Oil–water emulsion separation using ultrafiltration membranes based on novel blends of poly(vinylidene fluoride) and amphiphilic tri-block copolymer containing carboxylic acid functional group

Abstract

Amphiphilic tri-block copolymer (TBC) consisting of a central polystyrene block and two lateral polyacrylate-carboxylic acid blocks was successfully prepared by reversible addition fragmentation chain transfer (RAFT) process using telechelic polystyrene as a macro-RAFT agent. Ultrafiltration membranes based on the blends of poly(vinylidene fluoride) (PVDF) and TBC were fabricated in the weight ratios of 95/5, 90/10 and 85/15 by solution casting and phase inversion process. The fabricated membranes were characterized by scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry. Water contact angle measurement, permeate flux of bovine serum albumin solution, and filtration experiments including pure water permeation test, molecular weight cut-off test and oil–water emulsion filtration test were used to evaluate the wettability and anti-fouling properties of the membranes. The blend membranes exhibited higher flux and molecular weight cut off values when compared to the neat PVDF membrane. The high water permeability of the blend membranes may be attributed to the presence of porous skin layer with hydrophilic surface due to the presence of TBC. The flux recovery ratio (FRR) values for the permeation of BSA protein solution showed that the blend membranes (FRR=67–78%) possessed superior fouling resistance property than that of the neat PVDF membrane (FRR=57%). The blend membranes showed about 2.5 times higher water flux with ~99% oil rejection at 2bar operating pressure for the engine oil–water emulsion feed when compared to that of the neat PVDF membrane. A linear regression analysis of various fouling models involving both pore blocking and cake formation was performed for the membranes in the separation of oil–water emulsion.