Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating.

Shyr Shyr,Ko Ko,Chen Chen

doi:10.3390/polym11091502

Shyr Shyr, Ko Ko + Show 1 more

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https://doi.org/10.3390/polym11091502

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Journal: Polymers	Publication Date: Sep 14, 2019
Citations: 6	License type: CC BY 4.0

Affiliation: Feng Chia University, National Tsing Hua University

Abstract

A series of poly(l-lactide)/poly(d-lactide) blended chips (LDC), as-spun LD fibers (LDA) and hot-drawn LD fibers (LDH) were prepared for investigating the homocrystallization and stereocomplex crystallization behaviors of LDA and LDH fibers during heating. Modulated differential scanning calorimetry (MDSC), hot stage polarized microscopy (HSPM), and real-time wide-angle X-ray diffraction (WAXD) were used for studying the crystallization and melting behaviors, fiber morphology, and crystalline structure evolution of the LDA and LDH fibers’ homocrystals and stereocomplex crystals during heating. The molecular chain orientations of the LDA and LDH fibers were obtained through spinning and improved through the hot drawing processes. When the molecular chain was oriented on the fiber axis, the homocrystals and stereocomplex crystals of the fibers began to form in turn as the heating temperature exceeded the glass transition temperature of the fiber. The side-by-side packing of the molecular chains was promoted by mixing the molecular chains with the extrusion screw during the spinning process, facilitating stereocomplex crystallization. When the LDA fiber was heated above the glass transition temperature of the fiber, movement of the fiber molecular chain—including molecular chain orientation and relaxation, as well as crystallization, melting, and recrystallization of homocrystals and stereocomplex crystals—were investigated through HSPM. MDSC and real-time WAXD were used to observe the molecular chains of the melted poly(l-lactide) and poly(d-lactide) homocrystals of the fibers rearranging and transiting to form stereocomplex crystals during heating.

Highlights

Polylactide (PLA) is an aliphatic polyester with excellent biocompatibility and biodegradability.Monomer, lactic acid exists in two enantiomeric forms: l-lactic acid and d-lactic acid
The results demonstrate that stereocomplex crystallization of L5DH was almost the same as that of L5DA
A series of the LD chips, as-spun fibers, and hot-drawn fibers were prepared for studying homocrystallization and stereocomplex crystallization during heating

Summary

Introduction

Polylactide (PLA) is an aliphatic polyester with excellent biocompatibility and biodegradability. Even in the PLLA/PDLA blended fibers, the annealing forms a fiber consisting mainly of highly oriented stereocomplex crystals. Annealing of the drawn fibers at an elevated temperature higher than the melting temperature of homocrystals increases the stereocomplex crystal content significantly. Some of the drawn fibers exhibit very broad wide-angle X-ray diffraction (WAXD) reflections from the homocrystals, which immediately transform to stereocomplex crystals in the annealing process at elevated temperatures without relaxing the molecular orientation of PLLA and PDLA. Xiuqin Zhang et al [13] show that highly oriented stereocomplex crystals can be formed in PLLA/PDLA blend fibers drawn at 60 ◦ C and annealed at 200 ◦ C. For PLLA/PDLA blend fibers drawn twice at 60 ◦ C, the crystallinity of stereocomplex crystals increases with annealing temperature in the range of 200 to 215 ◦ C, while the degree of orientation decreases slightly. The movement of the fiber molecular chains and the molecular chain rearrangement and transformation of the molten PLLA and PDLA to form stereocomplex crystals were discussed in this work

Materials and Methods

Discussion

Due α transition transition in

Polarized photographs of the Markers as‐spun H

Conclusions