Crystallization Behavior of Homochiral Polymer in Poly(L-lactic acid)/Poly(D-lactic acid) Asymmetric Blends: Effect of Melting States

Blending of poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) leads to the formation of poly(lactide) stereocomplexation (PLA SC), which exhibits higher melting temperature and faster crystallization rate. The crystallization behavior of PLA homochiral crystallization (HC) under the existence of PLA SC was also widely investigated. During the variable processing, the SC with different morphologies would produce, and these SC could exert different influences on the subsequent formation of HC. However, the effects of SC developed in various conditions on the formation of HC are not compared yet and are also not clear until now, and which is important for the application of PLLA/PDLA blends. In this paper, the PDLAs with different molecular weights were blended with PLLA at a weight ratio of PLLA/PDLA 90/10, and the crystallization behaviors of PLLA HC from different conditions were investigated by differential scanning calorimetry (DSC). Results indicated that, incorporating a small amount of PDLA accelerated the formation of PLLA HC significantly regardless of the SC developed from the solution evaporation or the melt. The higher crystallization rate of HC was received in the PLLA/PDLA specimens with lower molecular weight of PDLA. For the specimens crystallized from the partially melting (most of SC developed during solution evaporation), the crystallization rate was higher than that corresponding specimens crystallized from the completely melting state (the SC were produced from the melt). This discrepancy would be due to variable SC morphologies produced during diverse processing.