Achieving morphological evolution and interfacial enhancement in fully degradable and supertough polylactide/polyurethane elastomer blends by interfacial stereocomplexation

The degradable polyurethane elastomers containing poly (L-lactide) (L-PU) and poly (D-lactide) (D-PU) were synthesized and incorporated in commercial PLLA as the toughening modifier. The stereocomplexation of PLA (sc-PLA) is successfully achieved at the interface of PU and PLLA domains in a single melt-blending process. The morphology and matrix crystallization in PLLA/D-PU blends is significantly improved by the presence of interfacial sc-PLA, showing morphological evolution to strip-shaped dispersion of PU phase and remarkable acceleration in matrix crystallization kinetics. After incorporating D-PU, the mechanical properties of blends are improved by interfacial sc-PLA, demonstrating that the notched Izod impact strength increases from 11.8 ± 3.1 KJ/m2 of PLLA/L-PU15 to 27.0 ± 5.8 KJ/m2 of PLLA/D-PU15 and even greater enhancement after thermal annealing is achieved. By observing the morphology of the impact fracture surface, the toughening mechanism of D-PU is investigated, revealing that the superior interfacial strength facilitates shear yielding of non-annealed sample and further prohibits de-bonding of rubber phase after thermal annealing. Hydrolysis tests in alkaline environment show that although interfacial sc-PLA can retard the hydrolysis rate, the blends still experience rapid weight loss to achieve full degradation. This work provides a highly effective strategy to toughen PLLA without sacrificing its degradability.