Hydrophobic Perfluoropolyether-Coated Thin-Film Composite Membranes for Organic Solvent Nanofiltration

Fluoropolymer, with its high chemical stability and hydrophobicity, has great potential in applications involving organic solvents, e.g., organic solvent nanofiltration (OSN). An UV-curable fluorinated polymer, perfluoropolyether (PFPE, Fluorolink AD1700), was coated and polymerized onto a cross-linked polyimide substrate to modify its surface properties for OSN. The PFPE coating can convert the hydrophilic substrate to a hydrophobic membrane and narrow the pore size of the membrane to make it suitable for OSN applications. Different coating concentrations, ranging from 1 to 10 wt %, were applied, and the composite membranes were characterized in various organic solvents (acetonitrile, ethanol, isopropanol, and hexane). The permeances of these solvents were found to be inversely proportional to the products of their viscosities and molar volumes. The separation performance of the composite membrane coated by 10 wt % PFPE exhibited rejections of >90% to orange II sodium salt (MW = 350.32 g.mol(-1)) and remazol brilliant blue (MW = 626.54 g.mol(-1)) in isopropanol. The 7-day tests were also conducted to (1) separate tetracycline from ethanol/tetracycline solutions and (2) recover hexane from hexane/beta-carotene solutions. The fluxes and rejections of both membranes do not fluctuate significantly during the 7-day continuous tests, with a performance comparable with and superior to most literature data. Therefore, the PFPE-coated membranes may have great potential to be next generation OSN membranes for industrial applications.