Effect of poly(vinyl alcohol) coating process conditions on the properties and performance of polyamide reverse osmosis membranes

Poly(vinyl alcohol) (PVA) is commonly used as a coating material for reverse osmosis membranes to improve their surface properties. However, there are no systematic reports available with respect to the processes conditions and the exact chemistries used for the production of these PVA coatings. In the present study, PVA coatings were fabricated on the outer surfaces of composite polyamide reverse osmosis membranes. The coatings were prepared in both hydrogel film and ultra-thin adsorbed film forms. The processing conditions for the formation of the coatings, such as the PVA concentration, the crosslinking parameters, and the relative humidity (RH) of the curing environment, were studied. The resultant membrane properties, including surface morphology, relative hydrophilicity, tightness, and surface charge, were investigated. The best results were obtained with PVA coating cured at high RH (H-3 and H-4) with membranes exhibiting improved NaCl rejection compared to the virgin membrane, with only a slight decrease in the water flux. The PVA coated membrane (H-4) also exhibited good antifouling performance comparable to the commercial membrane SW30 HR LE. The results suggest that coatings which exhibit a combination of high hydrophilicity and weak tightness result in composite membranes with both high salt rejection and high flux. (C) 2015 Elsevier B.V. All rights reserved.