The Effect of Sulfonated Polysulfone on the Compatibility and Structure of Polyethersulfone-Based Blend Membranes

Polymer blend is the most common method to improve membrane hydrophilicity, in which the compatibility between the polymers is an important factor affecting the structures and properties of blend membranes. Polyethersulfone (PES)-based blend membranes were prepared from PES/polysulfone (PSf)/N, N-dimethylacetamide (DMAc) and PES/sulfonated polysulfone (SPSf)/DMAc casting solutions with water as coagulant via immersion precipitation phase inversion, respectively. The compatibility of blend systems and membrane formation process were investigated through thermodynamics and kinetics analyses. Ultrasonic through-transmission measurements were performed to quantify the rate of membrane formation during the phase inversion process. The effect of SPSf on the compatibility and morphologies of PES-based blend membranes were characterized by scanning electron microscopy (SEM), pure water flux and BSA rejection. Results indicated that the PES/PSf blend system was partially compatible, leading to instantaneous demixing and the obtained membrane with finger-like structure, whereas the PES/SPSf blend system was entirely miscible, resulting in delayed demixing and the obtained membrane with sponge-like asymmetrical gradient structure. Simultaneously, the surface segregation behavior of SPSf with hydrophilic sulfonic acid groups during mutual diffusion process resulted to the enhancement of PES/SPSf membrane hydrophilicity. Consequently, PES/SPSf blend membrane showed excellent water permeability and better antifouling ability.