Epoxy-based solvent-tolerant nanofiltration membranes prepared via non-solvent induced phase inversion as novel class of stable membranes

A novel synthesis method of partially crosslinking a polymer solution prior to casting, has been successfully developed for the preparation of solvent-tolerant nanofiltration (STNF) membranes. STNF merges solvent resistant nanofiltration (SRNF) with aqueous nanofiltration. The feed solution consists of a mixture of solvent(s) and water, requiring a membrane with both high water permeability and solvent stability. In this work, epoxy resins are proposed to meet these requirements. The well-known epoxy curing bulk chemistry via ring-opening reactions has been applied followed by a phase inversion process, to form membranes with intermediate polarity, excellent stability and permeability, making them particularly suitable for the treatment of solvent/water mixtures. Several epoxy monomers were screened, based on size and number of epoxide functional groups. Different amines with varying length and reactivity were chosen as curing agent. Both reagents were dissolved in dimethyl sulfoxide (DMSO) and left to react. The increasing solution viscosity was monitored as a function of time and related to the reaction rate of the epoxy-amine curing system. Integrally skinned asymmetric membranes were prepared via non-solvent induced phase inversion. Filtration experiments were carried out in 20/80 dimethyl formamide (DMF)/water mixtures with Rose Bengal (RB, 1018 g mol−1), Rhodamine 6G (R6G, 479 g mol−1) and Methyl Orange (MO, 327 g mol−1) as solutes. A blend of 2 epoxides, i.e. EPON 1009F (20 wt%) and EPON SU-8 (10 wt%), in DMSO resulted in RB retention of 99+ % and a R6G retention of 77% in DMF/water with a permeance of 0.75 Lm−2h−1bar−1. Addition of tetrahydrofuran (THF) as co-solvent (5/1, DMSO/THF) increased the selectivity further towards a 99% RB and R6G retention and an 85% MO retention with a permeance of 0.29 Lm−2h−1bar−1. ATR-FTIR spectra indicated that the membranes are stable after immersion of 5 days in very harsh conditions, i.e. pH = 0–14, and in a variety of solvents.