Structure Development of Polylactides with Various d-Lactide Contents in the High-Speed Melt Spinning Process

Abstract

High-speed melt spinning of polylactides with various d-lactide contents was carried out and the structure and properties of the as-spun fibers were investigated. The highest take-up velocities attained for polylactides with low, middle, and high d-lactide contents (PLA-L, PLA-M, and PLA-H) were 10, 9, and 8 km/min, respectively. Birefringence of as-spun fibers increased with an increase in the take-up velocity. Fibers obtained at high take-up velocities showed lower birefringence with an increase in the d-lactide content. Distinct crystalline reflections appeared in WAXD patterns of PLA-L and PLA-M fibers spun at 5 and 6 km/min and higher, respectively. The crystal modification was α-form. In DSC thermograms, because of the difference in crystallizability of polymers and the effect of molecular orientation on crystallization rate, cold crystallization was observed for the PLA-L fibers obtained in a low take-up velocity region, whereas in a high take-up velocity region it was observed for the PLA-M fibers. Crystallinity analyzed from DSC thermograms of PLA-L and PLA-M increased with an increase in the take-up velocity. PLA-L fibers showed significantly higher crystallinity than PLA-M fibers, whereas PLA-H fibers were found to be amorphous up to the highest take-up velocities attained. Mechanical properties of as-spun fibers increased with an increase in the take-up velocity. The highest initial Young's modulus and tenacity, which were for PLA-L fibers obtained at 10 km/min, were about 5.9 GPa and 570 MPa, respectively.