Abstract
Based on a two-step polymerization method, two sulfobetaine-based zwitterionic monomers, including 3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide (MPDSAH) and 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA), were successfully grafted from poly(vinylidene fluoride) (PVDF) hollow fiber membrane surfaces in the presence of N,N′-methylene bisacrylamide (MBAA) as a cross-linking agent. The mechanical properties of the PVDF membrane were improved by the zwitterionic surface layers. The surface hydrophilicity of PVDF membranes was significantly enhanced and the polyMPDSAH-g-PVDF membrane showed a higher hydrophilicity due to the higher grafting amount. Compared to the polyMEDSA-g-PVDF membrane, the polyMPDSAH-g-PVDF membrane showed excellent significantly better anti-protein-fouling performance with a flux recovery ratio (RFR) higher than 90% during the cyclic filtration of a bovine serum albumin (BSA) solution. The polyMPDSAH-g-PVDF membrane showed an obvious electrolyte-responsive behavior and its protein-fouling-resistance performance was improved further during the filtration of the protein solution with 100 mmol/L of NaCl. After cleaned with a membrane cleaning solution for 16 days, the grafted MPDSAH layer on the PVDF membrane could be maintain without any chang; however, the polyMEDSA-g-PVDF membrane lost the grafted MEDSA layer after this treatment. Therefore, the amide group of sulfobetaine, which contributed significantly to the higher hydrophilicity and stability, was shown to be imperative in modifying the PVDF membrane for a stable anti-protein-fouling performance via the two-step polymerization method.
Highlights
Due to its extraordinary mechanical property, high chemical resistance, and good thermal stability, polyvinylidene fluoride (PVDF) has been recognized as one of the most attractive polymers in the membrane industry and widely used in many separation applications [1,2]
The typical spectra of the polyMPDSAH-g-PVDF and polyMEDSA-g-PVDF membranes are displayed in Figures 1 and 2
The results indicate that the hydrophilicity of the polyMPDSAH-g-PVDF membrane was superior to that of the polyMEDSA-g-PVDF membrane
Summary
Due to its extraordinary mechanical property, high chemical resistance, and good thermal stability, polyvinylidene fluoride (PVDF) has been recognized as one of the most attractive polymers in the membrane industry and widely used in many separation applications [1,2]. Many researchers have confirmed that sulfobetaine coatings on various polymer membranes effectively resist protein adsorption and subsequently significantly retard bacterial biofilm formation [3,14,15,16,17,18,19]. 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA), could be successfully grafted onto the PVDF hollow fiber membrane surface via alkaline treatment and atom transfer radical polymerization (ATRP) [20]. Poly(2-hydroxyethyl methacryl ate) (poly(HEMA)) chains were first grafted onto the outer surface of the PVDF membrane via atom transfer radical polymerization (ATRP) to provide the initiation sites for subsequent cerium (Ce (IV))-induced graft copolymerization of sulfobetaine monomers (MPDSAH or MEDSA) in the presence of N,N′-methylene bisacrylamide (MBAA) as a cross-linking agent. The hydrophilicity, protein-fouling-resistance, electrolyte-responsiveness, and stability of polyMPDSAH-g-PVDF and polyMEDSA-g-PVDF membranes were compared under similar conditions. The stability of the modified PVDF membranes was evaluated by examining the surface composition and anti-protein-fouling performance after membrane cleaning
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