PVA-PSSS membranes for alkali recovery through diffusion dialysis: effect of alkoxysilanes

Poly(sodium-p-styrene-sulfonate) (PSSS) is synthesized by the method of ARGET ATRP, then mixed with polyvinyl alcohol (PVA), and cross-linked with different alkoxysilanes, that is, tetraethoxysilane (TEOS), 3-aminopropyltriethoxysilane (APTS), or gamma-glycidoxypropyltrimethoxysilane (GPTS). The obtained flexible cation-exchange membranes have water uptakes (W-R) of 46.8-120.7% and ion-exchange capacities (IEC) of 1.03-1.64 mmol/g. The category of the alkoxysilanes strongly influences the membrane properties. The membrane from GPTS has the highest thermal stability with T-d (temperature at 5% weight loss) of 267.4 degrees C, the highest IEC, and the lowest swelling degree in 65 degrees C water, which is due to the dual cross-linking of Si-O-Si and C-O-C between GPTS and PVA. When applied for diffusion dialysis (DD) process of NaOH/Na2WO4 mixture, the membranes exhibit excellent alkali flux. The OH- dialysis coefficients (U-OH) are in the range of 0.0072-0.0208 m/h, higher than PVA blank membrane (0.0077 m/h) or commercial poly(2,6-dimethyl-1,4-phenylene oxide)-based membrane (0.004 m/h) (Tianwei Membrane Co., Ltd., Shandong of China). The separation factors (S) are in the range of 16.8-25.7, higher than PVA-PSSS membrane cross-linked with formaldehyde (S = 8.0). Hence, the membranes can be potentially applied in DD process for alkali recovery.