多臂聚乳酸对线型聚乳酸结晶的促进作用

以多端羟基聚酯为引发剂，经丙交酯开环聚合得到多臂聚乳酸（MA-PLA）。 MA-PLA在DSC二次升温过程中，出现明显的冷结晶峰(41.5 J/g)和熔融峰(42.5 J/g)，而工业产品聚乳酸PLLA 3051D没有这2个峰，确认该多臂聚乳酸的结晶能力优于3051D。 MA-PLA多臂聚乳酸的左旋乳酸单元含量为97%，高于3051D的91%。 将MA-PLA与PLLA-3051D共混后，在DSC二次升温过程中出现了熔融峰和冷结晶峰。 偏光显微镜观察表明，共混物的成核速率和初期球晶生长速度加快。 等温结晶动力学数据表明，110 ℃等温结晶的半结晶时间由空白样品的53.6 min缩短至共混物的31.7 min，Avrami指数n由空白样品的2.25增加至共混物的2.60，可见多臂聚乳酸对线形聚乳酸结晶性能的改善，主要是加快了成核速率。

Promotion of Crystallization in Linear Polylactide by Multiarm-polylactide

Multi-arm polylactide(MA-PLA) was melt-blended with commercial polylactide(PLLA) to improve its crystallinity. MA-PLA was prepared by the ring-opening polymerization of L-lactide using multi-hydroxy-terminated polyester as initiator. The DSC curve during the 2nd heating shows an apparent cold crystallization peak(41.5 J/g) and a melting peak(42.5 J/g) for MA-PLA, which could not be observed for commercial PLLA 3051D and indicated a better crystallinity of MA-PLA than that of 3051D. The L-lactic acid unit content in MA-PLA was 97% and was higher than that in 3051D(91%). After blending with 6% MA-PLA, the blend showed an obvious cold crystallization peak and a melting peak. Polarized optical microscopy(POM) observation revealed a faster nucleation rate and an early stage spherulite growth rate in the blend than those in neat 3051D. The isothermal crystallization gave a half crystallization time of 53.6 min for neat 3051D and 31.7 min for the blend. In addition, the Avrami indexes(n) are 2.25 and 2.60 for 3051D and the blend respectively. The improvement in crystallinity was ascribed to the heterophase nucleation effect caused by the multi-arm polylactide.