Abstract: Isothermal cold crystallization behavior of polylactide (PLA) at atmosphere was studied by using a differential scanning calorimeter (DSC), and the crystalline morphology of PLA samples obtained at different temperature for 100 min was characterized by using a polarized optical microscopy (POM). Using CO2 as a media, PLA samples isothermally crystallized at 5 MPa at different temperature for 100 min were prepared in a high-pressure vessel. The crystal morphology and crystalline structure of PLA samples prepared at atmosphere and under CO2 were compared by a POM and a wide-angle X-ray diffractometer (WAXD), respectively. The results showed that CO2 had a significant plasticizing effect on PLA and enhanced the mobility of PLA macromolecular chains, resulting in cold crystallization at a lower temperature. Compared with PLA samples crystallized at atmosphere, the size of spherulites decreased, the quantity of spherulites increased and the degree of perfection increased for PLA samples treated under CO2 while the final crystallinity decreased.

Key words: polylactic, carbon dioxide, cold crystallization