Analysis of a Nanocomposite Reverse Osmosis Membrane: Resistance to Chlorine

Chemical degradation of aromatic polyamides (PA) used in reverse osmosis (RO) membranes, attacked by chlorination in the process stream, is of great commercial concern for advances in water treatment efficiency. These advances will be enabled by better analytical methods designed to directly detect oxidant attack for a thin crosslinked membrane (~100 to 200 nm) grafted to a polysulfone support and in which nanofillers may have been incorporated. In this report a thermal gravimetric analysis (TGA) method is suggested to enable this detection. TGA studies focused on temperature of onset of degradation, char yield, activation energy and pre-exponential factor for a typical PA used in RO. The char yield and activation energy values gave the most sensitive identification of chemical changes from aqueous exposure to hypochlorite ion. The method was demonstrated using bulk PA as well as a nanocomposite formed from PA polymerized in the presence of sodium montmorillonite. TGA successfully identified chemical change, particularly through analysis of char yield, for both crosslinked bulk and nanocomposite materials. This technique will be a powerful tool to evaluate the degradation caused by disinfection processes while exploring new formulation approaches to resolve this problem.