-67-

Chapter 4

Influence of twist and blend ratio on characteristics of tencel-

polyester and tencel-cotton blended ring-spun yarns

4.1 Introduction

Tencel is amongst the strongest and stiffest regenerated cellulosic fibre ever

produced. It combines the advantages of both natural and synthetic fibres. It has the

softness of silk, the absorbency of cotton, and is fully biodegradable as well as highly

durable too. Its strength exceeds cotton and can even compete with a typical normal

polyester staple. Further, the strength is much less affected by wetting than other

made cellulosic fibres. Tencel‘s high strength leads to very strong yarns and fabrics,

and its high wet strength gives trouble free processing for both yarns and fabrics in

the wet state during sizing, dyeing and finishing of light weight fabrics. Besides, its

high modulus particularly in wet state, leads to very low shrinkage in water which

makes the garments truly launderable.

Tencel fibre also blends well with other natural or synthetic fibres such as

cotton, linen, polyester, lycra or wool, adding drape, comfort and performance to the

fabrics. The versatility of this fibre produces excellent fabrics for both men‘s and

women‘s casual and tailored wear, as well as lingerie in women, jersey and knitwear.

Although there are many papers, highlighting the advantage of tencel fibre [7-21,

111], only few reports have been published on the performance of tencel blended

yarns [51,112] and fabrics [113]. Kilic and Okur [51] investigated the structural,

physical and mechanical properties of cotton-tencel and cotton-promodal blended

ring, compact and vortex spun yarns and concluded that with increasing ratio of tencel

or promodal fibre content in the blend decreases unevenness, imperfection, diameter

and roughness value, but increases breaking force, elongation, density and shape

value. Kilic and Sular [112] studied the frictional properties of cotton-tencel yarns

produce on different spinning systems with different twist factors and test parameters.

They observed that yarn-to-yarn friction decreases, while yarn-to-metal and yarn-to

ceramic friction increase with the increasing ratio of tencel in the blended yarn for all

the input tensions. With the twist level, no systematic change is observed in yarn

frictional properties. Many researchers studied the influence of twist factor on the

characteristics of ring spun yarns [54, 55, 74, 76-88]. The present study, therefore,

-68-

aims at investigating the quality aspects of tencel-polyester and tencel-cotton ring-

yarns spun with different blend ratios and twist factors.

4.2 Experimental

Ring yarns of 29.5 tex were spun from tencel and its blend with polyester and

cotton fibres using different blend ratios and tex twist factor as discussed in Section

3.2.1 in Chapter 3. The fibre specifications of tencel, polyester and cotton fibres are

also mentioned in Table 3.1 in Chapter 3.

All the yarns were tested for single strand strength, breaking extension, yarn

irregularity, hairiness and flexural rigidity. The test procedures for all yarn properties

are given in Section 3.2.2 in Chapter 3.

4.3 Results and Discussion

The influence of three experimental factors, viz. fibre type, blend ratio and

twist factor, on the yarn characteristics was analysed for significance using ANOVA.

The significance of independent variables and their interactions on the yarn

characteristics were tested at a 99% confidence level i.e. probability level of 0.01. A

probability (p) value smaller than 0.01 leads to the conclusion that the independent

variable had a significant effect on the dependent variable. The results of the ANOVA

test are reported in Table 4.1.

The hypothesis to be tested in the study were determined as follow:

H0: No significant difference exists between average yarn properties.

The alternative hypothesis was as follows:

H1: Significant difference exists between average yarn properties.

If the F-ratio equals or exceeds the critical value, the null hypothesis (H0) is rejected.

It means if F-ratio is greater or equal to critical value than difference is statistically

significant and if it is less than critical value, than difference is said to be non-

significant. It is observed from Table 4.1 that main factors have strong influence on

most of the properties. The interaction effect of fibre type and blend ratio is

significant on all the properties. However, the interaction effect of blend ratio and

twist factor is mostly insignificant. Fibre type and twist factor interaction is

significant for tenacity and very short hairs only.

-69-

Table 4.1 − ANOVA test results

Process

variables

F–ratio

Tenacity Breaking

extension

Work of

rupture

Unevenness Imperfection Flexural

rigidity

Hairiness

Thin

places

Thick

places

Neps Total 1mm 2mm S3

A 528.11

(8.10)

4005.58

(8.10)

4281.2

(8.10)

1246.91

(8.10)

99.39

(8.10)

145.4

(8.10)

2239.6

(8.10)

1004.15

(8.10)

4.61

(8.10)

323.2

(8.10)

139.0

(8.10)

118.6

(8.10)

B 16.76

(4.43)

162.25

(4.43)

325.81

(4.43)

38.30

(4.43)

19.84

(4.43)

5.45

(4.43)

119.05

(4.43)

51.79

(4.43)

531.02

(4.43)

166.4

(4.43)

334.5

(4.43)

719.6

(4.43)

C 6.19

(4.10)

52.03

(4.10)

19.77

(4.10)

7.26

(4.10)

6.01

(4.10)

0.13

(4.10)

15.39

(4.10)

4.98

(4.10)

67.43

(4.10)

117.4

(4.10)

74.73

(4.10)

49.78

(4.10)

A*B 86.39

(4.43)

549.69

(4.43)

734.24

(4.43)

170.17

(4.43)

19.84

(4.43)

16.43

(4.43)

337.80

(4.43)

142.73

(4.43)

16.93

(4.43)

49.54

(4.43)

15.35

(4.43)

9.29

(4.43)

A*C 8.51

(4.10)

0.69

(4.10)

4.10

(4.10)

1.69

(4.10)

6.01

(4.10)

0.35

(4.10)

3.41

(4.10)

2.23

(4.10)

0.57

(4.10)

9.14

(4.10)

5.78

(4.10)

2.79

(4.10)

B*C 1.12

(2.94)

5.03

(2.94)

4.34

(2.94)

1.93

(2.94)

1.00

(2.94)

1.63

(2.94)

0.67

(2.94)

0.91

(2.94)

2.11

(2.94)

0.84

(2.94)

0.76

(2.94)

1.16

(2.94)

R2 .9811 .9972 .9977 .9908 .9442 .9306 .9952 .9892 .9923 .9892 ,9899 .9940

Figures in parentheses indicate critical value

A—Fibre type; B—Blend ratio; C—Tex twist factor

-70-

4.3.1 Tenacity

Table 4.2 shows the results of the tensile test. The results show that there are

marked differences between the yarns spun with different twist factors. For tencel-

polyester yarns, increasing tex twist factor from 23.93 to 33.50 leads to an increase in

tenacity which later drops with further increase in twist factor to 47.85 (Fig. 4.1). The

initial increase in yarn tenacity with increase in twist factor is attributed to the effect

of improved fibre cohesion which outweighs the effect of obliquity, however, a

further increase in cohesion due to twist is leveled off by the decrease due to well

known obliquity effect. Further, yarn tenacity increases as the tencel content in the

mix increases (Fig. 4.2) and the effect is significant for tencel-cotton mix too.

In case of tencel-cotton blends, the yarns exhibit highest tenacity when spun at

a twist factor of 38.28. This shift of optimum twist factor can be attributed to the

presence of short fibres in cotton. The optimum twist factor for 100% polyester and

tencel yarns are 33.5 and 28.71 respectively. The tencel-polyester yarns shows an

optimum twist factor at 33.50 i.e. equivalent to 100% polyester yarn when proportion

of polyester is 50% or more, whereas it is at 28.71 which is equivalent to 100% tencel

yarn when tencel proportion predominates irrespective of blend ratio used. The

optimum twist factor for 100% cotton yarn is at 43.07. The tencel-cotton blended

yarns shows optimum twist factor at 38.28, which is in between their respective

optimum twist factors.

-71-

Table 4.2 − Influence of blend ratio and twist factor on tenacity of tencel-polyester

and tencel-cotton ring- spun yarn

Fibre

type

Blend

ratio

Tenacity, cN/tex

23.93a 28.71

a 33.50

a 38.28

a 43.07

a 47.85

a

Tencel:

Polyester

0:100 35.1 35.3 35.4 34.6 33.8 30.5

25:75 28.1 28.7 29.9 28.5 27.5 27.2

50:50 26.1 26.7 26.8 26.0 24.0 22.4

75:25 23.9 25.4 23.9 23.3 22.6 21.5

100:0 22.4 23.4 23.3 22.0 20.7 19.3

Tencel:

Cotton

0:100 10.5 14.9 17.7 18.2 18.9 18.9

25:75 12.9 16.5 18.8 20.5 19.5 19.1

50:50 15.3 18.6 19.7 20.7 20.2 19.5

75:25 18.5 20.5 21.0 20.8 19.5 20.2

100:0 22.4 23.4 23.3 22.0 20.7 19.3

a Tex twist factor

-72-

Fig. 4.1 − Variation in tenacity with tex twist factor of tencel blended ring spun yarns

[(a) Tencel-polyester, and (b) Tencel-cotton]

0

10

20

30

40

50

0:100 TEN/PET 25:75 TEN/PET 50:50 TEN/PET

75:25 TEN/PET 100:0 TEN/PET

0

10

20

30

40

50

23.93 28.71 33.50 38.28 43.07 47.85

0:100 TEN/COT 25:75 TEN/COT 50:50 TEN/C0T

75:25 TEN/COT 100:0 TEN/COT

Tex twist factor

Ten

acit

y,

cN/t

ex

-73-

Fig. 4.2 − Variation in tenacity with blend ratio of tencel blended ring yarns spun at

different twist factors [(a) Tencel-polyester, and (b) Tencel-cotton]

10

15

20

25

30

35

4023.93 TF 28.71 TF 33.50 TF

38.28 TF 43.07 TF 47.85 TF

10

15

20

25

30

35

40

0 25 50 75 100

23.93 TF 28.71 TF 33.50 TF

38.28 TF 43.07 TF 47.85 TF

Tencel in blend, %

Ten

acit

y,

cN/t

ex

-74-

4.3.2 Breaking Extension

As expected, the tencel-polyester yarns exhibit higher breaking extension than

their tencel-cotton counterparts due to higher breaking extension of polyester fibre

(Table 4.3). The maximum breaking extension of 100% polyester, 100% cotton and

100% tencel yarns are found to be at twist factor of 47.85. The blended yarns also

show their maximum breaking extension at the highest twist factor i.e. 47.85. For all

fibre-mix, the breaking extension increases with the increase in twist factor (Fig. 4.3).

As more twist is inserted, the constituent fibre follows close spiral path within the

yarn. When such yarns are stretched, the spiral extends initially in place of the fibres

extension. This causes increased extension of the yarn with increase in twist factor. In

the case of tencel-polyester yarns, the breaking extension increases with the increase

in polyester content. Similarly, for tencel-cotton yarns, the breaking extension

increases with the addition of tencel fibre in the mix (Fig. 4.4). For both the fibre mix,

the yarn breaking extension is dominated by the presence of more extensible fibre.

-75-

Table 4.3 − Influence of blend ratio and twist factor on breaking extension of tencel-

polyester and tencel-cotton ring-spun yarn

Fibre

type

Blend

ratio

Breaking extension, %

23.93a 28.71

a 33.50

a 38.28

a 43.07

a 47.85

a

Tencel:

Polyester

0:100 12.00 12.73 13.08 13.51 14.59 14.88

25:75 9.90 10.34 11.08 11.24 11.64 12.25

50:50 8.84 9.27 9.64 9.78 9.79 9.68

75:25 7.96 8.30 8.48 8.36 8.59 8.67

100:0 7.16 7.22 7.25 7.29 7.27 7.46

Tencel:

Cotton

0:100 4.03 4.79 5.29 5.78 6.05 6.13

25:75 4.20 5.33 5.65 6.35 5.96 6.33

50:50 5.09 5.62 6.22 6.25 6.51 6.52

75:25 5.76 6.19 6.34 6.56 6.63 7.35

100:0 7.16 7.22 7.59 7.29 7.27 7.46

a Tex twist factor

-76-

Fig. 4.3 − Variation in breaking extension with tex twist factor of tencel blended ring

spun yarns [(a) Tencel-polyester, and (b) Tencel-cotton]

0

4

8

12

16

20

0:100 TEN/PET 25:75 TEN/PET 50:50 TEN/PET

75:25 TEN/PET 100:0 TEN/PET

0

4

8

12

16

20

23.93 28.71 33.50 38.28 43.07 47.85

0:100 TEN/COT 25:75 TEN/COT 50:50 TEN/C0T

75:25 TEN/COT 100:0 TEN/COT

Tex twist factor

Bre

akin

g e

xte

nsi

on

, %

-77-

Fig. 4.4 − Variation in breaking extension with blend ratio of tencel blended ring

yarns spun at different twist factors [(a) Tencel-polyester, and (b) Tencel-cotton]

4

6

8

10

12

14

16

23.93 TF 28.71 TF

33.50 TF 38.28 TF

43.07 TF 47.85 TF

4

6

8

10

12

14

16

0 25 50 75 100

23.93 TF 28.71 TF

33.50 TF 38.28 TF

43.07 TF 47.85 TF

Tencel in blend, %

Bre

akin

g e

xte

nsi

on

, %

-78-

4.3.3 Work of Rupture

It is evident (Table 4.4) that tencel-polyester fibre mix yarns have higher work

of rupture than tencel-cotton mix yarns (Fig. 4.5). In regards to tencel content, work

of rupture reflects a similar trend as yarn tenacity and breaking extension. The work

of rupture for tencel-polyester blended yarns is maximizes at around 33.5 tex twist

factor and the same is at 38.28 tex twist factor for tencel-cotton blended yarn. These

are intermediate values of twist factor that maximizes work of rupture for 100 %

tencel, polyester and cotton yarn. The data indicate a sizeable increase in work of

rupture with increased twist factor up to certain level (Fig. 4.6). Further increase in

twist factor beyond that level, however, lowers the work of rupture. The same

comment could be made on the decisive effect of higher twist factor.

Table 4.4 − Influence of blend ratio and twist factor on work of rupture of tencel-

polyester and tencel-cotton ring-spun yarns

Fibre

type

Blend

ratio

Work of rupture x 10-3

, g/den

23.93a 28.71

a 33.50

a 38.28

a 43.07

a 47.85

a

Tencel:

Polyester

0:100 239.9 256.4 262.6 264.9 279.6 257.2

25:75 157.6 167.9 187.8 181.5 181.6 188.6

50:50 130.8 140.9 145.8 143.9 133.3 122.7

75:25 107.8 119.3 114.6 110.4 110.1 105.7

100:0 90.8 95.8 100.0 90.7 85.3 81.5

Tencel:

Cotton

0:100 24.0 40.5 53.0 59.6 64.8 65.6

25:75 30.6 52.9 60.0 73.7 66.0 66.5

50:50 44.2 59.2 69.3 73.2 74.4 71.9

75:25 60.2 71.9 75.4 77.4 73.3 83.9

100:0 90.8 95.8 100.0 90.7 85.3 81.5

a Tex twist factor

-79-

Fig. 4.5 − Variation in work of rupture with blend ratio of tencel blended ring yarns

spun at different twist factors [(a) Tencel-polyester, and (b) Tencel-cotton]

0

50

100

150

200

250

30023.93 TF 28.71 TF33.50 TF 38.28 TF43.07 TF 47.85 TF

0

50

100

150

200

250

300

0 25 50 75 100

23.93 TF 28.71 TF

33.50 TF 38.28 TF

43.07 TF 47.85 TF

Tencel in blend, %

Work

of

ruptu

re x

10

-3, g/d

en

-80-

Fig. 4.6 − Variation in work of rupture with tex twist factor of tencel blended ring

spun yarns [(a) Tencel-polyester, and (b) Tencel-cotton]

0

70

140

210

280

350

0:100 TEN/PET 25:75 TEN/PET 50:50 TEN/PET

75:25 TEN/PET 100:0 TEN/PET

0

70

140

210

280

350

23.93 28.71 33.50 38.28 43.07 47.85

0:100 TEN/COT 25:75 TEN/COT 50:50 TEN/C0T

75:25 TEN/COT 100:0 TEN/COT

Tex twist factor

Work

of

ruptu

re x

10

-3, g/d

en

-81-

4.3.4 Mass Irregularity

Yarn irregularity (U %) of tencel-polyester and tencel-cotton yarns vary from

8% to 11.5% and 10.1% to 15.3% respectively (Table 4.5). As expected, evenness is

least for 100% cotton yarns, which improves with the inclusion of tencel fibre in the

fibre-mix (Fig. 4.7). Yarn evenness also significantly improves with increase in

polyester fibre content in the tencel-polyester mix. This improvement in yarn

evenness, however, depends on the twist factor used. For all yarns except 100%

cotton, evenness deteriorates as the twist factor is increased (Fig. 4.8). With the

increase in twist factor, the drafting speed reduces as increase of twist is accomplished

by reducing front roller delivery. The decrease in drafting speed decreases dynamic

friction between the fibres which controls the nature of movement of fibres in drafting

field. The movement of floating fibres become more regular when frictional restrain

to sudden acceleration increases. A reduction in drafting speed exercises lesser control

on fibre movement due to decrease in dynamic friction between the fibres. Hence, a

decline in evenness is observed when twist factor is increased. Surprisingly, however,

evenness continuously improves with the increase in twist factor in 100 % cotton

yarn.

-82-

Table 4.5 − Influence of blend ratio and twist factor on work of rupture of tencel-

polyester and tencel-cotton ring-spun yarns

Fibre

type

Blend

ratio

Unevenness, U%

23.93a 28.71

a 33.50

a 38.28

a 43.07

a 47.85

a

Tencel:

Polyester

0:100 8.78 8.95 9.04 9.17 9.19 9.23

25:75 8.87 8.95 9.16 9.26 9.26 9.46

50:50 9.30 9.27 9.45 9.54 9.51 9.64

75:25 9.37 9.59 10.19 10.22 10.30 10.51

100:0 10.13 10.51 10.65 10.87 11.23 11.52

Tencel:

Cotton

0:100 15.30 15.17 14.57 14.43 14.12 14.14

25:75 12.44 12.29 11.87 11.81 13.07 13.20

50:50 11.66 11.59 11.40 11.70 12.06 12.36

75:25 11.05 11.35 11.42 11.56 11.72 11.68

100:0 10.13 10.51 10.65 10.87 11.23 11.52

a Tex twist factor

-83-

Fig. 4.7 − Variation in unevenness with blend ratio of tencel blended ring yarns spun

at different twist factors [(a) Tencel-polyester, and (b) Tencel-cotton]

8

9

10

11

12

13

14

15

16

17

23.93 TF 28.71 TF 33.50 TF

38.28 TF 43.07 TF 47.85 TF

8

9

10

11

12

13

14

15

16

17

0 25 50 75 100

23.93 TF 28.71 TF 33.50 TF

38.28 TF 43.07 TF 47.85 TF

Tencel in blend, %

(a)

(b)

Unev

ennes

s, U

%

(b)

-84-

Fig. 4.8 − Variation in unevenness with tex twist factor of tencel blended ring spun

yarns [(a) Tencel-polyester, and (b) Tencel-cotton]

0

4

8

12

16

20

0:100 TEN/PET 25:75 TEN/PET 50:50 TEN/PET

75:25 TEN/PET 100:0 TEN/PET

0

4

8

12

16

20

23.93 28.71 33.50 38.28 43.07 47.85

0:100 TEN/COT 25:75 TEN/COT 50:50 TEN/C0T

75:25 TEN/COT 100:0 TEN/COTUnev

ennes

s, U

%

Tex twist factor

-85-

4.3.5 Imperfections

As can be observed form Table 4.6, the frequency of imperfections in the

tencel-polyester yarns increases with increase in tencel content in the mix (Fig 4.9). In

the case of tencel-cotton yarns, an increase in proportion of tencel fibre in the mix

leads to a marked reduction in imperfection indices on account of increase in the

proportion of long fibres in the mix, which allows better control of fibre movement

during drafting. In regards to twist factor, the yarn imperfections (Fig 4.10),

particularly neps and thin places, show a continuous increase with the increase in

twist factor. This is in agreement with the observation by Simpson and Fiori [55]. The

increase in dynamic friction between fibres in the drafting field, as stated above, with

decrease in twist is responsible for improvement in uniformity and imperfections.

-86

-

Table 4.6 − Influence of blend ratio and twist factor on imperfection of tencel-polyester and tencel-cotton ring-spun yarns

Fibre

type

Blend

ratio

Thin places/ km Thick places/ km Neps/ km Imperfections/ km

23.93a 28.71a 33.50a 38.28a 43.07a 47.85a 23.93a 28.71a 33.50a 38.28a 43.07a 47.85a 23.93a 28.71a 33.50a 38.28a 43.07a 47.85a 23.93a 28.71a 33.50a 38.28a 43.07a 47.85a

Tencel:

Polyester

0:100 0 0 0 0 0 0 1 0 0 1 0 2 2 4 4 6 6 8 3 4 4 7 6 10

25:75 0 0 0 0 0 0 4 0 4 2 0 4 8 12 12 24 20 24 12 12 16 26 20 28

50:50 0 0 0 0 0 0 16 8 6 4 0 4 32 32 40 40 52 56 48 40 46 44 52 60

75:25 0 0 0 0 0 0 12 10 8 8 6 4 48 64 68 76 72 76 60 74 76 84 78 80

100:0 0 0 0 0 0 0 30 28 20 12 14 12 56 52 56 52 80 92 86 80 76 64 94 104

Tencel:

Cotton

0:100 6 8 10 18 24 26 48 60 76 80 100 128 276 304 328 328 356 396 330 372 414 426 480 550

25:75 4 6 8 10 12 18 36 32 48 56 68 76 236 252 236 252 268 284 276 290 292 318 348 378

50:50 0 2 4 4 6 12 56 44 42 40 22 24 156 148 172 184 192 192 212 194 218 228 220 228

75:25 0 0 2 0 4 4 56 64 48 36 32 16 104 128 108 128 132 176 160 192 158 164 168 196

100:0 0 0 0 0 0 0 30 28 20 12 14 12 56 52 56 52 80 92 86 80 76 64 94 104

a Tex twist factor

-87-

Fig. 4.9 − Variation in imperfection with blend ratio of tencel blended ring yarns spun

at different twist factors [(a) Tencel-polyester, and (b) Tencel-cotton]

0

100

200

300

400

500

60023.93 TF 28.71 TF

33.50 TF 38.28 TF

43.07 TF 47.85 TF

0

100

200

300

400

500

600

0 25 50 75 100

23.93 TF 28.71 TF

33.50 TF 38.28 TF

43.07 TF 47.85 TF

Tencel in blend, %

Imper

fect

ion/k

m

-88-

Fig. 4.10 − Variation in imperfection with tex twist factor of tencel blended ring spun

yarns [(a) Tencel-polyester, and (b) Tencel-cotton]

0

150

300

450

600

750

0:100 TEN/PET 25:75 TEN/PET 50:50 TEN/PET

75:25 TEN/PET 100:0 TEN/PET

0

150

300

450

600

750

23.93 28.71 33.50 38.28 43.07 47.85

0:100 TEN/COT 25:75 TEN/COT 50:50 TEN/C0T

75:25 TEN/COT 100:0 TEN/COT

Tex twist factor

Imper

fect

ions/

km

-89-

4.3.6 Flexural Rigidity

Among 100% tencel, polyester and cotton yarns, the former shows highest

flexural rigidity followed by polyester and the cotton yarns (Table 4.7). The yarns

follow the order in which tensile modulus and linear density of individual fibres exist.

The flexural rigidity of tencel fibre is highest due to being coarsest and having higher

individual modulus. The tencel yarn therefore shows highest flexural rigidity too (Fig

4.11). The same argument can be extended to 100% polyester and cotton yarns. The

blended yarns show flexural rigidity values which are in between their 100%

constituent yarns. Furthermore, the flexural rigidity of all the yarns shows an

ascending trend with the increase in twist factor (Fig 4.12). The expected increase in

yarn compactness due to increase in inter fibre cohesion could impair the freedom of

fibre movement and hence a high flexural rigidity.

Table 4.7 − Influence of blend ratio and twist factor on flexural rigidity of tencel-

polyester and tencel-cotton ring-spun yarns

Fibre

type

Blend

ratio

Flexural rigidity x 10-3

, g.cm2

23.93a 28.71

a 33.50

a 38.28

a 43.07

a 47.85

a

Tencel:

Polyester

0:100 2.30 2.87 2.87 3.11 3.15 3.22

25:75 3.01 3.03 3.23 3.33 3.47 3.71

50:50 2.94 3.09 3.36 3.71 3.89 4.84

75:25 3.93 4.55 4.71 4.67 5.26 5.66

100:0 4.93 5.04 5.22 5.66 5.51 5.80

Tencel:

Cotton

0:100 2.29 2.34 2.55 2.69 2.96 2.29

25:75 2.89 2.94 3.60 3.88 3.99 2.89

50:50 3.72 4.22 4.42 4.57 4.83 3.72

75:25 4.83 4.73 5.21 5.44 5.74 4.83

100:0 5.04 5.22 5.66 5.51 5.80 5.04

a Tex twist factor

-90-

Fig. 4.11 − Variation in flexural rigidity with blend ratio of tencel blended ring yarns

spun at different twist factors [(a) Tencel-polyester, and (b) Tencel-cotton]

1

2

3

4

5

6

7

23.93 TF 28.71 TF 33.50 TF

38.28 TF 43.07 TF 47.85 TF

1

2

3

4

5

6

7

0 25 50 75 100

23.93 TF 28.71 TF 33.50 TF

38.28 TF 43.07 TF 47.85 TF

Tencel in blend, %

(a)

Fle

xura

l ri

gid

ity x

10

-3, g.c

m2

-91-

Fig. 4.12 − Variation in flexural rigidity with tex twist factor of tencel blended ring

spun yarns [(a) Tencel-polyester, and (b) Tencel-cotton]

0

2

4

6

8

0:100 TEN/PET 25:75 TEN/PET 50:50 TEN/PET

75:25 TEN/PET 100:0 TEN/PET

0

2

4

6

8

23.93 28.71 33.50 38.28 43.07 47.85

0:100 TEN/COT 25:75 TEN/COT 50:50 TEN/C0T

75:25 TEN/COT 100:0 TEN/COT

Tex twist factor

Fle

xura

l ri

gid

ity x

10

-3, g.c

m2

-92-

4.3.7 Hairiness

100% polyester yarn shows minimum hairiness followed by 100% cotton and

100% tencel yarns. The blended yarn shows intermediate value of hairiness (Table

4.8). The lowest value of hairiness for polyester yarn can be ascribed to long length,

low linear density and devoid of short fibres. The tencel yarn shows highest amount

of hairiness (Fig 4.13). Even though cotton is finest among the three, the presence of

short fibres in it leads to large number of hairs. With increase in twist factor, hairiness

decrease monotonically for all the yarns (Fig 4.14). This can be ascribed to the

reduction in length of spinning triangle.

-93-

Table 4.8 − Influence of blend ratio and twist factor on hairiness of tencel-polyester and tencel-cotton ring-spun yarns

Fibre

type

Blend

ratio

Hairs/10m

≥ 1mm ≥ 2mm ≥ S3

23.93a 28.71

a 33.50

a 38.28

a 43.07

a 47.85

a 23.93

a 28.71

a 33.50

a 38.28

a 43.07

a 47.85

a 23.93

a 28.71

a 33.50

a 38.28

a 43.07

a 47.85

a

Tencel:

Polyester

0:100 956 736 688 634 650 585 78 51 45 40 34 33 17 11 11 10 8 8

25:75 1075 800 787 780 702 675 91 56 55 52 47 37 20 12 12 12 11 11

50:50 1229 1008 974 914 887 864 135 91 80 75 70 69 31 20 17 15 15 8

75:25 1428 1152 1126 1101 1101 1079 179 129 125 120 111 107 43 31 28 27 26 25

100:0 1949 1670 1573 1463 1343 1341 338 278 249 230 220 212 109 96 85 53 81 77

Tencel:

Cotton

0:100 1923 1548 1208 1148 1076 1006 248 151 103 88 86 77 59 31 22 20 20 19

25:75 1734 1379 1240 1152 1001 973 188 140 112 99 83 80 39 33 26 23 23 20

50:50 1613 1330 1238 1059 1060 958 190 139 121 103 95 85 44 29 25 25 23 22

75:25 1694 1345 1281 1186 1133 1074 240 162 144 137 132 128 61 39 37 37 36 34

100:0 1949 1670 1573 1463 1343 1341 338 278 249 230 220 212 109 96 85 53 81 77

a Tex twist factor

- 94 -

Fig. 4.13 − Variation in hairiness with blend ratio of tencel blended ring yarns spun at

different twist factors [(a) Tencel-polyester, and (b) Tencel-cotton]

0

25

50

75

100

125

23.93 TF 28.71 TF

33.50 TF 38.28 TF

43.07 TF 47.85 TF

0

25

50

75

100

125

0 25 50 75 100

23.93 TF 28.71 TF

33.50 TF 38.28 TF

43.07 TF 47.85 TF

Tencel in blend, %

Hai

rs/1

0m

, S

3

- 95 -

Fig. 4.14 − Variation in hairiness with tex twist factor of tencel blended ring spun

yarns [(a) Tencel-polyester, and (b) Tencel-cotton]

0

30

60

90

120

150

0:100 TEN/PET 25:75 TEN/PET 50:50 TEN/PET

75:25 TEN/PET 100:0 TEN/PET

0

30

60

90

120

150

23.93 28.71 33.50 38.28 43.07 47.85

0:100 TEN/COT 25:75 TEN/COT 50:50 TEN/C0T

75:25 TEN/COT 100:0 TEN/COT

Tex twist factor

Hai

rs/1

0m

, S

3

- 96 -

4.4 Conclusions

4.4.1 Tensile behavior of tencel-polyester and tencel-cotton ring-spun yarns is

predominantly influenced by fibre composition and twist factor. Higher tencel content

results in less strength, reduced breaking extension and reduced work of rupture of

tencel-polyester yarns. However, for tencel-cotton yarns, there is an increase in

strength, breaking extension and work of rupture with the increase in proportion of

tencel fibre in the mix. Generally, the yarn strength and work of rupture increase

initially and then decrease with the increase in twist factor, and the optimum twist

factor shifts towards higher side as proportion of cotton in tencel-cotton mix

increases. Further, the breaking elongation of tencel blended yarns increases

consistently with the increasing twist factor.

4.4.2 The fibre composition as well as constituents of the mix markedly affects the

mass irregularity, which tends to improve with increase in polyester content in the

tencel-polyester mix. In the case of tencel-cotton yarns, mass irregularity increases

with the increase in proportion of cotton fibre. Generally, the tencel-polyester yarns

are more even and have fewer imperfections than the equivalent tencel-cotton yarns.

Twist factor has been found to change mass irregularity possibly due to change in

dynamic friction between fibres in the drafting field as speed of drafting alters with

twist.

4.4.3 Blending of tencel fibre either with polyester or cotton substantially increases

the yarn flexural rigidity. Higher twist factor has a deleterious effect on yarn rigidity.

4.4.4 Invariably, the yarns made with a tencel-polyester mix show less hairiness as

compared to tencel-cotton yarns, which further reduces with increase in polyester

content in the fibre-mix. Higher twist factor also results in considerable reduction in

hairs in all length groups.

4.4.5 In general, all tencel blended yarns produced with low level of twist are more

uniform, having less imperfection and flexible but less extensible and hairy. However,

tencel-polyester yarns are stronger at low twist level whereas tencel-cotton blended

yarns are stronger at high twist level.