Poly(vinyl alcohol) gel sub-layers for reverse osmosis membranes. II. Insolubilization by crosslinking with poly(methyl vinyl ether- alt-maleic anhydride)

Abstract

Composite reverse osmosis (RO) membranes were prepared by depositing aqueous compatible blends of poly(vinyl alcohol) [PVA] and poly(methyl vinyl ether- alt-maleic anhydride) [MVE- alt-MAH] on flat-sheet asymmetric poly(arylether sulphone) [PES] substrate membranes. Insolubilization of the polymer blend films was accomplished by the formation of interchain ester crosslinks during heat treatment. The crosslinked films were intended to serve as hydrophilic gel sub-layers on which ultrathin salt-retention barriers could ultimately be formed by interfacial polycondensation. The RO properties (salt retention, permeate flux) of PVA-based membranes prepared in the absence and presence of H 2SO 4 catalyst were measured at various pH values of the feed solution (2,000 mg/l NACl). The highest permeate fluxes were obtained when membranes were cured in the presence of acid catalyst. The salt-retention and water permeability characteristics varied with the pH of the feed solution. This was attributed to the different degrees of ionization of the first and second carboxyl groups of the maleic acid residues in hydrolysed MVE- alt-MAH at different pH values. Different ratios of PVA and MVE- alt-MAH were evaluated. A PVA: MVE- alt-MAH molar ratio of 3.5: 1 resulted in gellayer membranes with sufficiently high water permeabilities for application as gel sub-layers in RO membranes.