Effect of Extraordinary Large Diameter Nozzle in High-speed Melt Spinning of Poly(ethylene terephthalate).

Abstract

High-speed melt spinning of poly (ethylene terephthalate) was performed using a nozzle with extraordinary large diameter of 5mm. A metallic porous filter was set in the nozzle to maintain high extrusion pressure. The structure of the as-spun fibers was compared with the fibers prepared using an ordinary nozzle. The molecular orientation of fibers spun at low take-up velocities, where orientation-induced crystallization did not take place, increrased by enlarging the nozzle diameter. The orientation-induced crystallization started at lower take-up velocities because of enhanced molecular orientation. On the other hand, the structure of crystallized fibers obtained at high take-up velocities was characterized by high crystallinity and relatively low molecular orientation. The on-line measurement of spinline velocity for the take-up velocity of 5km/min revealed that, in comparison with the spinning with ordinary nozzle, the spinline velocity increased more steeply near the spinneret and the solidification of the spinline occurred at a position closer to the spinneret. The solidification temperature, i. e. the crystallization temperature, estimated from the measured velocity profile also increased by enlarging the nozzle diameter. These changes were attributed to increase in temperature difference between center and surface of the spinline, which might lead to the stress concentration and the promotion of orientation-induced crystallization in the skin layer.