Effect of thermal annealing on crystal evolution and multiple melting behaviors of molded poly(L-lactic acid) and poly(butylene succinate) blends upon heating investigated by TMDSC

The influence of post-process annealing treatment on the structural and thermal behaviors of poly(L-lactic acid)/poly(butylene succinate) (PLLA/PBS) blend was investigated by temperature modulated differential scanning calorimetry (TMDSC) and wide-angle X-ray diffractometry. It is shown that the low-order α′-structure of PLLA was formed in the as-molded samples and the molded products annealed at the temperatures below the melting of PBS, whereas the high-order α-crystal was developed when the high temperature of annealing (152 °C) was applied. With the addition of poly(ethylene glycol) plasticizer to the blends, the formation of high-order α-structure was prohibited. During the DSC heating scan, the α′- to α-crystalline phase transformation did not occur. The evidence of multiple melting behaviors observed by TMDSC was ascribed to the simultaneous melting, recrystallization, and remelting of the PLLA and PBS crystals in the blends.