Facile and efficient formation of stereocomplex polylactide fibers drawn at low temperatures

Abstract

Stereocomplex polylactide (SC-PLA) provides an effective route to improve heat-resistance through the formation of SC-PLA crystallites driven by hydrogen bonding interactions between poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA). Great progress has been made in low molecular-weight SC-PLA compounds. However, the development of strategies for exclusive stereocomplexation in high molecular-weight (high-MW) PLLA/PDLA racemic blends quenched from isotropic melt remains challenging. In this study, in-situ reactive melt-spinning of commercially available high-MW PLLA/PDLA blend with a new transesterification catalyst (i.e., sodium octanoate in MB) was devised as an effective strategy to prepare blends containing stereo-block PLA (sb-PLA) copolymers. As a result, the sb-PLA copolymers restricted phase separation and further promoted relatively weak CH3⋯ OC hydrogen bonding interactions, along with the development of the exclusive SC-PLA crystallites with low crystalline thickness (Lc) in PLLA/PDLA/MB blend fibers drawn at low temperatures (≤102 °C). In contrast, extremely limited transesterification reaction in PLLA/PDLA melt led to the phase separation and the resultant separate domains of PLLA or PDLA restricted the occurrence of the CH3⋯ OC hydrogen bonding interactions in the PLLA/PDLA blend fibers drawn at low temperatures (≤120 °C). Only when the PLLA/PDLA blend fibers were drawn at a high temperature (198 °C), the strong CH3⋯ OC hydrogen bonding interactions could be formed, along with the formation of the exclusive SC-PLA crystallites with high Lc. These findings provide a facile and effective strategy to develop industrial-scale PLA fibers containing the exclusive SC-PLA crystallites with improved heat-resistance.