POLY(VINYL ALCOHOL) GEL SUBLAYERS FOR REVERSE-OSMOSIS MEMBRANES .2. INSOLUBILIZATION BY CROSS-LINKING WITH POLY(METHYL VINYL ETHER-ALT-MALEIC ANHYDRIDE)

Composite reverse osmosis (RO) membranes were prepared by depositing a queous compatible blends of poly(vinyl alcohol) [PVA] and poly(methyl vinyl ether-alt-maleic anhydride) [MVE-alt-MAH] on flat-sheet asymmetr ic poly(arylether sulphone) [PES] substrate membranes. Insolubilizatio n of the polymer blend films was accomplished by the formation of inte rchain ester crosslinks during heat treatment. The crosslinked films w ere intended to serve as hydrophilic gel sub-layers on which ultrathin salt-retention barriers could ultimately be formed by interfacial pol ycondensation. The RO properties (salt retention, permeate flux) of PV A-based membranes prepared in the absence and presence of H2SO4 cataly st 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 p ermeability characteristics varied with the pH of the feed solution. T his was attributed to the different degrees of ionization of the first and second carboxyl groups of the maleic acid residues in hydrolyzed MVE-alt-MAH at different pH values. Different ratios of PVA and MVE-al t-MAH were evaluated. A PVA: MVE-alt-MAH molar ratio of 3.5: 1 resulte d in gel-layer membranes with sufficiently high water permeabilities f or application as gel sub-layers in RO membranes.