Control of High-order Structure of Poly(ethylene terephthalate) Fibers by Blending with Liquid Crystalline Polymer

Abstract

Poly(ethylene terephthalate) (PET) fibers blended with a small amount of liquid crystalline polymer (LCP) were prepared by melt spinning at take-up velocities of 0.5, 2 and 4 km/min. Structure and properties of the fibers were analyzed by measurements of wide-angle X-ray diffraction, birefringence, modulated differential scanning calorimetry, scanning electron microscopy and mechanical properties. The experimental results clearly showed that the blending with LCP had no significant effect on the high-order structure of PET fibers at low take-up velocities, whereas molecular orientation and orientation-induced crystallization were significantly suppressed at high velocities. Mixing conditions also affected the structure development of PET component, in that the increase in the revolution frequency of screw resulted in the decrease of the effect of LCP for suppressing the orientation-induced crystallization. In the drawing of as-spun PET/LCP blend fibers, high drawing temperatures prevented the breakage of the fibers at high draw ratios and led to the preparation of drawn fibers with high tensile modulus and strength of 123 cN/dtex (17GPa) and 9.4 cN/dtex (1.3 GPa), respectively.

Structure Development in the Melt Spinning of Polypropylene/Ethylene Butene Copolymer Blends and Birefringence Suppression Effect

“…4 shows that small amount of PP could largely decrease the birefringence of the PP/EBM blend fibers. The similar phenomenon was also reported with other polymer pairs (Min et al, 1984;Endo et al, 1986;Brody, 1986;Ohkoshi et al, 1992;Kikutani et al, 1995;Yu and White, 1999;Yoshimura et al, 2002;Kojima and Kikutani, 2005). For personal use only.…”

“…Yoshimura (2002) reported that 2 wt.% of polymethyl methacrylate (PMMA) could decrease the birefringence of PET fibers. Kojima and Kikutani (2005) reported 5 wt.% of liquid crystalline polymer could also decrease the birefringence of PET fibers. So far, there is no widely accepted explanation to these phenomena.…”

“…In the 1980s, this effort interacted with the growing efforts to understand polymer blends. Studies of melt spinning of polymer blends were reported by various investigators (Min, 1984;Endo et al, 1986;Brody, 1986;Ohkoshi et al, 1992;Kikutani et al, 1995;Yu and White, 1999;Yoshimura et al, 2002;Kojima and Kikutani, 2005). In these studies, it was often found that the fiber birefringence of one polymer could be greatly suppressed by adding 3 to 20 wt.% of another polymer.…”

Molecular orientation of extruded PET/LCP blend films. II. X‐ray pole figures

“…In fibers of PET/LCP blends prepared by melt spinning, 12,26,27 no significant effect of the LCP on the high-order structure of the PET at low take-up velocities were found, while molecular orientation and orientation-induced crystallization were considerably suppressed at high velocities. X-ray studies of extruded sheets of PET, LCP, and their blends 12 showed a high degree of orientation along the extrusion direction. The orientation was mainly due to the crystallization rate of the matrix, although adding LCP could also induce crystallization and orientation of the PET in the blends.…”

“…12,13,18,[23][24][25][26][27][28][29][30][31][32][33][34][35][36] In general, these studies demonstrated that the mechanical properties of the blends are significantly affected by the mode of dispersion, shape, and orientation of the LCP and the interfacial interactions between the two phases. In some cases, significant improvement in strength and stiffness are found.…”