Separation performance of poly(vinyl alcohol) based nanofiltration membranes crosslinked by malic acid for salt solutions

Abstract

In this study, poly(vinyl alcohol) (PVA) based nanofiltration (NF) membranes were prepared by coating a thin PVA film on polysulfone ultrafiltration support substrates. The PVA film was cross-linked using malic acid in the presence of HCl as a catalyst. The impacts of crosslinker content and PVA molecular weight on physicochemical properties and separation performance of the prepared membranes were investigated. The obtained membranes were characterized using FTIR spectra, swelling degree, and sessile drop contact angles, respectively.  Then, the separation performance of the NF membrane was systematically evaluated for pure water; magnesium sulfate (MgSO4) as well as sodium chloride (NaCl) solutions using a custom fabricated 4-cell crossflow desalination system. On increasing the malic acid content, the extent of crosslinking degree increased and disrupted the crystallinity of the PVA film. The salt rejection of the prepared membranes was found to increase and then decrease through the maximum point of malic acid content for 20 wt%, while the water permeability showed the opposite trend. Moreover, the results revealed that the prepared membrane with higher molecular weight exhibited lower water permeability but better salt rejection.