Eco-friendly method for preparation of cross-linked PVA/PAA thin films and membranes thereof for water treatment

Making use of water-soluble polymers as films, membranes, and coatings for aqueous applications has increased over the years, owing to their environmentally benign nature and biodegradability. Interaction of solvent (i.e., water) with highly polar polymers, i.e., water-soluble polymers, results in weakening of cohesive forces between the polymer molecules and increase in the solvent–polymer interaction forces due to the formation of strong hydrogen bonds and polar–polar interactions. This, in turn, leads to the formation of highly swollen polymer gels. The present work focuses on the preparation of water-insoluble ionic thin films using water-soluble blends of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA), by adopting an environment friendly approach. For this purpose, solutions containing varied PVA and PAA contents were prepared in water, and the resulting clear solutions were cast to make films. The cross-linking of cast films were carried out at different temperatures and cross-linking durations. With increasing the cross-linking temperature, properties of the thin films, such as percentage swelling, molecular weight between cross-links, and mesh size, decreased, while cross-link density, gel content, thermal stability and Tg increased. The thin film obtained using solution containing 50% (by wt) of PAA and 50% (by wt) of PVA, and cross-linked at 140 °C, showed optimum swelling properties. Further, cation exchange membranes and thin film composite membranes were fabricated using ion exchange resin and polysulfone substrate membrane, respectively. The composite membrane cross-linked at 140 °C exhibited 95.1% rejection of Na2SO4. Finally, PVA–PAA/polysulfone composite nanofiltration membranes demonstrated Na2SO4/NaCl selectivity in the range of 2.14 to 2.6.Graphical abstract