Polyamide-imide hollow fiber membranes crosslinked with amine-appended inorganic networks for application in solvent-resistant nanofiltration under low operating pressure

The development of polyamide-imide (PAI) hollow fiber membranes for solvent-resistant nanofiltration (SRNF) in polar aprotic solvents such as dimethylformamide (DMF) under low operating pressure of 2 bar is reported in current study. Highly porous PAI substrates were fabricated and crosslinked with (3-aminopropyl)trimethoxysilane (APTMS). The resultant membranes were solvent-stable and showed higher hydrophilicity and better mechanical property. A 30-min conditioning with either isopropanol or deionized water after the crosslinking reaction was found to affect the morphology of the membranes and thus their nanofiltration performance. Membranes conditioned with isopropanol consistently showed higher solvent fluxes coupled with lower rejections of Rose Bengal (RB) ranging 75-87%. On the other hand, membranes conditioned with deionized water had lower fluxes and high RB rejections of 96-99%. The best-performing membrane achieved a permeability of 6.4 L/(m²hbar) in IPA and 0.9 L/(m²hbar) in DMF with RB rejections of over 97% and 98%, respectively, under 2 bar operating pressure, showing their potential to be used in SRNF processes effectively.