Positively charged nanofiltration membrane based on cross-linked polyvinyl chloride copolymer

A polyvinyl chloride (PVC)-based positively-charged nanofiltration membrane was fabricated from polyvinyl chloride-graft-poly(N,N-dimethylaminoethyl methacrylate) by heating and crosslinking treatment. We characterized the surface chemical compositions, membranes structures, surface hydrophilicity and surface charges of the prepared membrane. The estimated membrane pore diameter is 1.98 nm and the pore diameters are in the range of 0.5–2.0 nm. The membrane exhibits excellent water permeability (9.3 L m⁻² h⁻¹ bar⁻¹) and salt rejection (93.1% with MgCl₂ solution). Both the heating treatment and crosslinking reaction can diminish the pore size of the precursor membrane. The membrane hydrophilicity is improved after quaternization, leading to higher water permeability compared with the membrane treated by heating only. Moreover, surface quaternization and crosslinking offer the membrane excellent pressure resistance and long-term stability. The prepared nanofiltration membrane has great promise in many applications including water softening and multivalent ion removal.