Development of polyamide/polyacrylonitrile thin film composite RO membranes by interfacial polymerization assisted with an aromatic/aliphatic organic solvent mixture

Abstract

The proper control of polymerization is a prerequisite in fabrication of thin film composite reverse osmosis (RO) membranes. But it not trivial when hydrophilic substrates are used. Herein, we report an innovative approach which involves using an aromatic/aliphatic solvent mixture of toluene and n‐hexane as the organic phase for interfacial polymerization. Membranes were tuned by using a customized developed polyacrylonitrile (PAN) substrate and exploring the impacts of organic solvent and curing temperatures on their morphology and performance characteristics. Results revealed that increasing the temperature of organic phase to 20°C improved salt rejection significantly to 98.6% with the flux of 16.1 LMH. However, its further increase to 30°C was not beneficial due to formation of a looser chain packing which led to rejection drop. In addition, raising curing temperature to 90°C was not favorable due to transformation of surface morphology from ridge‐and‐valley to nodular structure, accompanied with defective sites at the selective layer and insufficient degree of crosslinking evidenced by declines in both flux and rejection to 11.1 LMH and 83.4%, respectively. Overall, the findings suggested that an optimal performance could be obtained by using a solvent mixture of toluene/n‐hexane (1,1) and setting organic solvent and curing temperatures to 20 and 70°C, respectively.