Abstract

Introduction of crosslinking into a polyamide structure results in significant improvement in the permeation performance of the corresponding thin film composite (TFC) membranes. In order to identify the source of this improvement, a series of measurements were conducted to ascertain the mechanical, structural, and chemical properties of two polyamides — polymetaphenylene trimesamide (a network polyamide), and polymetaphenylene isophthalamide (a linear polyamide). Permeation measurements revealed that the network polyamide evidences higher water flux as well as salt rejection compared to the linear polyamide. The higher water flux was attributed mainly to the higher hydrophilicity (arising from the hydrolysis of unreacted carboxylic acid groups in the structure) of the network polyamide. Hydrophilicity was found to overwhelm other factors such as the film thickness and chain mobility. On the other hand, the high rejection was found to be due to a combination of high hydrophilicity, greater negative charge, and greater rupture strength of the network polyamide.