FIBER STRUCTURE FORMATION IN ULTRA-HIGH-SPEED MELT-SPINNING OF POLY(ETHYLENE 2,6-NAPHTHALENE DICARBOXYLATE)

The high-speed melt spinning of poly( ethylene 2,6-naphthalene dicarbo xylate) (PEN) was performed up to the take-up velocity of the ultra-hi gh-speed region, 9 km/min. From the investigations of the structure an d physical properties of the as-spun fibers, the high-speed spinning o f PEN was divided into three regions in terms of the mechanism of fibe r structure formation. The first region is the take-up velocity of up to 2.5 km/min and the birefringence of up to 0.08 where only a slight increase in molecular orientation was attained. At the take-up velocit y of 2.5-4.5 km/min and the birefringence of 0.08-0.25, although some experimental evidences indicated that the orientation-induced crystall ization did not occur, there was an increase in the fiber density whic h suggested the formation of some ordered structure. At the take-up ve locity > 4.5 km/min and birefringence > 0.25, the orientation-induced crystallization occurred. The fibers obtained in this region were char acterized by the formation of the crystalline structure dominated by t he beta form. The presence of the necklike deformation in the spinning line was also confirmed. The solidification temperature of the spinni ng line analyzed from the diameter profile suggested that the formatio n of beta modification crystals occurred at relatively low crystalliza tion temperatures in comparison with that in an isotropic state. There fore it was indicated that the presence of elongational stress in the spinning line promoted the formation of the beta modification crystals . (C) 1997 John Wiley & Sons, Inc.