PVA-based cation exchange hybrid membranes with multifunctional groups prepared from ternary multisilicon copolymer

Abstract

Multisilicon copolymers are put forward as new types of crosslinking agents for preparing ion exchange hybrid membranes. Ternary multisilicon copolymer is prepared from copolymerization of maleic anhydride (MA), sodium styrene sulfonate (SSS) and γ-methacryloxypropyl trimethoxy silane (γ-MPS). The obtained copolymer is then crosslinked with polyvinyl alcohol (PVA) to yield cation exchange hybrid membranes. The membranes contain multifunctional groups including SO3Na, COOH and SiOH from the multisilicon copolymer and COH from PVA, which can form crosslinking structure through SiOSi, SiOC and (CO)OC bonding.The membranes have the tensile strength (TS) of 25.6–32.1MPa and elongation at break (Eb) of 68–161%. The swelling resistance at room temperature or 65°C increases with the dosage of multisilicon copolymer. The membranes are used in diffusion dialysis (DD) process for potential application in alkali recovery. The dialysis coefficients of OH− (UOH) are in the range of 0.011–0.019m/h at 20°C and 0.021–0.031m/h at 40°C, higher than those of commercial sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) membrane (0.002m/h at 25°C) or other PVA-based hybrid membranes. The DD performances cannot be well explained by the ion transport mechanism based on “three phase” membrane structure, or by the change of water uptake (WR), ion exchange capacity (IEC) and fixed group concentration (CR). The uniqueness of the membrane structure, as well as the presence of multifunctional groups has to be taken into account, which gives some insight as to future DD membrane design objectives.