The Internal Structure of Sheath Fibre in DREF-3 Yarn

This paper is concerned with a study of the structure and twisting mechanism of sheath fibres in DREF-3 yarn, in which a tracer-fibre technique was used. The yarn was made from a polypropylene-fibre multifilament core and cotton staple-fibre sheath. An analysis of the twist and migration behaviour of the sheath is made to quantify the sheath structure. Process variables investigated are the spinning-drum speed, the yarn-delivery rate, and the surface structure of the core component. Other process variables, e.g. the suction pressure, yarn count, core-sheath ratio, and number of wrapper slivers, are kept constant. The effects on the sheath structure (quantified as the total twist, twist distribution, and migration behaviour) of certain process variables are discussed and possible causative factors identified. Conclusions arising from these in addition to visual observation of the sheath structure are used to explain the twisting mechanism of sheath fibres in DREF-3 yarn. An attempt is also made to explain the yarn properties for various process parameters on the basis of the sheath structure.