163 CHAPTER 8 DEVELOPMENT AND PROPERTIES OF AIR JET-ROTOR SPUN YARNS 8.1 INTRODUCTION Innovations are required in rotor spinning for improving the quality of yarn so that its application becomes quite widespread in all spheres of textiles. A considerable amount of work has been carried out on the characteristics of yarns produced with air-jets in conjunction with ring spinning. Ramachandralu (2002), Basu (2001) and Subramanian et al (2007), have shown the improvements in hairiness of yarns produced with air-jet nozzles. However these yarns were ring spun based structures which inherently are less uniform than rotor yarns. So any modification in the ring structures such as the addition of jet-spinning may not tremendously enhance some properties such as uniformity. Therefore, efforts were undertaken in this study to introduce jet-spinning to rotor technology with the aim of enhancing the properties of rotor yarn. It was Kalyanaraman (1992) who showed that by introducing a tube after the yarn formation and by passing compressed air through it, the hairiness could be suppressed. Wang et al (1997), used a single air-jet below the yarn forming zone of a conventional ring spinning system and found that there was considerable improvement in hairiness. The effects of air-jet design on the properties of air-jet ring spun yarns have been examined by Subramanian et al (2007).
164 Chongwen Yu (1999) has studied the characteristics of open-end jet yarn by fabricating a device which combines the advantages of both air-jet twisting and open-end spinning. Attempts were made in the past for improving the performance of rotor spun yarns by introducing long staple viscose fibers which led to the formation of wrapper fibers (Sengupta et al 1980). As is evident from the foregoing brief introduction, there is a dearth of knowledge and data on the development and characteristics of jet-rotor spun yarns. More importantly, to the authors best knowledge, there is hardly any data on the characteristics of cotton yarns spun using the combinatorial approach. The present work reports a novel approach to improve the properties of rotor spun yarns which are known for their weak strength compared to ring spun yarns. This chapter presents the study of the development of cotton yarns spun on the combinatorial system involving rotor spinning followed by air-jet spinning. An air-jet was introduced between the yarn discharge tube in rotor spinning and the take-up device. The procedures followed and the characteristics of the jet-rotor yarns and conventional rotor yarns are discussed in the subsequent sections of the chapter. The information provided by Wang (1977) who has carried out studies on the effect of speed on the hairiness of yarns was very helpful. They demonstrated that a higher speed of yarn had led to an increase in hairiness but it reduced the standard deviation. Test speed was found to have little effect on the yarn evenness. These findings are very relevant and provide essential guidelines for interpreting the results of the study. 8.2 MATERIALS AND METHODS These are given in chapter 3.
165 8.3 RESULTS AND DISCUSSION 8.3.1 Yarn Hairiness Since the main focus of the study was on yarn hairiness, it was examined by two methods, namely, by using Uster Evenness and Premier iq Quality Center. The results obtained are presented in Table 8.1. Table 8.1 Hairiness of yarns S. No. Particulars Uster Hairiness Index S3 (No. of hairs equal to or longer than 3 mm) 1 Rotor yarn 5.81 143 2 Jet rotor yarn 4.53 72 For the purpose of hairiness comparison, S3 (Hair/cm) values obtained from the Premier iq Quali Center tester was used. It was evident that the hairiness of air-jet rotor spun yarns was lower than that of the conventional rotor yarn. There is almost a 50% reduction in yarn hairiness in air-jet rotor yarns as compared with conventional rotor yarns. To support the above results, optical microscope imaging was done on the jet-rotor and conventional rotor yarns. Figures 8.1 and 8.2 show the surface appearance of two yarns. As it is evident from the figures, it is clear that the air-jet rotor yarns have less number of hairs on their surfaces compared to conventional rotor yarns.
166 Figure 8.1 Optical image of rotor spun cotton yarn Figure 8.2 Optical image of air-jet rotor spun cotton yarn 8.3.2 Yarn Tensile Properties Table 8.2 gives the tenacity results of rotor and jet-rotor yarns evaluated using Uster Tenso Jet tester. It is clear from the results that the airjet rotor cotton yarn is characterized by slightly higher strength than the conventional rotor spun yarn. As far as the elongation is considered, it was noticed that the conventional and air-jet rotor spun yarns exhibit more or less similar values. The air jet rotor spun yarn shows an increase of 4% in tenacity. All other yarns such as air-jet, friction and self-twist yarns may have lower tenacities than ring spun yarns owing to their different yarn structural differences. The increase in strength of air-jet rotor spun yarns compared to the conventional rotor yarns may enable its application in apparel sectors.
167 Table 8.2 Tensile properties S. No Particulars Tenacity (gf/tex) Elongation (%) 1 Rotor yarn 12.38(14.2) 4.8(25.5) 2 Airjet rotor yarn 13.23(7.2) 4.06(19.2) 8.3.3 Yarn Evenness Yarn evenness results are given in Table 8.3. As is evident from results, a slight deterioration in the air-jet rotor spun yarn quality has been observed. However, there is a noticeable reduction in thin places for air-jet rotor spun yarns compared to the conventional rotor spun yarns. The introduction of air-jet after the yarn formation in rotor spinning may have altered the coherent structure of the rotor yarn resulting in increase in thick places and neps. However, the air-jet rotor yarns would be bulky giving cushion effect. Such bulky loose structures may result in soft but strong yarns which can be used for developing high quality fabrics. Table 8.3 Yarn evenness results S.No. Particulars U% Thin (-50%) Thick (+50%) Neps (+200%) 1 Rotor yarn 11.54 12 24 17 2 Airjet rotor yarn 11.88 8 49 46 8.3.4 Yarn Abrasion Resistance Table 8.4 gives the yarn abrasion resistance and the relative resistance index values for the yarns studied. It is evident from the results that
168 air-jet rotor spun yarns have more abrasion resistance than conventional rotor spun yarns which is reflected in higher resistance cycle values. RRI = Mean Resistance (cycles) Pretension (cn/tex)/ Tex (8.4) Relative resistance index values also follow a similar trend. Abrasion study shows that the air-jet rotor yarns will have enhanced abrasion resistance than conventional rotor yarns. This result will lead to superior weaving performance of jet-rotor spun yarns. Table 8.4 Yarn abrasion parameters S. No Particulars Abrasion resistance (cycles) Relative Resistance Index 1 Rotor yarn 29 106 2 Airjet rotor yarn 44 162 8.3.5 Packing Factor Table 8.5 gives the packing factor values for conventional and airjet rotor yarns. It is clear that the air-jet rotor spun yarns are characterized by higher packing factor when compared with conventional rotor spun yarns. This implies that the air jet rotor spun yarns are more compact and may be the reason for higher strength of jet-rotor spun yarns. Table 8.5 Yarn packing factor values S. No Particulars Yarn Dia (cm) Specific Volume (cc/g) Packing Factor 1 Rotor yarn 0.0273 1.987 0.33 2 Airjet rotor yarn 0.0208 1.154 0.58
169 8.3.6 Swelling Index The parameter swelling index is very sensitive to yarn structure and any treatment such as resin finish which is applied to the textile yarns. Table 8.6 gives the swelling index of the air jet rotor spun and the conventional rotor spun yarns. That the swelling index of air jet rotor spun yarns is significantly lower than that of the conventional rotor spun yarn can be noticed. This provides further evidence that the air jet rotor spun yarns exhibit more compactness vis-à-vis conventional rotor spun yarns. Table 8.6 Swelling index of yarn S.No. Particulars Swelling index 1 Rotor yarn 1.67 2 Airjet rotor yarn 1.14 8.4 CONCLUSION A novel methodology has been adopted in this work to develop superior quality yarns for apparel use. Rotor spun yarns have been subjected to swirling air-jets to compact and enhance their strength. The process of developing and the characteristics of jet-rotor cotton yarns have not been hitherto reported in any scientific literature. Jet-rotor cotton yarns have been found to have higher strength and compactness compared to their conventional rotor counterparts. Irregularity of jet-rotor yarns increases slightly than the regular rotor yarns. However, for some applications such as fancy yarns with bulkiness, this issue may not be a deterrent factor. Overall, the combinatorial process involving rotor spinning followed by air-jet injection leads to superior quality yarns that can find good use in developing next generation apparel fabrics.