As global industry advances toward sustainability and high-performance manufacturing, porous membranes are increasingly required to combine environmental friendliness and precise microstructural control. The integration of thermally induced phase separation (TIPS) and non-solvent-induced phase separation (NIPS) can be termed hybrid phase separation (HPS), which has emerged as a promising technique for creating porous polymers with intricate hierarchical structures. Nevertheless, systematic investigations into the associated crystallization and pore formation remain scarce. In this work, the crystallization behavior and pore formation of poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) porous membranes prepared via HPS were investigated. During processing, the PLLA/PDLA/1,4-dioxane system undergoes TIPS to generate microscale pores, while residual ethanol in the pore walls induces the secondary NIPS, forming nanoscale subpores within the microporous framework. A moderate ethanol content promotes the development of stereocomplex crystals that enhance structural stability, whereas excessive ethanol accelerates phase separation, suppressing crystallization due to a shortened crystal growth time. This study provides insights into the HPS technique and contributes to the design of bio-based porous materials with tunable structural and functional characteristics.
Fan et al. (Mon,) studied this question.