POLY(VINYL ALCOHOL) GEL SUBLAYERS FOR REVERSE-OSMOSIS MEMBRANES .3. INSOLUBILIZATION BY CROSS-LINKING WITH POTASSIUM PEROXYDISULFATE

Both flat-sheet and tubular composite reverse osmosis (RO) membranes w ere prepared by depositing aqueous solutions of poly(vinyl alcohol) [P VA] and potassium peroxydisulphate [K2S2O8] on asymmetric poly(aryleth er sulphone) [PES] substrate membranes. Heat treatment of the PVA coat ings resulted in crosslinking through carbon-carbon bond formation. Th e crosslinked PVA gels were highly hydrophilic and maintained their in tegrity in acidic and alkaline environments. The effect of PVA concent ration, molecular mass and degree of hydrolysis, K2S2O8 concentration, curing temperature and curing time on RO properties was studied. A si mple manipulation of one or more variables resulted in membranes with widely differing RO properties. Long-term exposure of membranes to a C aSO4 slurry feed indicated a remarkable resistance to abrasion. RO tes ts on a real industrial effluent have underscored the stability and ch emical resistance of these PVA membranes. The insolubilized PVA coatin gs were intended to serve as hydrophilic gel sub-layers on which salt- retention barriers could be formed by interfacial polycondensation. Fo r this purpose, high permeate fluxes are required. The latter can be o btained by adjusting coating solution compositions and fabrication con ditions. These PES-PVA gel-layer composite membranes could also functi on as medium-retention, high-flux RO membranes, even in the absence of an interfacially formed salt-retention barrier.