Positively-charged nanofiltration membrane formed by quaternization and cross-linking of blend PVC/P(DMA-co-MMA) precursors

To explore low-pressure-driven nanofiltration (LPDNF) membranes with high permeate flux, a novel preparation route was proposed and investigated. First, an amphiphilic copolymer of poly (methyl methacrylate-co-dimethylaminoethyl methacrylate) (P(MMA-co-DMA)) was synthesized via free-radical copolymerization, and then blended with polyvinyl chloride (PVC) to fabricate precursor membranes via non-solvent induced phase separation (NIPS) process. Utilizing the quaternization and cross-linking reaction between p-xylylene dichloride (XDC) and tertiary amine units in PVC/PMMA-co-DMA precursor membranes, positively charged PVC/PMMA-co-DMA LPDNF membranes were obtained. Element alanalysis, X-ray photoelectron spectroscopy and scanning electron microscopy were employed to characterize the composition and morphology of the membranes. Effects of PMMA-co-DMA content and XDC concentration on the LPDNF membranes' performance were studied and discussed. With the optimized condition, the NF membrane showed the highest salt rejection (R) and water flux (J), e.g., RMgCl2=89.1%, JMgCl2=22.1 L/(m2 h) and RNaCl=45.1%, JNaCl=27.6 L/(m2 h) at a pressure of 0.3 MPa. Besides, the rejections of the LPDNF membranes for inorganic salts increased in an order of Na2SO4