Polar polymer membranes via thermally induced phase separation using a universal crystallizable diluent

Dimethyl sulfone (DMSO2) was used as a universal crystallizable diluent to prepare polar polymer membranes via thermally induced phase separation (TIPS). The polar polymers adopted herein include poly(vinylidene fluoride) (PVDF), polyacrylonitrile (PAN) and cellulose acetate (CA). Intensive investigation was carried out to study the phase separation behaviors and the membrane performances. Equilibrium phase diagrams and polarized optical microscope results indicate a solid−solid phase separation mechanism for all the three polar polymer/diluent systems. Scanning electron microscopy observations show that tubular-like pores are irregularly distributed in the PVDF and PAN membranes, whereas a compacted structure can be found in the CA membranes. The pore size, surface porosity, water flux and overall porosity become large when the membranes are prepared with low polymer concentration or at small cooling rate. Results of tensile tests confirm that the mechanical strength of the membranes can be enhanced by increasing the polymer concentration or cooling rate. Moreover, DMSO2 has been efficiently recovered by recrystallization and sublimation. In conclusion, this work may provide a green preparation method to produce polar polymeric membranes via TIPS.