POLY(VINYL ALCOHOL) GEL SUBLAYERS FOR REVERSE-OSMOSIS MEMBRANES .1. INSOLUBILIZATION BY ACID-CATALYZED DEHYDRATION

Both flat-sheet and tubular composite reverse osmosis (RO) membranes w ere prepared by depositing aqueous solutions of poly (vinyl alcohol) ( PVA) and a dehydration catalyst on asymmetric poly (arylether sulfone) (PES) substrate membranes. The PVA coatings were insolubilized by hea t treatment to create stable hydrophilic gel-layer membranes. The infl uence of variables such as PVA concentration, catalyst concentration, curing time, and curing temperature was investigated. It was shown tha t a simple manipulation of one or two variables could lead to membrane s with widely differing salt retention and water permeability characte ristics. The insolubilized PVA coatings were intended to serve as hydr ophilic gel sublayers on which ultrathin salt-retention barriers could ultimately be formed by interfacial polycondensation. For this purpos e, high-flux gel layers were required, whereas salt-retention capabili ties were not regarded as important. However, the promising salt reten tions obtained at 2 MPa (up to 85% NaCl retention and 92% MgSO4 retent ion) showed that some of these PES-PVA composite membranes could funct ion as medium-retention, medium-flux RO membranes, even in the absence of an interfacially formed salt-retention barrier. (C) 1993 John Wile y & Sons, Inc.