Abstract
The present study intends to explore the mechanism of the structure formation in the ultra-high speed spinning of poly (ethylene 2, 6-naphthalenedicarboxylate) (PEN) fiber. PEN fibers were spun with spinning speeds in the range from 5000 to 8000m/min, and characterized in terms of their physical properties, thermal properties, and fiber structure. The results were compared with the fiber spun at 5000m/min which had been studied in previous papers. The increase in spinning speed over 5000m/min resulted in the further development of molecular orientation, producing the PEN fiber with high tenacity, low elongation, and low shrinkage. The tenacity reached the maximum value of 0.92 GPa at 7000m/min. This value seems to be the highest obtained by a simple high speed spinning of commercially available polymers. However, the tenacity decreased where the spinning speed exceeded 7000m/min, probably due to the formation of a skin-core structure. The crystallinity estimated by the wide angle X-ray scattering was considerably higher than that calculated from density, which suggests that a tight para-crystalline structure is formed during spinning. The β-form crystalline structure became more stable at higher spinning speeds, and the crystalline transition from β-form to α-form took place only partly by annealing as-spun fibers. A necking deformation was observed on the spin-line, as in other polyester fibers. The refractional interference patterns around the neck suggest the formation of a skin-core structure.
