Achieving High-Ductile Polylactide Sheets with Inherent Strength via a Compact and Uniform Stress Conduction Network

Conventional methods for toughening polylactide (PLA), such as plasticization and blending with flexible components, are prone to cause large reduction in its strength and stiffness. The objective of this study was to highly increase the ductility of PLA sheets without compromising its strength and sustainable nature. A compact and uniform stress conduction network was constructed inside PLA based on the scaffold-network nuclei from entanglement network of long chain branched-PLA, which dramatically increased the elongation at break from 8 to 229% and simultaneously enhanced the yield strength by 5% than normal PLA. Preorientation and homogeneity of PLA melts through layer-multiplying elements are indispensable for the growth of a compact and uniform network-like precursor from the scaffold-network nuclei. The existence of a network-like precursor was also implied from the observation of a network-like crystal by scanning electron microscopy (SEM) after the dynamic dissolution-crystallization process during high-temperature etching treatment. The toughening mechanism was proposed based on the stress transfer of the network-like precursor as a stress-conducting network and evidenced by the deformation of the network-like precursor as shown in the SEM images. The microfibrillation and microsized voids formed during deformation also largely promoted the energy consumption in tensile tests. This work brings new insights into the field of PLA toughening with sustained good strength and stiffness of original materials under the processing conditions of normal draw ratios.