Improvement in spinning of yarn from dyed fibre

Spinning of yarn from dyed fibre could be improved by compacting technology significantly, writes A Kanthimathinathan.

In India, the textile industry is the second largest sector, next only to agriculture in terms of its contribution to income (GDP) and employment of the nation. For centuries, it is evolving in process of production, varieties and quality of products and technological progress and cost effectiveness. From the stage of raw cotton to final products, the industry have processes like ginning, spinning, weaving, dyeing and processing and garmenting. Efforts to improve efficiency in yarn manufacturing and increasing the returns in textiles involve any activity that improves productivity and reduces cost. With free trade economy and abolition of all trade barriers, international trade became intensively competitive and the stakeholders have become aware of the need to remain competitively efficient.

Technological and entrepreneurial innovations have sustained the growth of the industry, with support in policies and finance for value additions and export. In this context, attention is drawn to the impact of dyeing on strength of the fibres that goes to manufacturing of yarns also dark shades in yarn, lower productivity in spinning, higher incidence of fluff on yarn. These reduce quality of yarn and its CSP.

Preliminary investigations in spinning process of yarn from dyed fibres is summarised as below:

During preliminary investigations, (i) the characteristics of dyed fibres, (ii) in-process materials such as card sliver, comber sliver, draw frame sliver, roving and yarn such as evenness (U%) & yarn imperfections, CSP, hairiness and performance such as end breakage in spinning & rewinding breaks in winding and classimat fault level in final yarn are analysed. Additionally, the reduction in production rates of machinery also is studied.

Dyed fibre characteristics

The mean length and fibre bundle strength are are presented in Table 1. In the case of mean length, measured in HVI, there is a length loss of 12 to 21 per cent. The loss is small in light shade (12 per cent) and the largest in dark shade (21 per cent). Bundle strength loss is maximum in dark shade (12 per cent).

Carding

In carding process, the unevenness of sliver (U %) is tested. The production rates maintained in carding of light, medium and dark shades are also compared.

Sliver evenness (U%) is also reduced in light shades by 6 per cent to 10 per cent, in medium shades by 15 per cent to 25 per cent and 27 per cent to 50 per cent in dark shades. This deterioration can be easily understood as reduction in mean length of the dyed fibre vis-à-vis grey fibre. The reduction in sliver evenness could be due to fibre rupture in carding process. It is due to lower fibre strength and higher inter fibre friction in the case of dyed fibres. It results in the reduction of carding production to the extent of 3 per cent to 34 per cent than grey fibre. It is also noticed that minimum production loss varies from 3 per cent to 34 per cent dyed fibres of these shades.

Combing

In combing process, the noil extraction, the sliver unevenness and production rate are also studied and reported. Due to fibre rupture that occurs in blowroom and carding process, the combing process warrants high noil extraction and it is observed that it increased from six to 11 per cent in light shades, 8 per cent to 30 per cent in medium shades and 25 per cent to 50 per cent in dark shades.

Roving

Roving evenness and production rate are measured for dyed cotton fibres in Roving process. The roving unevenness increases from 4 per cent to 11 per cent in light shades, 9 per cent to 19 per cent in medium shades and 21 per cent to 34 per cent in dark shades.

Ring Spinning

In ring spinning, the production rate (grams per spindle per 8 hours), end breaks, yarn hairiness, total imperfections and yarn strength (CSP) have been studied and reported in Tables 3(a) and 3(b). The end breaks are in ascending order as dyed fibre content is increased.

The increase in end breaks per 100 spindle hours ranges from 33 per cent to 70 per cent in light shades, 130 per cent to 200 per cent in medium shades and 220 per cent to 280 per cent in dark shades.

The yarn imperfections and yarn strength are the primary characteristics of yarn which have commercial impact . Both show decline in dyed fibre. It is on the higher order from dark to light shades. Yarn imperfections in light shades are 9 per cent to12 per cent, in medium shades it is 38 per cent to 90 per cent and in dark shades it is drastically deteriorated to 74 per cent to 219 per cent. Deterioration in yarn imperfections could be due to the uncontrolled movement of dyed fibres in the drafting zone attributable to friction loss and migrating tendency. As the imperfections in yarn increase, the strength drop is inevitable. The yarn strength in terms of CSP deteriorates 2 per cent to 20 per cent in light shades, 7 per cent to 24 per cent in medium shades and in dark shades it is 16 per cent to 29 per cent.

Three levels of combination of dyed cotton fibres (X,Y,Z) were studied for important quality differences from pure grey fibre (G).The attention was on fibre characteristics and changes in important properties in each of the processes viz., carding, combing, drawing, roving and ring spinning. In each of the characteristics there were adverse changes –that reduce the quality and value of the end product of the spinning mills-yarn. This decline in yarn quality as compared to grey fibre (G), increased as the dyed fibre content has increased in fibre combinations (i.e., the percentage of the dyed fibre increased in fibre inputs) X,Y and Z. Thus the inference is: in the process of spinning, the quality of yarn, larger the content of (% share) dyed fibre in cotton fibre inputs and the effect is statistically significant at five percent level(chi square tests).

Alongwith the loss of quality of fibre due to its dyeing and also as a consequence of it, there is a significant deterioration in production rate (or productivity) of the spindle .The deterioration is also increasing as the dyed fibre content increases .The implication of these influences is that, while dyeing is inevitable for cotton fibres, to protect the quality of yarn and return to it, the blend proportion of the dyed fibre in input of the spinning mills need to be optimised.

Objectives of the present study include: To study the effect of mechanical compacting systems and suction compacting systems to improve dyed fibre spinning; to assess the improvement in aesthetic and tensile properties of yarn; and to improve the spinning performance of yarns made with dyed cotton fibres.

Materials and Methods

The cotton variety used in this process is S6 Cotton fibre. S6 Cotton variety has been used as raw material for this study with 29.2mm length/Mic of 3.8/22.2 gm per tex/with SFC(n) of 23.5. With this cotton fibre, we have prepared three different mixings as below:

• 100 per cent undyed fibre (to produce grey yarn)
• 20 per cent dyed and 80 per cent undyed fibre (to produce medium dyed yarn)
• 45 per cent dyed fibre and 55 per cent undyed fibre (to produce dark shade yarn)

From this mixing we produced yarn in controlled conditions with this following process flow. Process flow chart upto Roving bobbins is given in the Table 4 below:

Tests carried out on these nine different types of samples. All these yarns are tested for the following characteristics: Zweigle yarn Hairiness, Uster evenness and imperfections, and tensile behaviour.

Results and discussion

Yarn Hairiness: Yarn hairiness of nine different yarn samples are as given below in Table 6.

In grey yarn, the percentage of reduction in yarn hairiness is 91 and 93 per cent in mechanical and pneumatic compacting respectively. In medium shade yarn, the percentage of reduction in yarn hairiness is 46.9 per cent and 61.4 per cent and the reduction in pneumatic compacting is more than mechanical compacting. In dark shade yarn, the reduction in yarn hairiness is 49.7 per cent and 51.3 per cent and the trend of reduction is equal in both the types of compacting system. Thus, both compacting systems are able to control the migrating tendency of dyed fibres to a significant extent and the improvement is consistent in the case of mechanical compacting. In pneumatic compacting system, the reduction in yarn hairiness is reduced as the level of dyeing is increased.

Yarn unevenness and imperfections

Yarn Unevenness and imperfections as measured in Uster yarn evenness tester is given in Table 7.

Reduction in uneveness in mechanical compacting yarn and suction compacting yarn in grey yarn is 15 and 17 per cent respectively, which is statistically significant. The trend of reduction is continued in medium and dark dyed yarn. In the case of yarn imperfections, the reduction level in grey yarn is 44 per cent and 42 per cent in mechanical compacting and suction compacting systems. However in the case of dark dyed yarn, the reduction trend is diminished to the level of 36 per cent in mechanical compacting and 22 per cent in the case of suction compacting.

Tensile properties

Tenacity and elongation as measured in Tenso rapid is given in Table 8. In medium and dark shade yarn, the tensile strength of yarn is improved significantly compared to grey yarn. If we compare the normal grey yarn strength against medium dyed compact yarn (both MC and SC) we find it is better. However in the case of dark shade yarn, there is a drop of 1.1 and 2.3 per cent strength drop in mechanical compacting and suction compacting in comparison to normal grey yarn, which is not significant.

Yarn quality index

Yarn quality index is estimated for all the types of yarn and impact on dark shade alone is reported in Table 9. Yarn quality index significantly is improved in mechanical and pneumatic compact yarn in both medium shade and dark shade. ANOVA is applied and we find the improvement is statistically significant.

Conclusion

Spinning of yarn from dyed fibre could be improved by compacting technology significantly. As the compact medium shade and dark shade yarn exhibit higher yarn strength, it will help in improving the productivity in spinning also.

References

1) M. Nicoloai, A.Nechwatal and K.P.Miek , “ Textile Crosslinking of Reactions to Reduce Fibrillating Tendency of Lyocel fibres”, Textile Research Journal.
2) O.L. Shanmuga Sundaram.and S.Kumaravel, “Role of Enzymes in Textile Processing Industry”, Asian Dyer, 3(.): 44, 2005.

A Kanthimathinathan is CEO, WINSYS SMC, 18, North Avenue, Texpark, Civil Aero Post, Coimbatore – 641014. Can be contacted on: Email: kanthi.q@gmail.com.