Poly(vinyl alcohol) gel sub-layers for reverse osmosis membranes. III. Insolubilization by crosslinking with potassium peroxydisulphate

Abstract

Both flat-sheet and tubular composite reverse osmosis (RO) membranes were prepared by depositing aqueous solutions of poly(vinyl alcohol) [PVA] and potassium peroxydisulphate [K 2S 2O 8] on asymmetric poly(arylether sulphone) [PES] substrate membranes. Heat treatment of the PVA coatings resulted in crosslinking through carbon-carbon bond formation. The crosslinked PVA gels were highly hydrophilic and maintained their integrity in acidic and alkaline environments. The effect of PVA concentration, molecular mass and degree of hydrolysis, K 2S 2O 8 concentration, curing temperature and curing time on RO properties was studied. A simple manipulation of one or more variables resulted in membranes with widely differing RO properties. Long-term exposure of membranes to a CaSO 4 slurry feed indicated a remarkable resistance to abrasion. RO tests on a real industrial effluent have underscored the stability and chemical resistance of these PVA membranes. The insolubilized PVA coatings were intended to serve as hydrophilic gel sub-layers on which salt-retention barriers could be formed by interfacial polycondensation. For this purpose, high permeate fluxes are required. The latter can be obtained by adjusting coating solution compositions and fabrication conditions. These PES-PVA gel-layer composite membranes could also function as medium-retention, high-flux RO membranes, even in the abasence of an interfacially formed salt-retention barrier.