Interfacially polymerized thin film composite membranes on microporous polypropylene supports for solvent-resistant nanofiltration

Interfacial polymerization (IP) is a powerful technique for fabrication of thin film composite (TFC) membranes. The polymers used most often as support are polysulfone (PS) or polyethersulfone (PES). These supports have limited stability in organic solvents. In this work, microporous polypropylene (PP) flat film and hollow fiber membranes were used as a support to fabricate TFC membranes for nanofiltration by the IP technique. Porous polypropylene membranes can provide substantial chemical, pH, and solvent resistance and are therefore suitable as supports for fabricating TFC membranes functioning as solvent-stable nanofiltration membranes. The surface and the pore interior of polypropylene flat sheet and hollow fiber membranes were hydrophilized first by pre-wetting with acetone followed by oxidation with chromic acid solution. A standard procedure to successfully coat the hydrophilized flat film and hollow fiber membranes was developed next. The monomeric system chosen for IP was poly(ethyleneimine) and isophthaloyl dichloride. The TFC hollow fiber membranes were characterized by nanofiltration of safranin O (MW 351) and brilliant blue R (MW 826) dyes in methanol. Rejection values of 88% and 43% were achieved for brilliant blue R and safranin O, respectively at a transmembrane pressure of 413 kPa in the TFC hollow fiber membranes. Pressure dependences of the solvent flux and solute rejection of the TFC membranes were studied using the modified flat sheet membranes up to a pressure of 965–1241 kPa. Solvent flux increased linearly with an increase in the transmembrane pressure. Solute rejection also increased with an increase in the transmembrane pressure. All modified membranes were also characterized using scanning electron microscopy. Extended-term solvent stability of the fabricated membranes was studied in toluene; the membranes demonstrated substantial solvent stability in toluene.