Crystal nucleation in random L/D-lactide copolymers
Crystal nucleation in random L/D-lactide copolymers
复制标题
DOI：
10.1016/j.eurpolymj.2016.01.020
复制
发表时间：
2016-02-01
影响因子：
6
通讯作者：
Schick, Christoph
中科院分区：
文献类型：
--
作者：
Androsch, Rene;Di Lorenzo, Maria Laura;Schick, Christoph
分析了聚 L-乳酸 (PLLA) 及其具有少量 D-异构体共单元但相同质均摩尔质量 120 kDa 的无规共聚物的非等温和等温结晶和成核行为。首先，证实总结晶速率和晶体生长速率随着链中D-异构体含量的增加而降低。延伸到早期的工作，结晶速率的等温分析是通过确定临界冷却速率来完成的，以抑制熔体的有序化。在 PLLA 均聚物的情况下，熔体需要比 0.5 K s(-1) 更快地冷却以抑制结晶，而在具有 4% D-异构体共单元的共聚物的情况下，临界冷却速率降低约一个数量级至 0.05 K s(-1)。然而，即使熔体的冷却速度快于抑制结晶的临界冷却速率，根据 D 异构体含量，在特定的冷却速率范围内仍然会发生成核，只有在比抑制结晶的临界冷却速率快两个数量级的冷却时才会停止。等温成核实验证实了在含有 D-异构体共单元的 PLLA 中在非等温条件下较慢成核的观察结果。 (C) 2016 Elsevier Ltd. 保留所有权利。
Poly (L-lactic acid) (PLLA) and its random copolymers with small amount of D-isomer co-units but identical mass-average molar mass of 120 kDa were analyzed regarding the non-isothermal and isothermal crystallization and nucleation behaviors. First, it was confirmed that the gross crystallization rate and crystal growth rate decrease with increasing D-isomer content in the chains. In extension to earlier work, the isothermal analysis of the crystallization rate was completed by determination of critical cooling rates to suppress ordering of the melt. While in case of the PLLA homopolymer the melt needs to be cooled faster than 0.5 K s(-1) in order to suppress crystallization, the critical cooling rate is lowered by about one order of magnitude to 0.05 K s(-1) in case of a copolymer with 4% D-isomer co-units. However, even if the melt is cooled faster than the critical cooling rate to suppress crystallization, nuclei formation still occurs in a specific cooling-rate range depending on the D-isomer content, ceasing only on cooling about two orders of magnitude faster than the critical cooling rate to suppress crystallization. The observation of slower nuclei formation at non-isothermal conditions in PLLA containing D-isomer co-units is confirmed by isothermal nucleation experiments. (C) 2016 Elsevier Ltd. All rights reserved.