Dye/salt fractionation of zwitterion-modified poly(ether sulfone) membranes

Zwitterion modification of polymeric membrane has shown a promising technique in the field of dye/salt fractionation using membrane filtration. In this study a carboxybetaine-based zwitterion was developed by two steps: first the synthesized p (St-r-DMAEMA) copolymer was blended with the poly (ether sulfone) (PES) during membrane preparation. Indeed, N,N '-dimethylaminoethyl methacrylate (DMAEMA) was incorporated as precursor comonomer into styrene (St) to immobilize final zwitterion structure. Then the prepared membranes were treated through quaternary amination with sodium chloroacetate (SCA) as second step. The random copolymers synthetized with different monomer ratios were characterized using NMR, FTIR, DSC, TGA and viscometry. The copolymer containing 30% DMAEMA (St70-r-D30) not only shows sufficient miscibility with PES but also tends to move to the surface during making membrane. The zwitterionic membrane prepared from 21 wt% PES solution containing St70-r-D30 as copolymer additive showed flux recovery ratio as high as 95.3% and irreversible fouling of 4.7% under a simple water flushing. In addition, modified membranes maintained low salt rejection rates (<5%) while showing satisfactory dye rejection (>95%) for the dye/salt mixtures with 20 gL(-1) NaCl which is very promising for textile wastewater treatment.