Influence of rupture strength of interfacially polymerized thin-film structure on the performance of polyamide composite membranes

The permeation properties of a thin-film composite (TFC) membrane depend upon the material properties as well as the structural properties of the polymer forming the active layer. Membranes with the active layers prepared with 1,3,5-benzentricarbonyl chloride (TMC) and aliphatic diamines including dimethylenediamine (DMDA), 1,6-hexamethylenediamine (HMDA), and 1,9-nonamethylenediamine (NMDA) exhibit inferior performance compared to membranes with active layers composed of aromatic diamines including 1,3-benzendiamine (MPDA) and 1,4-benzendiamine (PPDA). It is also observed that the water flux for these membranes decreases as the length of the methylene chain increases due to decreasing hydrophilicity. Furthermore, because of the low rupture strength of the thin-films that form the active layer, the salt rejection also decreases with increasing methylene chain length. The membranes prepared with MPDA and various acyl chlorides including 1,6-hexamethylenedicarbonyl chloride (SC), 1,3-benzenedicarbonyl chloride (IPC), and 1,4-benzene dicarbonyl chloride (TPC) have low rupture strength and poor performance characteristics except for the membrane having network structure, TMC. It is observed that while hydrophilicity has a small effect on the permeation performance of the thin-films its effect of the rupture strength is large. Membranes with weak rupture strength evidence low salt rejection. Hence, the permeation performance of composite membranes with thin-films having weak mechanical strength at high operating pressures depends upon not only the physicochemical properties of the active material including the chemical properties, but also the mechanical strength of the polymer comprising the thin-film.