Surface modification of a polyamide reverse osmosis membrane for chlorine resistance improvement

A surface modified polyamide (PA) thin film composite (TFC) membrane was prepared using in-situ polymerization of sorbitol polyglycidyl ether (SPGE) on the membrane surface immediately after interfacial polymerization of TFC membranes. This modification was conducted to protect the chlorine-sensitive sites of the PA membrane using a chlorine-resistant hydrophilic SPGE polymer. The optimum preparation condition of the modified PA TFC reverse osmosis membranes was investigated, and then the successful modification of the membrane was confirmed using various analytical tools including Fourier transform infrared spectroscopy, a zeta potential analyzer, a contact angle analyzer, X-ray photoelectron microscopy, scanning electron microscopy, and atomic force microscopy. The modification converted the surface of the membrane to a more neutral, hydrophilic, and smooth surface. With increasing SPGE concentration in the coating solution, molecular overlapping of the coating polymer led to a denser coating layer, which resulted in declined flux but increased salt rejection. Chlorination tests showed that the modification of the membrane using SPGE ring-opening polymerization improved chlorine stability.