Superior properties such as high strength, toughness and transparency of fully biobased poly(lactide) (PLA) were achieved simultaneously without any external modifiers. The improvement in properties is well explained by a structural/morphological study. Stereocomplex PLA (SC-PLA) was obtained by melt compounding asymmetric poly(Llactide)/poly(D-lactide) (PLLA/PDLA) blends at 200°C and confirmed by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) analyses. The SC-PLA domains (d = 950−1200 nm) lead to a physical cross-link network in the PLLA matrix. Rheology and Molau experiment reveal two different microstructures as a function of SC-PLA content, i.e., the connection of SC-PLA domains varied from chain entanglement to direct molecular bridging when the SC-PLA content increased from 10% to 23%. The SC-PLA crystals and the cross-link network reinforced the PLLA matrix, resulting in increases in melt viscosity, modulus and yield strength. Surprisingly, the elongation at break of the PLLA/PDLA blends was increased concomitantly from 11% to 200% with the SC-PLA content up to 10%. The brittle-to-ductile transition is ascribed to the cross-link network and easy deformation/cavitation of the SC-PLA domains. In addition, the asymmetric PLLA/PDLA blends exhibit an average visible light transmittance as high as 70% and the blends showed excellent heat-resistance after a short annealing at 100°C.

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Poly(lactide), PLA, as one of the most promising biopolymers, has been receiving increasing attention in recent years because of its excellent performances in renewability, mechanical properties, biocompatibility and biodegradability. However, its application is limited by its brittleness and low heat distortion temperatures (HDT). The low HDT mainly results from a low crystallization rate and lack of crystallinity after fast processing, e.g. injection molding. Consequently, considerable attention was paid, in recent years, to achieve fast(er) crystallization of PLA. In here, we briefly review the research progress in the crystallization modification of PLA notably by means of adding nucleating agents and stereocomplexation.

Crystallization kinetics of poly (lactide) were enhanced by using oxalamide compounds as nucleators and the nucleation efficiency can be well tailored by tuning the aliphatic spacer length between the oxalamide moieties.

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