Zhang Xin, Yang Biao, Fan Baomin, Sun Hui, Zhang Huijuan
College of Chemistry and Materials Engineering, Beijing Technology and Business University, Beijing 100048, P. R. China.
ACS Macro Lett. 2021 Jan 19;10(1):154-160. doi: 10.1021/acsmacrolett.0c00830. Epub 2021 Jan 7.
We report on enhancing crystallization and heat resistance of poly(l-lactic acid) (PLLA) by d-sorbitol as a small molecule nucleating agent via melt blending. During the reheating process, the cold crystallization disappeared and the crystallinity of nucleated PLLA exceeded 50%. The heat deflection temperature of PLLA was elevated from 56 to 132 °C by simply increasing the mold temperature (90 °C) without an additional annealing treatment. We also observed the polymorphic crystals of PLLA during melt crystallization, i.e., the coexistence of hexagonal and lenticular crystals, along with their various geometrical aggregates in addition to plenty of conventional spherulites. On the basis of the fact that the nonisothermal crystallization temperature of PLLA (110 °C at a cooling rate of 10 °C/min) was higher than the melting point of d-sorbitol (about 93 °C), we speculated that d-sorbitol promoted the crystallization of PLLA through a homogeneous nucleation mechanism.
我们报道了通过熔融共混，将d-山梨醇作为小分子成核剂来提高聚（L-乳酸）（PLLA）的结晶度和耐热性。在再加热过程中，冷结晶消失，成核PLLA的结晶度超过50%。通过简单提高模具温度（90°C），无需额外的退火处理，PLLA的热变形温度从56°C提高到了132°C。我们还观察到了PLLA在熔融结晶过程中的多晶型晶体，即六方晶体和透镜状晶体共存，除了大量常规球晶外，还有它们的各种几何聚集体。基于PLLA的非等温结晶温度（在10°C/min的冷却速率下为110°C）高于d-山梨醇的熔点（约93°C）这一事实，我们推测d-山梨醇通过均相成核机制促进了PLLA的结晶。
