Using the dimethyl sulfoxide green solvent for the making of antifouling PEGylated membranes by the vapor-induced phase separation process

Abstract

The toxicity of common solvents used in membrane fabrication threatens the environmental sustainability and questions the claim that membrane technology is a green separation technology. Therefore, there is a need for re-orienting membrane fabrication processes towards greener solutions, making use of less toxic, and possibly environmentally friendly solvents. We employed dimethyl sulfoxide (DMSO), a non-toxic solvent, to prepare casting solutions containing polyvinylidene fluoride and an antifouling random copolymer made of polystyrene and poly(ethylene glycol) methyl ether methacrylate (PS-r-PEGMA). Membranes were formed by vapor-induced phase separation (VIPS). They were shown to be homogeneous in terms of structure and surface chemistry (tested by mapping FT-IR), suggesting compatibility of the polymer/copolymer/solvent system and justifying the choice of DMSO. Membrane hydration was drastically improved after adding PS-r-PEGMA with a water contact angle falling from 140° to 47°. As a result, biofouling by Escherichia coli and whole blood was reduced by > 90% in static conditions. During several filtration cycles of a highly fouling Escherichia coli solution flux recovery ratio could be increased from 16% (pristine membrane) to 29% (PEGylated membrane). All in all, this study reveals that low-biofouling homogeneous porous membranes can be prepared by in-situ modification and the VIPS process using a greener approach than traditionally reported.