Mechanically rejuvenated glassy polylactide with spatial heterogeneity and packing efficiency: Time dependence of deformation behavior

Abstract

Mechanical rejuvenation is effective in conquering the physical aging of polymers, but its molecular origin is far from clear. Herein, glassy polylactide is subjected to mechanical rejuvenation under extensional stress field via “casting-thermal stretching”, and the joint effect of spatial heterogeneity and packing efficiency on the brittle-to-ductile transition is demonstrated. The extensional stress accelerates segmental relaxation and heavily enhances the spatial heterogeneity in activated amorphous fraction. The much larger extensional stress enhances the orientation and packing efficiency of polylactide chains, with the close-packing amorphous fraction restraining the molecular mobility but boosting self-reinforcement. Strong time-dependent deformation behavior is discovered in rejuvenated polylactide, with different draw ratios exhibiting quite different critical strain rates of ductile-to-brittle transition, and that with densified network even maintains high ductility at extremely high strain rate. This work provides new insights into mechanical rejuvenation and significant guidance for the processing of advanced biodegradable polymers.