Polyethylene oxide enhances the ductility and toughness of polylactic acid: the role of mesophase

Melt stretching and quenching produce low-crystalline biodegradable poly(lactic acid) filled with β-form shish for highly improved mechanical toughness

High-toughness biodegradable poly(lactic acid) (PLA) has always been intensively pursued on the way of replacing traditional petroleum-based plastics. Regulating microstructures to achieve self-toughening holds great promise due to avoidance of incorporating other heterogeneous components. Herein, we propose a straightforward and effective way to tailor microstructures and properties of PLA through melt-stretching and quenching of slightly crosslinked samples. The melt stretching drives chains orientation and crystallization at high temperature, while the quenching followed can freeze the crystallization process to any stage. For the first time, we prepare a type of transparent and low-crystalline PLA filled with rod-like β-form shish, which displays an outstanding tensile toughness, almost 17 times that of the conventional technique-processed one. This mechanical superiority is enabled by an integration of high ductility due to oriented chain network, and high tensile stress endowed by nanofibrous filler's role of β-form shish. Furthermore, the mechanically toughened PLA is demonstrated to generate the richest micro-cracks and shear bands under loading, which can effectively dissipate the deformational energy and underlie the high toughness. This work opens a new prospect for the bottom-up design of high-performance bio-based PLA materials that are tough, ductile and transparent by precise microstructural regulation through scalable melt processing route.

Enhancement of tensile toughness of poly(lactic acid) (PLA) through blending of a polydecalactone-grafted cellulose copolymer: The effect of mesophase transition on mechanical properties

Increasing the toughness of poly(lactic acid) (PLA), i.e., simultaneously increasing both the tensile strength and ductility, remains a major challenge. In this study, fully bio-based PLA blends with polydecalactone (PDL)-grafted cellulose copolymer (CgPD) were prepared and comprehensively analyzed to enhance the toughness of the PLA matrix. The blends were found by FT-IR and solid-state ¹H NMR to be physically intact and miscible at the sub-twenty-nanometer scale. The WXRD and DSC analyses indicated that the addition of the alkyl-branched CgPD imparts a more structurally disordered PLA mesophase state to the prepared PLA_CgPD bio-blends. UTM analysis was used to characterize the macroscopic mechanical properties of the PLA_CgPD bio-blends. Both the tensile strength and elongation properties were simultaneously improved with the addition of 1 wt% CgPD loading amount to PLA (PLA_CgPD1). This study experimentally demonstrates that the enhanced mechanical properties of PLA_CgPD1 are closely related to the existence of more ordered PLA mesophases induced by the introduction of an optimal amount of CgPD into the PLA matrix.