A chemical imidization method to avoid pore collapsing and selective layer thickening of PMDA-ODA polyimide nanofiltration membranes

To suppress pore collapsing and selective layer thickening of Poly (pyromellitic dianhydride-co-4,4'-oxydianiline) (PMDA-ODA) nanofiltration (NF) membrane during imidization, we proposed a novel two step method.Specifically, a PMDA-ODA polyamic acid (PAA) polymer dope was cast on top of a non-woven polyester fabric and then underwent non-solvent induced phase inversion to form a PMDA-ODA PAA membrane.The membrane was subsequently dried by solvent exchange and chemically imidized to form PMDA-ODA PI membrane.Compared with the thermally imidized PMDA-ODA PI membrane, which had a thick selective layer of 14.5 μm and pure water permeability of 1.5 L/(m 2 •h•bar), membrane fabricated using the new method had a thinner selective layer of 1.04 μm and 7 times higher pure water permeability of 10.4 L/(m 2 •h•bar) without losing rejections.Other than that, the NF membrane also showed good separation properties in organic solvent systems.It showed rejections of 87%~95% to Rose Bengal in DMF, THF, and DMSO, with stable permeabilities of 6.1-8.0L/(m 2 •h•bar), at a trans-membrane pressure of 20 bar for at least 24 h.Therefore, the PMDA-ODA PI membranes had great potential for NF in both water and organic solvent systems.