Remarkably Enhanced Impact Toughness and Heat Resistance of poly(l-Lactide)/Thermoplastic Polyurethane Blends by Constructing Stereocomplex Crystallites in the Matrix

As an eco-friendly polymer with tremendous potential to replace traditional petroleum-based and nonbiodegradable polymers, the current use of poly(l-lactide) (PLLA) in large-scale commercial applications still faces some barriers mostly associated with its inherent brittleness and poor heat resistance. In this work, we propose a novel and facile strategy to simultaneously address these obstacles by introducing small amounts of poly(d-lactide) (PDLA) into thermoplastic polyurethane (TPU) toughened PLLA blends through melt-blending. The results manifest that the introduced PDLA chains can readily interact with PLLA matrix chains and rapidly cocrystallize into stereocomplex (sc) crystallites capable of acting as an efficient rheology modifier to dramatically improve melt viscoelasticity of the PLLA matrix and subsequently induce the morphological change of the dispersed TPU phase from a typical sea–island structure to a unique networklike structure, thus endowing PLLA/TPU/PDLA blends with remarkably improved impact toughness as compared to its PLLA/TPU counterparts. Moreover, the formed sc crystallites can also serve as a highly efficient nucleating agents to substantially accelerate matrix crystallization, which makes it possible to prepare PLLA/TPU blends with a highly crystalline matrix using conventional injection molding technology. More interestingly, the improvement in the matrix crystallization can significantly enhance the heat resistance of the blends without evidently weakening the contribution of the tailored phase morphology to the toughness improvement. These inspiring findings suggest that the construction of sc crystallites in the matrix could be a promising avenue toward fabricating high-performance PLLA/elastomer blends via simultaneously tuning phase morphology and matrix crystallization.