Structure and Mechanical Properties of Poly(trimethylene terephthalate) Fibers Obtained by CO_2 Laser Drawing and a Secondary Contact Heater Drawing

摘要

CO_2 laser drawing heats a running fiber homogeneously and rapidly without contact by laser irradiation and develops a necking in a fixed location. As-spun fibers of bio- and chemo-based poly(trimethylene terephthalate) (PTT) were drawn to draw ratio (DR) of 3.5-5.5 and 3.5-4.8 by CO_2 laser-heated drawing, respectively, which was taken as the first drawing. Secondarily the first-drawn fibers were drawn to total draw ratio (TDR) as high as possible by direct contact heater drawing of 150℃, which attained TDR 5.60-5.70 and 5.40-5.46 for bio- and chemo-based PTT fibers, respectively. Drawing stress in situ measured in the two-steps drawing increased roughly proportional to draw ratio, and for bio-based PTT was higher than for chemo-based one when compared at the same DR and TDR. We investigated in this study the structure and mechanical properties of the drawn PTT fibers by wide angle X-ray diffraction (WAXD), birernngence, thermo-mechanical property, and tensile property. The typical WAXD pattern of PTT crystal was observed with orientation-induced crystallization by the two-steps drawing. But, the meridional reflections become blurred and their intensities decrease with increasing draw ratio and by the second drawing. The transverse crystallite sizes, along the normal direction of (010) plane, increased transversely but the longitudinal sizes, along the normal direction of (002) plane decreased longitudinally as draw ratio increased for chemo-based PTT, whereas for bio-based PTT, the crystallite size change with draw ratio was the same trend with the chemo-based by the first drawing but the crystallite became much smaller transversely and longitudinally by the second drawing. By the azimuthal intensity profile, the crystal orientation factor obtained from (010) plane increased, while that from (002) plane decreased with the total draw ratio. The birefringence was a constant value 0.07 with no dependence on draw ratio by two steps drawing, which is over twice a reported intrinsic birernngence of PTT crystal, 0.029 [12]. Also, Young's modulus held an almost constant value of 2.3-2.6 GPa by the two stages drawing, which is very closed to 2.59 GPa, the theoretical modulus of PTT crystal.