College of Polymer Science and Engineering, Sichuan University, State Key Laboratory of Polymer Materials Engineering, Chengdu, 610065, Sichuan, China.
J Phys Chem B. 2013 Apr 4;117(13):3667-74. doi: 10.1021/jp311878f. Epub 2013 Mar 22.
The crystallization and melting behaviors and crystalline structure of melt and cold crystallized poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blend were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), respectively. The isothermal crystallization kinetics during the melt and cold crystallization process were analyzed using the Avrami equation. The overall crystallization rate constant (k) of cold crystallization is much higher than that of melt crystallization. Moreover, k as a function of crystallization temperature shows different trends in melt and cold crystallization, indicating different crystallization mechanisms in the melt and cold crystallization. The polymorphic crystallization of homocrystallites (the transition crystallization temperature from δ to α form) is not altered by either the equimolar blending of PLLA and PDLA or the type of crystallization procedures, while the crystallization window for exclusive stereocomplex crystallites is widened from 170 °C for melt crystallization to 170-200 °C for cold crystallization. The stereocomplex crystallites are hard to form in both melt and cold crystallization at crystallization temperatures of 90 and 100 °C, and the crystallinity of stereocomplex crystallites for cold crystallization is higher than that of melt crystallization at temperatures above 110 °C. Especially, a pure and significantly higher crystallinity of stereocomplex crystallites can be achieved at 170-200 °C by cold crystallization. The results provide a huge possibility to control stereocomplex crystallization to enlarge its applications.
采用差示扫描量热法（DSC）和广角 X 射线衍射（WAXD）分别研究了熔融和冷结晶聚（L-丙交酯）/聚（D-丙交酯）（PLLA/PDLA）共混物的结晶和熔融行为及晶体结构。采用 Avrami 方程分析了熔融和冷结晶过程中的等温结晶动力学。冷结晶的总结晶速率常数（k）远高于熔融结晶。此外，k 作为结晶温度的函数在熔融和冷结晶中表现出不同的趋势，表明在熔融和冷结晶中存在不同的结晶机制。同晶（从 δ 相到 α 相的转变结晶温度）的多晶结晶不受 PLLA 和 PDLA 等摩尔共混或结晶程序类型的影响，而专立体复合物结晶的结晶窗口从熔融结晶的 170°C 拓宽到 170-200°C 。在结晶温度为 90 和 100°C 的熔融和冷结晶中，立体复合物结晶都难以形成，并且在高于 110°C 的温度下，冷结晶的立体复合物结晶的结晶度高于熔融结晶。特别是，在 170-200°C 下通过冷结晶可以获得纯的和显著更高的立体复合物结晶度。结果为控制立体复合物结晶以扩大其应用提供了巨大的可能性。
