Effect of Molecular Chain Mobility Induced by High-Pressure CO2 on Crystallization Memory Behavior of Poly(D-lactic Acid)

Recently, the homogeneous crystallization of polymers under CO2 has been investigated systematically, while the effect of CO2 on heterogeneous crystallization such as crystallization memory effect of poly(lactic acid) (PLA) is still unknown due to its complicated process. In this study, the crystallization behavior induced by the crystallization memory effect of poly(D-lactic acid) (PDLA) under CO2 has been studied. The results showed that the crystallization memory effect decreased the difference in nucleation kinetics between PLA under the atmosphere and CO2 and the secondary nucleation constant increased with increasing CO2. Except for kinetics, the crystallization morphology was affected by CO2. During the crystallization memory process, the existence of CO2 activated the molecular chain mobility and affected the structure of both the original central spherulite and the newly formed spherulites. The plasticization effect of CO2 prevented the branching of the original central spherulite, and with the help of the residue molecular chain, the height of the central spherulite increased. The dendritic crystals at the periphery of the growth front of the central spherulite changed to rod-like crystals due to the increasing chain diffusion and the closer chain arrangement caused by CO2. As a result, the perfection of both central spherulites and newly formed spherulites was increased by CO2. This study reveals that the increasing chain mobility under CO2 changes crystallization morphology of both recrystallized spherulites and newly formed spherulites and benefits the formation of more perfect crystals.

Automated summary

This study explores the crystallization behavior induced by the crystallization memory effect of poly(D-lactic acid) (PDLA) under CO2. The results show that CO2 decreases the difference in nucleation kinetics between PLA under atmosphere and CO2, and increases the secondary nucleation constant. CO2 affects crystallization morphology by activating molecular chain mobility and preventing branching of the original central spherulite, leading to the formation of more perfect crystals.