Fabrication of a novel hollow fiber composite membrane with a double-layer structure for enhanced water treatment

In surface modification of polymer membranes, permeate flux is normally decreased with the enhancement of rejection and antifouling properties. Herein, a new method is proposed to beat the permeability-selectivity trade-off and endow polymer membranes with more functions: a double-layer polypropylene/styrene-maleic anhydride (SMA) copolymer hollow fiber composite membrane was fabricated via interfacial suspension co-polymerization. The pore structure of the hydrophilic SMA layer was optimized by manipulating the polymerization and phase separation in the mixed solvents. The formation mechanism of the pores was systematically investigated. Phase separation, the length of the SMA molecular chain, and its selective swelling in the mixed solvents were the key factors for pore formation. Compared with the pristine membrane, the water flux of the optimized membrane PPM2 was significantly increased from 105.5 to 570.0 L/m(2)h, and rejections were highly elevated from 81.4% to 97.2% for bovine serum albumin (BSA), 49.8% to 96.5% for Congo red, and 17.6% to 68.9% for methylthionine chloride. The antifouling properties were simultaneously strengthened, and the flux recovery ratio was increased from 68.6% to 95.2% for the BSA solution and 71.5% to 92.8% for the oil/water (O/W) emulsion. The separation efficiency of the O/W emulsion was up to 99.9% because of the double-layer structure with asymmetric wettability.