Effect of mixed crosslinking agents on performance of thin-film-composite membranes

Reverse osmosis (RO) membranes were produced with 5- isocyanate-isophthaloyl chloride (ICIC)/isophthaloyl chloride (IPC) and m-phenylenediamine(MPD) by an interfacial polymerization technique on polysulphone supporting film. The membranes produced were characterized using permeation experiments with salt water and Neo-pentanediol aqueous solution, infrared spectrum, as well as imaging using scanning electronic microscopy. This study showed that the active layer of thin-film-composite membrane (TFC) membranes is polyamide. There is similar morphology for all membrane samples; the surface of the TFC membrane is a dense, finely dispersed grainy structure. With the mass ratio of IPC/ICIC increasing, the flux increased slowly for both NaCl and Neo-pentanediol solutions, but the rejection decreased slowly for NaCl and quickly for Neo-pentanediol. Furthermore, with the feed concentration increasing, there was no obviously different trend of flux for both the NaCl and Neo-pentanediol solutions, but the rejection rate for NaCl increased and that for Neo-pentanediol decreased. These results could be caused by the different chemical structures of the membrane skin layer and the interaction between the TFC membrane skin layer and the Neopentanediol because the linear part in a polymer chain of skin layer increases with the increase of IPC/ICIC mass ratio from the IR result.