AN INVESTIGATION ON THE MINIMUM TWIST OF COHESION
OF RING AND COMPACT SPUN YARNS
The major factors required for determining the optimum twist to be given to a yarn are the count of the yarn and the desired level of twist multiplier. These are the factors that are taken into account in the mill. But one of the other important parameters for determining the optimum twist to be inserted is the fibre cohesion, which is always neglected.
The minimum twist of cohesion, in twist per meter (tpm) is inversely proportional to the square root of the number of fibres in the cross section of the roving. The minimum twist of cohesion increases with micronaire index and decreases with fiber length at constant roving weight.
The compact spinning system[1], which was developed and is an improvement over ring spinning, has created much scientific and commercial interest over the last few years. The reason for better strength in this spinning system has been due to better fibre cohesion[2]. It was Barella( 1960 ) and his colleagues who did pioneering work on minimum twist of cohesion in rovings and yarns produced from wool and cotton[4]. Studies were also conducted for worsted yarns [3] For several years Barella’s concept was not utilized but now it plays a very important role in compact spinning, in view of its usefulness.
This work is concerned with the study of minimum twist of cohesion of various types of yarns differing in structure which differ in their structure and form.
2. Materials and methods
The yarn samples were subjected to various chemical treatments such as scouring , mercerizing, bleaching and dyeing, following usual methods. The yarn samples were conditioned at the standard atmosphere with relative humidity of 65+ 2% and at a temperature of 27+ 2 0C for 48 hours. Various chemical treatments such as scouring, mercerization, bleaching and dyeing, were given to the yarns. Both ring as well as compact spun yarn samples were used for the study.
2.2.1 Determination of minimum twist of cohesion of yarns
An instrument based on Barella’s technique was designed and fabricated. The instrument consisted of upper and lower jaws, and a specimen length of 25cm was fixed and the tension was kept at 0.1 gm/tex. Instead of following Barella’s method of determining minimum twist of cohesion, a departure was made. The minimum twist of cohesion (MTC) is given by the expression
MTC = Number of turns present in the yarn – Number of turns removed from the yarn x 100
Number of turns present in the yarn
The mean of 20 tests was considered.
2.3 Results and discussion
2.3.1 Effect of chemical treatments on MTC
From Figure 1 it can be seen that generally all the chemical treatments have led to a significant drop in the minimum twist of cohesion thus showing consolidation in yarns. From the graph it can be seen that the dyed fibers showed the best cohesion.
2.4.2 Effect of the type of fibre on MTC
The effect of different fibres on the minimum twist of cohesion is shown in Table 1. Among the yarns made of different fibres of the same count, viscose yarns show better cohesion, followed by polyester. The least cohesion is shown by cotton yarn.
2.4.3 Effect of blend composition on MTC
The effect of varying blend proportions on the MTC is shown is Table 2. The results show that in case of P/V blend, the blend proportion of 65:35 has better cohesion than the blend proportion of 75/25.This is due to the higher percentage of viscose content in the yarn. Viscose has higher fiber frictional value than polyester. In the case of P/C blend, the yarn having blend proportion of 75:25 has the greatest cohesion than the other proportions. This is because polyester content is maximum in this blend ratio and cotton content is minimum. Polyester has higher friction value than cotton fiber.
2.4.4 Variation of MTC in commercial samples
The comparison of MTC of yarns taken from various mills is shown in Table 3. Among the yarns of same count of 20s hosiery yarn, the yarn from mill G has the best cohesion. Among the yarns of 30s combed type, the yarn from mill A has the highest cohesion. This implies that in order to achieve the same cohesion in yarns, the same twist level and same fiber mixing should be used. Also it is possible to obtain high cohesion with lower twist per inch for a particular fiber type.
The comparison of MTC between carded, semi-combed and combed cottons is shown in Table 4. The results show that carded yarns have better cohesion than semi combed yarns. This is due to the draft given at carding (100 draft approximately) which reduces the trailing hook percentage. This in turn increases the compactness of the material by the increase of lateral pressure between the fibers.
2.4.6 Effect of different spinning methods on MTC
The comparison of MTC between ring and compact spun yarns is shown in Table 5. The results show that compact yarn showed better cohesion than ring yarn.
3. Conclusion
It is observed that scouring improves the cohesion of the yarn due to the removal of wax. The mercerization treatment further improves the cohesion over scoured materials. Bleaching exhibits further reduction in the minimum twist of cohesion. Reactive dyed yarns show better cohesion than those of previously treated yarns. Among yarns made of different fibers of the same count, viscose yarns show better cohesion. This is followed by polyester and the least cohesion is shown by cotton yarn. It is concluded that in a polyester/viscose blended yarn, the yarn having higher viscose content has the maximum cohesion. Similarly for polyester/cotton blended yarns, yarns having higher polyester content has better cohesion. It is also concluded that yarns of same cotton count from various mills have different cohesion values due to the variations in the fiber mixing. Also, the comparison between compact and ring spun yarns show that compact yarns have better cohesion. Finally, the comparison between carded, semi combed and combed yarns of the same count shows that there is a gradual decrease in cohesion from carded to combed yarns.
N.Gokarneshan1 , N.Anbumani2 , V.Subramaniam3
1 Department of Textile Technology, Kumaraguru College of Technology, Coimbatore – 641 006, Tamil Nadu, India.
2 Department of Textile Technology, PSG College of Technology, Coimbatore – 641 004, Tamil Nadu, India.
3 Formerly Department of Textile Technology, A.C.College of Technology, Anna University, Chennai – 600 025, Tamil Nadu, India.
