Indian Journal of Fibre & Textile Research Vol. 38, September 2013, pp. 237-243 Studies on elastane-cotton core-spun stretch yarns and fabrics: Part I─Yarn characteristics A Das a & R Chakraborty Department of Textile Technology, Indian Institute of Technology, New Delhi 110 016, India Received 24 July 2012; revised received and accepted 22 September 2012 The present paper reports the interaction effect of elastane stretch, proportion of elastane core and twist multiplier on physical and mechanical properties of stretchable elastane-cotton core-spun yarns. The core component is 78 dtex elastane filament and the sheath consists of cotton. The core-spun yarns are produced in a modified ring frame. A three-variable factorial design technique, proposed by Box & Behnken has been used to study the combined interaction effect of the above variables on various yarn characteristics, like tenacity, breaking elongation, yarn-to-metal friction, elastic recovery and hairiness. It is observed that the above parameters have significant impact on all the yarn characteristics except breaking elongation. Keywords: Core-spun yarn, Elastane filament, Elastic recovery, Hairiness, Yarn-to-metal coefficient of friction 1 Introduction Stretchable fabrics are now-a-days used widely in garment industries and the demand for these products is increasing day by day due to their wear comfort characteristics 1 . The stretchable yarns are produced using core spinning technique on a modified ring frame, siro spinning, air entangling, hollow spindle spinning, rotor spinning and friction spinning 2-7 . Each system has its own features. The conventional ring spinning is simple and economical. Core-spun yarn is produced at ring frame by combining a continuous strand through the delivery rollers and the staple fibres through normal drafting arrangement. The component fed through the delivery rollers is usually known as the "core", and the other component is known as the "sheath" that forms the outer cover. The core may be of continuous filament yarn or of spun yarn. The modified ring spinning frame included a positive feed roller as elastane delivery unit and a V-groove guide to feed the elastane filament to front roller. The elastane filament is stretched between the positive feed roller and front roller, which will provide elasticity in core-spun yarn. The basic requirement to produce an elastic core-spun yarn is to stretch a spandex thread before it enters the spinning unit 8 . This action provides elasticity in the final yarn by retraction of the elastane core when stress is removed, thus compacting and bulking the spun yarn cover. The core-spun yarn can be extended to the point where the non-elastic sheath portion of the yarn is stretched to its limit, thus resisting further extension of the core-spun yarn 9 . Su et al. 10 studied the structural and performance characteristics of elastic core-spun yarns. They have produced 19.7 tex elastic core-spun yarn from 44.4 dtex/4f spandex filament as the core and cotton fibers as the sheath. In order to improve yarn performance, they examined the yams cross-sectional structure and investigated the effect of draw ratio and feed-in angle of the spandex on the structure and performance of yarn. Su et al. 11 used spandexes of three degrees of fineness as core material with cotton fibers as the sheath to spin fine elastomeric yarns. They have reported that the production of a finer elastomeric yarn with a uniform structure is feasible. Adeli et al. 12 carried out structural evaluations of elastic core-spun yarns and fabrics under tensile fatigue loading. They have measured the tensile properties of fatigued yarns by a tensile tester 3 and the work carries detailed study on mechanical characteristics of high elastic core-spun yarn made in rotor spinning with spandex as core. Miao et al. 13 stated that at a low pre-tension level the core filament could migrate from the centre to the outer layers and back to the centre repeatedly during core yarn —————— a Corresponding author. E-mail: apurba65@gmail.com