writer：Shouyu Chen, Yaqiong Zhang, Huagao Fang, Yunsheng Ding and Zhigang Wang
keywords：聚乳酸，球晶，玻璃化转变，生长速度
source：期刊
specific source：CrystEngComm, 2013,15, 5464-5475
Issue time：2013年

Isothermal crystallization processes in the temperature range from 110 to 140 °C were studied by using polarizing optical microscopy (POM) for poly(L-lactide) (PLLA) film samples with and without confinement conditions. The PLLA film samples were prepared by melt pressing between two cover glasses to provide the surface confinements and by removing the top cover glasses or by solution cast to keep the top surface free of confinements, respectively. Through carefully following the changes of spherulite radius with crystallization time, it is surprisingly found that there exists an acceleration of spherulitic growth rates at the late stage following the normal spherulitic growth rates at the early stage of isothermal crystallization for PLLA film samples with both surface confinement (by cover glasses) and planar confinement conditions (by aggregation of adjacent spherulites to form “lake-like” regions) at certain temperatures, while the spherulitic growth rates remain constant at each isothermal crystallization temperature for PLLA film samples without the confinement conditions. On the basis of data analyses on the spherulitic growth rates under various conditions from several different aspects, it is finally concluded that the decreases of glass transition temperature induced by crystallization under confinement conditions during isothermal crystallization of PLLA film samples cause the peculiar spherulitic growth rate acceleration at the late stage.

摘要：本文通过偏光显微镜法（POM）研究了聚乳酸（PLLA）样品在110-140^oC温度范围内的等温结晶过程。PLLA样品分别通过两种方法制备：熔融热压法制备表面受限样品；融压后揭去一个玻片或溶液滴膜法制备非表面受限样品。通过仔细测试PLLA结晶过程中球晶半径随时间的变化关系，惊奇地发现，PLLA在某些温度下等温结晶后期存在球晶生长加速的现象，此时过冷非晶区PLLA样品同时存在表面受限（玻片覆盖）和平面受限（相邻球晶相互碰撞形成一定的“lake-like”区域），但是非表面受限样品以及只存在表面受限的样品在结晶过程中球晶生长速率则保持恒定。通过从多方面对实验数据进行解析后，发现是等温结晶过程中受限非晶区过冷熔体玻璃化温度降低导致了结晶后期球晶生长速率加速现象的出现。