Tailoring the cell morphology and characteristics of poly(lactic acid) foams via a stereocomplex crystallization-assisted phase separation strategy

Stereocomplex (SC) crystallization between poly(L-lactide) (PLLA) and its enantiomer poly(D-lactide) (PDLA) provides an effective approach to enhancing the physicochemical properties of poly(lactic acid) (PLA). In this study, we systematically investigate the effects of SC crystallization on the thermal-induced phase separation (TIPS) behavior of PLA enantiomers/1, 4-dioxane solutions, as well as the microstructure, pore morphology, and properties of the resulting PLA foams. The results show that increasing PDLA content leads to a higher relative fraction of SC crystallites and alters the cell morphology, transitioning from fishbone-like tubular pores to irregular small pores formed by densely packed submicron particles. In-situ Raman and X-ray analyses reveal that this phenomenon is closely related to the TIPS mechanism of PLA enantiomers in 1, 4-dioxane, where SC crystallites induce a shift from solid-liquid phase separation to crystallization-assisted liquid-liquid phase separation. Compared to alpha-crystal PLA foams, SC-type foams exhibit a larger specific surface area and greater thermal resistance. Additionally, the unique pore morphology of SC-type foams results in a more hydrophobic surface, demonstrating effective oil-water separation properties. Overall, this study elucidates the interaction mechanism between SC crystallization and phase separation during the TIPS process and proposes a novel strategy for fabricating PLA porous materials.