The high-speed melt spinning of poly(ethylene 2,6-naphthalene dicarboxylate ) ( PEN ) was performed up to the take-up velocity of the ultra-high-speed region, 9 km/min. From the investigations of the structure and physical properties of the asspun fibers, the high-speed spinning of PEN was divided into three regions in terms of the mechanism of fiber 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 velocity of 2.5-4.5 km/min and the birefringence of 0.08 -0.25, although some experimental evidences indicated that the orientation-induced crystallization did not occur, there was an increase in the fiber density which suggested the formation of some ordered structure. At the take-up velocity ú 4.5 km/min and birefringence ú 0.25, the orientation-induced crystallization occurred. The fibers obtained in this region were characterized by the formation of the crystalline structure dominated by the b form. The presence of the necklike deformation in the spinning line was also confirmed. The solidification temperature of the spinning line analyzed from the diameter profile suggested that the formation of b modification crystals occurred at relatively low crystallization temperatures in comparison with that in an isotropic state. Therefore it was indicated that the presence of elongational stress in the spinning line promoted the formation of the b modification crystals.
Structure of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) fibers prepared by drawing and annealing processes has been analyzed through wide-angle X-ray diffraction (WAXD), density, infrared dichroism, and birefringence measurements. There are three different types of crystalline structure in these fibers: two of these are the two types of orthorhombic with different orientation modes (the ordinary c-axis orientation (cFZ), and the preferential orientation of c-axis to the direction perpendicular to the fiber axis (cЌZ)); and the third is pseudohexagonal. The weight fractions of the three types of crystals and amorphous phase were analyzed combining the WAXD integrated intensity and density data. The relation between crystalline orientation factors obtained separately from the WAXD measurement and the infrared dichroic ratio is also discussed. The birefringence of these fibers shows negative and positive values, depending on drawing and annealing temperatures. Considering the intrinsic birefringence and weight fraction of the cFZ, cЌZ, and pseudohexagonal crystals, birefringence of the amorphous phase was evaluated. The amorphous birefringence shows positive values and decreases with an increase in the annealing temperature. From the analyzed fiber structure, it was speculated that the cЌZ and pseudohexagonal crystals are preferentially formed in the drawing process irrespective of the drawing temperature.
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