Improved chlorine resistance of polyamide thin-film composite membranes with a terpolymer coating

Polyamide (PA) thin-film composite (TFC) membranes are easily degraded under the attack of active chlorine in feed water or during chemical washing. In the present work, a random terpolymer of 2-acrylamido-2-methyl propanesulfonic acid, acrylamide and 1-vinylimidazole (P(AMPS-co-Am-co-VI)) was designed as a coating material to improve the chlorine tolerance of PA TFC membrane. The terpolymer was first synthesized via conventional free radical polymerization and then coated onto commercial available PA TFC membrane by dip-coating process. The changes in surface chemistry, morphology, hydrophilicity/hydrophobicity and charge characteristics of the membrane after surface coating were investigated in detail. It was shown that the incorporation of terpolymer coating created a more neutral, hydrophilic, and smooth membrane surface. The chlorine resistance of the membranes was evaluated by comparing the permeation and separation properties of the unmodified and modified membranes after chlorine exposure. And the experimental results indicated that the chlorine tolerance of PA TFC membranes was improved significantly, especially in acid environment. The coating layer prevents the selective layer from the attack of active chlorine as a barrier layer more than a sacrificial layer. The coating material and method developed in this work can facilitate the design and manufacture of highly chlorine resistant TFC membrane for seawater desalination and industrial separation.