Analysis on Fiber Formation Behavior During High-speed In-line Drawing Process of Poly

Abstract

High-speed in-line drawing process, in which melt spinning and drawing processes are connected, is one of the most widely used processes for production of commodity fibers. In this study, on-line measurements of diameter, velocity and birefringence were conducted in the high-speed in-line drawing process of poly(ethylene terephthalate) (PET). Filament started to deform immediately after passing through the first godet roller. The maximum strain rate under the drawing condition of from 2 to 4 km/min reached a high value of 510 s-1. Birefringence of filament increased steeply in this region. Comparison of orientation development during melt spinning and drawing processes revealed that the birefringence measured in the high-speed spinning line showed lower values than that in the in-line drawing line at the same diameter. Structure evolution of in-line drawn filament prepared under various processing conditions was investigated through off-line measurements of wide-angle X-ray diffraction (WAXD), birefringence, and density. Although drawing temperature was slightly higher than the glass transition temperature (Tg) of PET, significant development of oriented mesophase was confirmed. At the same time, a sharp meridional (001’) peak, which is reported to be originated from well-ordered smectic-C phase, also was clearly observed. In-situ measurement of WAXD pattern during heating process of highly drawn filament revealed that the intensity of (001’) peak started to increase gradually below Tg and started to decrease above Tg. Along with the reduction of the intensity of (001’), crystalline reflections of ordinary triclinic crystal started to appear above Tg, indicating that the mesophase acts as a transitional precursor for crystallization.