Preparation and characterization of chlorine resistant thin film composite polyamide membranes via the adsorption of various hydrophilic polymers onto membrane surfaces

The surfaces of the reverse osmosis (RO) membranes prepared by an interfacial polymerization method on the polysulfone supports in our lab were modified by the adsorption of the three hydrophilic polymers, poly(vinyl sulfonic acid) (PVSA), poly(ethylenimine) (PEI) and poly(vinyl alcohol) (PVA). Using the ‘salting-out effect’, these polymers, representative of anionic, cationic and neutral polymers, respectively, were used to investigate which adsorbed polymer is the most resistant to chlorine attack. The surface properties of the adsorbed RO membranes were characterized to confirm the adsorption by using contact angle measurement and scanning electron microscopy (SEM). The performance of chlorine-resistance RO membranes was measured through their evolution, before and after hypochlorite exposures in 3,450 ppm NaOCl solution for desired time points. This was determined in terms of pure water permeability and salt rejection. In order to determine the most dominant factor contributing to chlorine resistance, experiments were carried out under several conditions. The candidate factors included coating time, concentration of coating solution, ionic strength, and salt types. In general, as the coating time and concentration increased, the chlorine resistance increased for any salt used. Among the three materials, PVSA showed the greatest chlorine resistance of ca. 62,000 ppm·h, under the determined conditions, ionic strength (IS)=0.2 Mg and coating time of 60 s. The order of chlorine stabilities for the coating materials was determined to be PVSA, PEI, and PVA. It was found that the chlorine resistance of any polymer-coated membrane is superior to the pristine RO membrane. [graphic not available: see fulltext]