The crystallization morphology and process of stereocomplex crystallites of polylactide under CO2: the effect of H-bonding and chain diffusion

Abstract

CO₂ could affect the crystallization behavior of polylactide (PLA) homo-crystallites (HC) due to its influence on the chain mobility, while the effect of CO₂ on the crystallization of stereocomplex crystallites (SC) is still unknown. In this manuscript, the crystallization process of SC under CO₂ was in situ observed by high-pressure POM, and the crystal morphology was further studied by AFM and CLSM. During growth, the nucleation and the branching of lamellae for SC was limited by CO₂ at higher temperatures due to the plasticization effect, and fewer crystals with tangential lamellae were shown. The crystal morphology exhibited pressure dependence. At lower pressure, many “grooves” were shown on the SC crystal surface and the crystals became more perfect with increasing pressure, while the depth of “grooves” decreased gradually and the crystals became imperfect under higher pressure. Compared with SC, the HC showed deeper “grooves” and perfect crystals with increasing pressure monotonously. It was inferred that the weakened H-bonding and the increasing diffusion of molecular chains at high temperature and pressure caused the different SC and HC crystallization mechanisms under CO₂.