Preparation of high-flux ultrafiltration membranes by blending strongly charged polymer

Three kinds of high-flux ultrafiltration membranes were fabricated by blending strongly charged polymer [sulfonated poly (phenylene oxide) (SPPO)] with neutral polymer [cellulose acetate (CA), polyethersulfone (PES), or polyvinylidene fluoride (PVDF)]. After blending with SPPO, the pure water flux of CA-SPPO, PES-SPPO, and PVDF-SPPO membrane increase by 3, 76, and 30 times at a transmembrane pressure of 100 kPa. Compared with the unblended membranes, the pore radius of CA-SPPO, PES-SPPO,and PVDF-SPPO membrane increased from 31.9 to 33.2 nm, 26.1 to 28.6 nm, and 19.8 to 25.7 nm, respectively. The addition of strongly charged polymer decreased the thermodynamic stability of casting solutions, promoting the phase inversion process and resulting in highly porous structure. The charged groups and hydrophilicity of the polymer facilitate the formation of an additive concentration gradient (more additive in the active layer), endowing the blend membrane with better hydrophilicity and greater wettability gradient. The high porosity, good hydrophilicity, and larger wettability gradient enable the high permeation of blend membranes.This work shows how the strongly charged polymer affects the formation and performance of blend membrane, which will be useful for designing high-performance membrane.