Relation between neck-like deformation and fiber structure formation in high-speed melt spinning of ethylene terephthalate/ethnylene isophthalate copolymers.

Abstract

Four kinds of ethylene terephthalate/ethylene isophthalate copolymers (PET/PEI, PEI=0, 2, 5, 10mol%) were prepared and melt spun at take-up velocities from 1 to 7km/min. Birefringence and density of as-spun fibers increased with increasing take-up velocity. Density showed abrupt increase due to oriented crystallization at take-up velocities above 5km/min, where birefringence and density became lower for higher PEI contents. Radial variation of birefringence in filament cross-section measured with an interference microscope was also lower for the higher PET content fibers. Moreover, increase in PEI content caused the decrease in Young's modulus and tenacity and the increase in extension at break. These results suggest that development of fiber structure through the oriented crystallization was suppressed by the existence of the ethylene isophthalate component.Filament diameter profiles in the spinline were measured using a diameter monitor. Below 4km/min, filaments attenuated smoothly along the spinline, while above 5km/min, neck-like deformation was observed. With increasing PEI content, position of the neck-like deformation moved downward in the spinline, and necking draw ratio decreased. From the relation between the neck-like deformation in the spinline and the physical and mechanical properties of high-speed spun fibers, it is concluded that birefringence, density, Young's modulus, tenacity and extension at break of as-spun fibers are governed by the necking draw ratio, and that the radial variation of birefringence is governed by the position of neck-like deformation.