Sulfobetaine-grafted poly(vinylidene fluoride) ultrafiltration membranes exhibit excellent antifouling property

The zwitterionic sulfobetaine methacrylate (SBMA) was grafted on the surface of poly(vinylidene fluoride) (PVDF) membrane via ozone surface activation and surface-initiated atom transfer radical polymerization (ATRP). The steady adsorption of bovine serum albumin (BSA) and γ-globulin were investigated to test the antifouling character after SBMA grafting. Hardly any albumin adsorption was observed, as the grafting density exceeded 0.4 mg/cm2 of polySBMA. The adsorption of γ-globulin was also greatly reduced. To investigate whether the method, ozone surface activation along with ATRP, was able to graft SBMA inside the pores of the membrane, cyclic filtration tests were performed and the ultrafiltration (UF) membrane of wider pore size was used. The cyclic filtration test for BSA yielded an extremely low irreversible membrane fouling ratio (Rir) of 13% in the first cycle, and apparently no irreversible fouling was observed in the second cycle. A more stringent test was carried out by passing the γ-globulin solution. It was found that the virgin PVDF membrane was continuously fouled by γ-globulin after three cyclic operations, while the polySBMA-modified membrane had the Rir value as low as 4.7% in the third cycle. The results indicated that the surface modification via ozone surface activation and ATRP could actually penetrate into the pores of a UF membrane. The polySBMA-grafted PVDF membrane was observed to effectively resist the plasma protein adsorption, and exhibited an extremely low biofouling characteristic during filtration.