Studies on heating and cooling of synthetic fibers, yarns, and fabrics. I. Properties of nylon and polyester filament yarns on heat setting in silicone oil

Abstract

AbstractNylon 6, nylon 66, and polyester [poly(ethylene terephthalate)] filament yarns were heat set at different temperatures in oil under a variety of experimental conditions. The effect of time of heat setting, tension on the yarn during heat setting, as well as the effect of the initial tenacity and extension on subsequent changes in the mechanical properties of the heat‐set yarns have been studied. The breaking strength, elongation at break, and work of rupture have been found to be different for samples heat set while slack and at constant length. The breaking strength remains more or less constant over a wide range of heat setting temperatures up to 240°C in the case of nylon 66 and polyester, and up to 200°C in the case of nylon 6, contrary to the observations of Dumbleton et al. When treated in the slack condition, the breaking extension increases by about 1–2.5 times the control value, while heat setting at constant length produces a decrease in the case of nylon 66 and a marginal increase in the case of nylon 6 and polyester. The initial modulus decreases irrespective of the conditions under which the filaments are heat set. From measurements of the shrinkage and the residual shrinkage in boiling water it appears that dimensional stability can be achieved by heat setting even at constant length. Heat setting produces significant improvement in the crease recovery and resiliency of the fibers. Heat setting has also been found to significantly increase the overall crystallinity of the fibers as determined by critical dissolution time and parallel and perpendicular refractive indices. The overall orientation of the polymer chains, as determined from sonic velocity measurements, decreases on heat setting in the slack condition. Heat setting at constant length produces a marginal improvement in the overall orientation only in the case of nylon 66 yarns. Shrinkage occurs instantaneously. Crystallinity, on the other hand, improves with increasing time of heat setting.