Effect of carbon dioxide on lamellar arrangement in poly(lactic acid) ring band spherulites

In this research, the formation of ring band spherulite of poly(lactic acid) (PLA) under carbon dioxide (CO2) was in-situ studied and the internal lamellar arrangement of ring band spherulite formed under CO2 was revealed for the first time. The spherulites by PLA crystallized under air and different CO2 pressures have been studied, and the surface and internal lamellar arrangement of the ring band spherulites have also been analyzed in detail. It was found that PLA would form ring band spherulite under air and 6 MPa CO2, while the internal structures of the two types of ring band spherulites were different. The surface height difference of ring band spherulites formed under air was small, at 278.9 nm, and the twisting angle of the lamellae was also small. However, the difference in the surface height of the ring band spherulite formed under 6 MPa CO2 was big, reaching 778.3 nm. Through analysis on the internal lamellar arrangement of the ring band spherulite, it was found that the valley for the ring band spherulites formed under 6 MPa CO2 was composed of flat-on lamellae, the ridge was composed of edge-on lamellae and the sudden twist occurred between the flat-on lamellae and edge-on lamellae. image