PVA-based hybrid membranes from cation exchange multisilicon copolymer for alkali recovery

Abstract

Cation exchange multisilicon copolymers i.e. copolymers containing pendent siloxane and SO3Na groups are developed from the copolymerization of sodium styrene sulfonate (SSS) and γ-methacryloxypropyl trimethoxy silane (γ-MPS). The copolymerization process can proceed smoothly without formation of gel. The copolymers are compatible with water, and can produce transparent and homogeneous solutions when mixed with poly(vinyl alcohol) (PVA), so that transparent and compact hybrid membranes are obtained.The membranes are thermally and mechanically stable, with initial decomposition temperatures of 237–273°C, tensile strength of 9.1–26.0MPa and elongation at break of 12.4–21.1%. The membranes have a water uptake (WR) of 30.0–54.8% and swelling degrees of 46–115% in 65°C water, which are mainly controlled by the content of Si(OCH3)3 groups in the mutlisilicon copolymers. Diffusion dialysis (DD) separation of NaOH/Na2WO4 solution indicates that the alkali dialysis coefficients (UOH) are in the range of 0.010–0.011m/h, higher than the values of commercial membrane (0.00137m/h) and other polymer based hybrid membranes (0.0014–0.0022m/h). The membrane structure and properties are correlated with the ions transport mechanism, revealing interesting findings as to the influence of IEC and different functional groups on DD behavior.