log (Impct)=0.746 log (impsc) -0.86 log(2)

r2 = 0.568

. . . ( 1 2)

where Thicksc, is the number of thick places (+50%)/ 1000 m for coned single yarn; Nepssc, the number of

1 40 ,...--------------.

C 1 20 Y = 0.852·'og(lmps)-1 .24·'og2

� r = 0.783

� 1 00 · • ::l o • e. 80 E '" u; 60 c: .2 ti 40 � C1> Co

20 .E 0

0 200

'!t; 400 600 800

Imperfections/km (Single Yarn)

•

1 000

Fig. 5-Imperfections - single vs. double yarns

Table 5-Hairiness (H) of single and double yarns

Sample No.

2 3 4 5 6 7 8 9 1 0 I I 1 2 1 3 14 1 5

Single yarn

4.25 3.78 3.36 6.85 6. 1 2 7.03 5.95 6.52 5.85 5 .89 ·1.84 5.67 4.43 9.35 4.86

Hairiness (H) Double yarn Predicted by

( X ) SITRA Eq.(X l )

5 .87 5.75 4.68 5. 1 8 4.77 4.66 6.67 8.92 8.34 8.03 9.04 9. 1 4 7.56 7 .82 8.29 8.52 7.83 7.70 8 . 1 6 7.75 6.9 6.47 7.33 7.48 6.22 5.97 1 2.93 1 1 .97 7.24 6.49

Deviation Deviation Predicted by IX-XI I IX-X21

Furter Eq.(X2)

5.76 0. 1 2 0. 1 1 5.29 0.50 0.6 1 4.87 0. 1 1 0. 1 0 8.36 2.25 1 .69 7 .63 0.3 1 0.7 1 8 .54 0. 1 0 0.50 7.46 0.26 0. 1 0 8.03 0.23 0.26 7.36 0. 1 3 0.47 7.40 0.41 0.76 6.35 0.43 0.55 7. 1 8 0. 1 5 0. 1 5 5.94 0.25 0.28 1 0.86 0.96 2.07 6.37 0.75 0.87

Sum IX-X I I 6.97 Sum IX-X21 9.29

BASU & GOTIPAMUL: POL YESTERJVISCOSE & POL YESTERJCOTTON TWO-PLY YARNS 285

14

'2 1 2 "-(\I >- 1 0 QJ :c ::I 0 8 e. VI VI QJ 6 c: .;:: 'iij :I: 4

2 2 4

y = 1 .2 1 89x + 0.5687 . r = 0.928

•

6 8 Hairiness (Single Yarn)

1 0

Fig. 6--Best l ine fit - single yarn vs. double yarn hairiness

neps (+200%)11 000 m for coned single yarn; and Impse, the total number of imperfections/ l OOO m for coned single yarn.

These equations show that the consideration of single coned yarn parameters for prediction of imper­fections of double yarn does not improve the correlation. Hence, single yarn properties either from ring bobbin (i .e. thick places, neps and total imper­fection) or from cone yarns may be considered for the production of double yarn properties . In other words, the properties of double yarns are dependent on the quality of constituent single yarns.

3.5 Effect of Doubling on Yarn Hairiness

The hairiness of the double yarns is different from that of single yarns. The hairiness values of single and double yarns are shown in Table 5. Figure 6 and Table 5 show the influence of doubling on hairiness index (H). The hairiness (H) increases after doubling by 18 - 50% for 1 00% man-made and blended yarns used in the study. Before doubling, the ring yarn goes through single winding, doubler winding process but after doubling, it goes through either double yarn winding on another winding machine or winding part of two-for-one twister. It has been observed by various researchers that the winding process increases yarn hairiness as it is rubbed against various guides and drum. Two to three winding processes after spinning increase the yarn hairiness to a great extent. The doubling twist (being opposite in direction) neutralizes some of them. Also, the number of short hairs depends on the number of fibres per cross­section. Higher the number of fibres, more is the hairiness. The number of fibres becomes double after doubling, resulting in increase in final yarn hairiness.

4 Conclusions 4.1 The unevenness of plied polyester/cotton and polyester/viscose yarns is highly correlated with the unevenness of the constituent single yarns (r=0.875).

4.2 S ITRA equation predicts the mass CV% of double yarn from the mass CV% of single yarn more closer (average deviation of 0.3 1 ) to the actual values as compared to conventional equation by Furter (average deviation of 0.77).

4.3 The RKm CV% of double yarn is related to the RKm CV% of single yarn, but the correlation i s poorer (r = 0.634) as compared to that of mass CV%.

4.4 The tenacity of double polyester/cotton and polyester/viscose yarns improves by 7-29% as compared to that of single yarn . The increase in elongation i s to the extent of 1 0-29%.

4.3 There i s a good correlation (r) for RKm (0.93) and elongation (0.976) of single and double yarns.

4.6 The thick places, neps and total imperfections of double yarn is dependent on the thick places, neps and total imperfections of s ingle yarn respectively.

4.7 The hairiness (H) for single and double yarns shows excellent correlation (r=0.93). The H increases after doubling by 1 8-50%.

4.8 The s imilar correlation is observed for ring bobbin vs. double yarn and cleared cones vs. double yarn for all major yarn properties.

4.9 To produce good quality double yarn, one has to produce good quality of single yarn.

Acknowledgement The authors are thankful to the textile mills who

took part in S ITRA's recent inter-mill study of quality of man-made fibres and blended yarns used for this analysis. They are also thankful to Miss Indra Doraiswamy, Research Advisor, S ITRA, for her valuable suggestions during the preparation of the report. The services provided by the staff of Textile Physics Division are thankfully acknowledged.

References Salhotra K R & Ghosh N C, Relationship between imperfection count in single and ply yarns. Indian J Fibre Text Res, 1 2 ( 1987) 1 03.

2 Furter R, Evaluation of the quality characteristics of ply yarns. Asian Text J, April (2004) 42-44.

3 Lorenz R R C, Yarn twisting. Text Prog. 1 6 ( 1 /2) ( 1 987). 4 Coulson A F W & Dakin G, The influence of twist on the

strength and certain other properties of two-fold yarns, J Text Inst, 48 (7/8) ( 1 957) T207-T232.