Improving Flexibility of Poly(L-lactide) by Blending with Poly(L-lactic acid) Based Poly(ester-urethane): Morphology, Mechanical Properties, and Crystallization Behaviors

Poly(L-lactide) (PLLA) is one of the most promising biobased and biodegradable polymers. However, the lack of toughness restricts its application considerably. In the present study, PLLA was successfully toughened by blending with a poly(lactic acid) based poly(ester-urethane) (PEU), which contained poly(butylene succinate) as a flexible segment. The tensile properties and notched Izod impact strength of PLLA and toughened PLLA were investigated. The flexibility of PLLA was considerably improved after introduction of PEU by the evidence of high strain and improved impact strength. The crystallization behavior was investigated by differential scanning calorimeter (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). The glass transition temperature of toughened PLLA decreased with an increasing content of PEU, suggesting that the blends showed limited miscibility. POM observation showed that the crystallites of PEU uniformly distributed in the PLLA matrix after two-step crystallization at 120 and 60 degrees C. The results of WAXD suggest that the crystal structure of PLLA remained unchanged after blending with the PEU.