Characteristics of Imperfections in Cotton and Blend Yarns

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Indian Journal of Textile Research Vol. 13, December 1988, Pp. 192-197

Characteristics of Imperfections in Cotton and Blend Yarns

AAGUPTE

Textile Department, Victoria Jubilee Technical Institute, Matunga, Bombay 400 019, India and

N BALASUBRAMANlAN

The Bombay Textile Research Association, LB S Marg, Ghatkopar (West), Bombay 400 086, India Received 23 May 1988; revised and accepted 29 September 1988

Different yam properties like diameter, hairiness, weight per unit length, turns/em, fibre length, breaking strength and elongation have been studied at the thin and thick places and compared with that found in the normal portion of cotton and polyester/cotton yams to get a better understanding of the contribution of imperfections to yam quality. The actual diameter of thin place agrees with the calculated diameter but the actual diameter of thick place is much higher than the calculated diameter. The tenacity of thin places is lower compared to that of normal portion. the effect being more prominent in polyester/cotton blend yam. Thick place, however, has nearly the same tenacity as the normal portion.

Keywords :Breaking strength, Cotton yam, Elongation, Imperfections, Polyester/cotton yam, Yam hairiness

1 Introduction

Imperfections in yarn not only influence the ap- pearance of yarn and fabric but also the perform- ance of yarn in weaving. The causes of higher levels of thin and thick places in yarn may be found either in the raw material or in imperfect prepara- tion processes'. Although a number of studies"?

have helped in understanding the process parame- ters affecting the level of thin and thick places in the yarn, the general level of imperfections in In- dian yarns is many times higher than international norms and is one of the reasons for our relatively poor share in the export market. Gupta and Vi- jayshanker'' have shown that small fragments of seed-coats present in the sliver, as a result of un- satisfactory ginning, result in blemishes like neps, thick places and classimat A and B faults in the yarn. In medium count yarns, there is a well-de- fined quantitative relationship between the fre- quency of blemishes in yarn and the percentage seed-coat content in the sliver used to spin the yarn. Further, Gupta et al.⁹ have shown that most of the blemishes in fine count yarns originate from the short and immature fibre bunches that are generated during ginning from the immature seeds and ovules present in the seed cotton itself and concerted efforts would have to be made to overcome the problem of occurrence of excessive immature seeds and ovules in our cottons. While analyzing yarn imperfections, Balasubramanian et

al." found lack of agreement between mass and

diameter of imperfections, suggesting that the structure and composition of the imperfections could also vary. The thin places were totally free from foreign matter and immature ovules, while fibre cluster and foreign matter contributed 60- 90% of thick places. Immature ovules and foreign matter contributed to about 75% of the total number of neps.

A critical study of the physical properties of yarn at thin and thick places will provide a clue to their formation. The way in which the yarn properties are modified at these places compared to that found in normal portion will facilitate a better understanding of the contribution of imperfections towards yarn quality. Therefore, in the present study, different yarn properties like diameter, hairiness, weight per unit length, turns/em, breaking strength and elongation have been studied at the thin and thick places and compared with that found in the normal portion of yarn.

2 Materials and Methods

Different combed cotton yarn samples and polyester/cotton blended yarn samples collected from the mills were used (Table 1).

Samples were run through Uster evenness tester and with the help of yarn imperfection selec- tor 50 thin places (at - 50% sensitivity) and 50

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Table 1- Mixing and Blend Percentage of Yam Samples

Yarn Count Mix Cotton Percentage Composition of blend

Tex (Ne)

15 Combed (40) A DCH32 83

MCU5 17

10 Combed 1(0) A DCH32 83

MCU5 17

6 Combed (1001 B Suvin 83

DCH32 17

15P/C (40) Blend C Polyester 45 Terene 1.5 d, 45 mm

Cotton 55 Cotton Mix.A

12 PIC (50) BlendD Polyester 67 Terene l.2 d, 38 mm

Cotton 33 Cotton Mix. A

10PIC HT (60) Blend D Polyester 67 Terene l.2 d, 38 mm

Cotton 33 Cotton Mix. A

PiC - Polyester/Cotton; and HT - High twisted.

thick places (at 3 sensitivity, i.e.

+

50%) were collected. Without allowing the twist to be lost each sample was fixed with cellotape on a paper frame having window size of 1 cm x 7.5 cm. While fixing the sample on paper frame, thin place/thick place in the yam was kept in the central position of 7.5 ern yam length mounted on the paper frame.

Then 50 samples were prepared by taking normal yam portions which is a randomly selected portion from the bobbins (5 specimens were taken from each of ten bobbins every time).

The samples were tested on Projectina for yam diameter, hairiness and then on Instron for single thread strength and elongation percentage of thin places, thick places and normal portions of yam.

Yam hairiness was measured by the method of Subramanian et al," which is a modification of Je- dryka's method'<. For single thread strength, yam samples from paper frame were mounted between two jaws of Instron at a gauge length of 7.5 em and the paper frame was cut before testing. After the test, the broken specimen was cut close to the jaw and weighed for yam count and tenacity de- termination. The count was based on 7.5 em length of yarn in these tests.

For determining the weight per unit length of normal, thin and thick places, the yarn was put under a tension of tex/2 and a length of 1 em was cut and weighed. For thin and thick places the respective fault length of 1 cm was cut and weighed.

Table 3 shows the actual weight per unit length of thin and thick places. It is pertinent to mention here that the values of yarn count given in Table 7 are based on the weight of 7.5 em length, which includes a thin or thick place. Therefore, there is some difference between the two weights, the weight of thin places in Table 3 being lower

than that in Table 7 and the weight of thick places in Table 3 being higher than that in Table 7.

Further, 20 samples each of normal, thin and thick places were tested for twist per unit length on twist tester with a gauge length of half an inch.

Fibre length was also measured at these places.

For this purpose, thin and thick places were collected, untwisted and fibres from the respective portions were tested for fibre length. Each fibre was straightened on a glass plate with the help of a few drops of paraffin oil smeared on the plate.

The length of each individual fibre was measured with a scale in mm. Five hundred fibres were measured for each sample.

3 Results and Discussion

3.1 Yam Diameter

Table 2 shows average yarn diameter at normal, thin and thick places of yarn. It is seen that the diameter of thin places is around 70% of the normal yarn diameter and there is not much variation between the samples. The diameter of thick places is more than 150% of the normal yam diameter and there is variation between the samples.

A thin place recorded with sensitivity - 50%

on Uster indicates the presence of yam mass less than 50% of the average value which is proportional to (tex/Z). Since the yarn diameter is proportional to ~ the thin place will have a diameter proportional to ]tex/2 or (0.707) ^(v~). The diameter of thin place will be therefore (0.707) times normal yarn diameter.

On the same basis, sensitivity position 3 (i.e.

+

50%) for thick places will indicate presence of yam mass 1.5 times its average value which is

193

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INDIAN J. TEXT. RES., VOL. 13, DECEMBER 1988

Table 2- Yam Diameter (Actual and Calculated) at Normal, Thin and Thick Places

Actual yam diam (rom) Calculated yam diam (rom) Actualdiam

x100

Normal Thin Thick Thin Thick Calculated diam

portion place place place place

Thin Thick

place place

0.1499 0.1040 0.2360 0.106 0.184 98.11 128.54

(69.38) (157.44)

0.1289 0.0910 0.2760 0.092 0.159 98.91 173.58

(70.67) (214.12)

0.0942 0.0627 0.\732 0.067 0.115 94.14 150.61

(66.56) (183.86)

0.1491 0.1006 0.2293 0.106 0.184 94.91 124.62

(67.47) (153.79)

0.1235 0.0891 0.2186 0.087 0.151 102.41 144.77

(72.15) (177.00)

0.1062 0.0757 0.2229 0.075 0.131 100.93 171.46

(71.28) (209.89) Sample

15 Combed 10 Combed 6 Combed

15 PIC 12P/C lOP/CHT

P/C- Polyester/cotton; and HT - High twisted.

Values in parentheses indicate percentage with respect to normal.

equivalent to a yam diameter (1.225) times normal yam diameter.

The yam diameter values for thin and thick places were calculated from the actual diameter of normal portion using the above relationships and the results are given in Table 2. It is seen that the actual diameter values of thin places agree very well with the calculated values. But the actual diameter values of thick places are much higher than the calculated values. This may be partly because thick portions are undertwisted and are, therefore, more bulky in relation to normal portions and the influence of twist on diameter is more at lower levels of twist than at higher levels.

The reduction in diameter with increase in twist is more prominent at low twists and it decreases progressively with increase in twist.

3.2 Weight per Unit Length

The actual weight per unit length of the yam at thin and thick places was compared with that of the normal portion of yam. Table 3 shows that the weight per centimeter of thin places is 60%

and that of thick places is around 150% of the normal portion. Since thin places should include only those portions whose weight is less than 50%

of the average, the sensitivity level in actual prac- tice is different from that indicated in the instru- ment. Portions up to or even above 60% of the normal seem to get counted as thin place.

3.3 Turns/em

Turns/ cm in normal, thin and thick places are given in Table 4. It is seen that turnslcm at thin

Table 3-Weight per Unit Length of Yam at Normal, Thin and Thick Places

Sample Actual wt/cm (l1g)

Normal portion Thin place Thick place

15 Combed 164.78 101.90 249.04

(61.84) (151.13)

10 Combed 99.04 63.36 155.80

(63.97) (157.31 )

6 Combed 59.26 35.00 87.00

(59.02) (146.71)

15 PIC 149.84 93.34 216.70

(62.28) (144.66)

12 PIC 112.90 69.30 174.20

(61.38) (154.33)

lOP/CHT 99.24 60.03 141.50

(60.76) (142.58) Values in parentheses indicate percentage with respect to normal.

places are 150% and at thick places 70% of those at normal portions of yam. It is, therefore, ob- served that thin places, which have generally 60%

of the normal yam weight, are overtwisted to the extent of 150% of the normal yam twist. Similar- ly, thick places, which have 150% of the normal yam weight, get lower twist to the extent of 70%

of the normal yam twist.

3.4 Yarn Hairiness

Table 5 shows that the yam hairiness at thin places is about 35% and at thick places above 150% of the normal yam hairiness. For 10 PIC yam, which is high-twisted, the hairiness is com- paratively lower. The thick places which have

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more than 150% normal yam diameter and weight per unit length are expected to have more hairiness in yam as the number of fibres in a cross-section is likely to be more. Moreover, these places are soft twisted which would also result in more hairiness. Thus, the increase in incidence of thick and thin places will lead to more variability in hairiness.

3.5 Fibre Length

Table 6 shows that mean length and length CV/o for different samples do not differ much for thin and thick places of yam. For 15 and 10 combed samples, the fibres shorter than 16 mm are more at thick places than at thin places of yarn. For 6 combed sample, there is no difference in the percentage number of fibres shorter than

16 mm at thin and thick places.

The other workers have found more short fibres at thick places than at thin places of yarn".

All the samples used in this study were combed and, therefore, the percentage short fibres is lower compared to that for carded samples and this may be one of the reasons why not much difference in short fibre content is seen between thick and thin places in the present study.

3.6 Yarn Strength

Single thread strength and elongation-at-break for normal, thin and thick places are given in Table 7. The table also gives the tenacity (g/tex]

values calculated from the tex values of the tested samples. As expected, the breaking strengths of thin places are lower and those of thick places higher than the breaking strengths of normal portions. When the strength is corrected for weight per unit length, the thin places are found to be weaker compared to the normal portions in 5 out of 6 cases. The thin places in polyester/cotton blend counts 12 and 10 in particular have a much lower tenacity than that of the normal portion.

This means that some disturbance in the spinning process has resulted in the formation of a thin place and hence the intrinsic strength or tenacity is reduced. The thick places, however, have nearly the same tenacity as of the normal portion except in 6 combed and 12 PIC where the tenacity of thick place is lower.

Elongation % of thick places is higher than that of normal portion in cotton yam. This is, however, not true for polyester/cotton blended yarn.

Elongation % for thin places is lower than that of normal portion, the difference being very

Table 4- Twist Level in Normal, Thin and Thick Places Table 5- Yam Hairiness in Normal, Thin and Thick

Sample Turnslem Places

Sample Hairiness (mm)/10 em

Normal portion Thin place Thick place

15 Combed 9.80 14.45 6.77 Normal portion Thin place Thick place

(147.4) (69.1) 15 Combed 45.86 19.11 61.37

10 Combed 14.70 22.44 10.00 (41.67) (133.80)

(158.4) (70.6) 10 Combed 39.25 14.11 83.35

6 Combed 18.66 29.53 12.01 (35.95) (212.36)

(158.3) (64.4) 6 Combed 32.34 13.89 52.26

15 PIC 11.34 16.26 9.06 (42.95) (161.60)

(143.4) (79.9) 15 PIC 35.80 11.03 61.45

12PIC 12.87 18.50 8.86 (30.81) (171.65)

(143.7) (68.8) 12PIC 27.34 9.26 60.19

10PICHT 17.60 28.39 15.67 (33.69) (220.15)

(161.3) (69.0) 10PICHT 27.93 8.53 41.31

(30.54) (147.91) Values in parentheses indicate percentage with respect to

normal. Values in parentheses indicate percentage with respect to

normal.

Table 6-Fibre Length at Thin and Thick Places

Sample Thin places

Mean Length Fibres Mean

length CV% <16mm length

0/0

15 Combed 30.28 24.26 5.2 31.42

10 Combed 28.95 24.79 3.8 27.46

6 Combed 30.66 24.40 3.6 31.40

Thick places Length

CV/o

Fibres

<16mm 0/0 25.37

26.98 22.29

7.6 10.2 3.4

195

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INDIAN 1. TEXT. RES., VOL. 13, DECEMBER 1988

Table 7 -Single Thread Strength and Elongation % in Normal, Thin and Thick Places

Yarn count Breaking load Tenacity Elongation

tex CV'/o

15 Combed

Normal portion 15.90 12.18

Thin place 12.03 8.54

Thick place 18.61 11.51

10 Combed

6 Combed

15 PIC

12 PIC

10PICHT

g CV'/o g!tex CV'/o E% CV'/o

288.24 16.66 18.07 8.49 7.53 11.04

233.12 10.17 19.42 9.05 7.19 12.09

332.40 14.76 17.85 8.49 8.30 9.65

185.06 14.80 18.48 7.69 8.08 to.78

145.00 14.03 16.96 9.63 7.82 11.15

228.04 16.01 17.96 9.48 8.99 to.33

114.60 19.19 20.11 13.56 6.21 14.62

81.64 12.44 17.90 13.09 6.15 12.78

124.22 17.12 17.62 12.25 6.89 10.67

236.06 13.01 16.09 6.52 12.32 20.05

169.14 10.14 15.67 11.53 8.52- 15.78

259.00 11.51 15.85 8.93 11.38 15.91

282.70 17.16 26.17 9.95 12.60 14.70

182.52 12.79 20.79 13.11 9.60 14.53

310.32 15.11 22.42 13.05 12.35 11.98

206.42 20.23 20.54 13.09 14.48 15.25

136.06 16.79 17.74 16.08 10.58 19.08

233.44 17.00 20.60 11.03 13.89 12.82

350

POLYESTER ItOTTON YARN TEX - 12

1.00 No - 50

320

200

160

..

o---THICK PLACES .-NOR"Al PORTIONS .-THIN PlACES

10 12 U.

ElONGATION, v,

120LL- _

5 6 16

Fig. l=-Breaking strength and elongation at normal, thin and thick places of yarn

prominent in polyester blend. The lower elongation arises because the break is completed earlier because of the lower strength of the thin portion.

The drop in elongation from normal to thin por-

tion is most marked in polyester/cotton blended yam. A flatter slope for strength-elongation relationship is also seen in thin places for such yarns (Fig. 1). The same trend is found in 10 PIC and 15 PIC yarns. Fig. 1 also shows a good correlation between strength and elongation for the three types of yarn samples. The correlation coefficients for normal, thin and thick places are 0.8443, 0.7274 and 0.7925 respectively.

4 Conclusions

4,1 The diameter of thin places is around 70%

and that of thick places more than 150% of the normal yarn diameter. The actual diameter of thin places agrees very well with the calculated diameter but the actual diameter of thick places is much higher than the calculated diameter.

4.2 The weight per unit length of thin place (at - 50% sensitivity level) is 60% while that of thick place (at

+

50% level) is around 150% of the normal yarn weight, indicating that the Uster counts as thin places the portions thicker than the designated sensitivity level.

4.3 Turns/em at thin place are 150'% and that at thick place 70% of the normal value.

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4.4 Hairiness at thin place is 35% and that at thick place 150% of the normal yam hairiness. In- crease in incidence of thick and thin places will, therefore, lead to higher variability in hairiness.

4.5 The mean length of the fibres or CV/o of fibre length does not show any significant difference at thin and thick places.

4.6 Breaking strength of thin places is lower and that of thick places higher than the normal yam strength. The tenacity of thin places is also lower than that of normal yam, the effect being more prominent in polyester/cotton blended yam.

Thick place, however, has nearly the same tenacity as the normal yam.

4.7 Elongation % of thick places is higher than that of the normal yam in cotton yam. Elongation

%of thin place is lower than that of normal yam, the difference being more prominent in polyester/

cotton blend.

References

1 Furter R, Evenness testing in yam production, Pari I(The Textile Institute, Manchester) 1982, 33.

2 Garde A R and Sethi J,Proceedings,11th joint technolog- ical conference of Al1RA, BTRA and SITRA (South India Textile Research Association, Coimbatore) 1969,1.

3 PomfretWR, Text Month,10(1971)67.

4 Subramanian T A, Bandyopadhyay S and Garde A R, Proceedings, 13th joint technological conference of Al1RA, BTRA and SITRA (Ahmedabad Textile in- dustry's Research Association, Ahmedabad) 1972, 63.

5 Bandyopadhyay S, Garde A R, Subramanian T A and Raj B S,JText Assoc,33(1972) 65.

6 Shankaranarayana K S, Govindarajulu K and Krishnaswa- my N, Proceedings, 14th joint technological conference of A l1RA , BTRA and SIrnA (South India Textile Re- search Association, Coimbatore) 1973,55.

7 BaIasubramanian N, Viswanathan K and Gupta K R, Prlr ceedings, 17th joint technological conference of Al1RA BTRA and SITRA (South India Textile Research As- sociation, Coimbatore) 1976,41.

8 Gupta A K and Vijayshankar M N, J Text Inst, 76 (1985) 393.

9 Gupta A K, Shah P H and Subramanian T A, Proceed- ings, 27th joint technological conference of ATIRA BTRA, SITRA and NITRA (Northern India Textile Re- search Association, Ghaziabad) 1986,21.

10 BaIasubramanian A, Padmanabhan A Rand Seshen K N, Proceedings, 27th joint technological conference of ATlRA, BTRA, SITRA and NITRA (Northern India Textile Research Association, Ghaziabad) 1986,21.

11 Subramanian T A, Grover J M and Salhotra K R,JText Inst,62 (1971) 424.

12 JedrykaT, Text ResJ, 33(1963)663.