IMPROVING HYDROPHILICITY AND PROTEIN ANTIFOULING OF ELECTROSPUN POLY(VINYLIDENEFLUORIDE-HEXAFLUOROPROPYLENE) NANOFIBER MEMBRANES

Poly（vinylidenefluoride-hexafluoropropylene） （PVDF-HFP） nanofiber membranes with improved hydrophilicity and protein fouling resistance via surface graft copolymerization of hydrophilic monomers were prepared. The surface modification involves atmospheric pressure glow discharge plasma （APGDP） pretreatment followed by graft copolymerization of poly（ethylene glycol） methyl ether methacrylate （PEGMA）. The success of the graft modification with PEGMA on the PVDF-HFP fibrous membrane is ascertained by X-ray photoelectron spectroscopy （XPS） and attenuated total reflectance Fourier transform infrared measurements （ATR-FTIR）. The hydrophilic property of the nanofiber membranes is assessed by water contact angle measurements. The results show that the PEGMA grafted PVDF-HFP nanofiber membrane has a water contact angle of 0° compared with the pristine value of 132°. The protein adsorption was effectively reduced after PEGMA grafting on the PVDF-HFP nanofiber membrane surface. The PEGMA polymer grafting density on the PVDF-HFP membrane surface is measured by the gravimetric method, and the filtration performance is characterized by the measurement of water flux. The results indicate that the water flux of the grafted PVDF-HFP fibrous membrane increases significantly with the increase of the PEGMA grafting density.

Effect of protein on PVDF ultrafiltration membrane fouling behavior under different pH conditions： interface adhesion force and XDLVO theory analysis

To further detem3ine the fouling behavior of bovine serum albumin （BSA） on different hydrophilic PVDF ultrafiltration （UF） membranes over a range of pH values, self-made atomic force microscopy （AFM） colloidal probes were used to detect the adhesion forces of membrane-BSA and BSA BSA, respectively. Results showed that the membrane-BSA adhesion interaction was stronger than the BSA-BSA adhesion interaction, and the adhesion force between BSA-BSA-fouled PVDF/PVA membranes was similar to that between BSA-BSA-fouled PVDF/PVP membranes, which indicated that the fouling was mainly caused by the adhesion interaction between membrane and BSA. At the same pH condition, the PVDF/PVA membrane-BSA adhesion force was smaller than that of PVDF/ PVP membrane-BSA, which illustrated that the more hydrophilic the membrane was, the better antifouling ability it had. The extended Derjaguin-Landau-Verwey Overbeek （XDLVO） theory predicts that the polar or Lewis acid-base （AB） interaction played a dominant role in the interracial free energy ofmcmbrane-BSA and BSA BSA that can be affected by pH. For the same membrane, the pH values of a BSA solution can have a significant impact on the process of membrane fouling by changing the AB component of free energy.

Grafting Branch Length and Density Dependent Performance of Zwitterionic Polymer Decorated Polypropylene Membrane

Branch length and density have critical effects on membrane performances; however, it is regarded to be traditionally difficult to investigate the relationship due to the uncontrolled membrane modification methods. In this study, zwitterionic polymer with controlled grafting branch chain length（degree of polymerization） and grafting density（grafting chains per membrane area） was tethered to the microporous polypropylene membrane surface based on the combination of reversible addition-fragmentation chain transfer（RAFT） polymerization technique with click reaction. The modified membranes were tested by filtrating protein dispersion to highlight the correlations of branch chain length and grafting density with the membrane permeation performances. The pure water flux, the flux recovery ratio are positively and significantly, and the irreversible fouling negatively and significantly correlated with grafting density. These results demonstrate that the larger the coverage of the membrane with poly{[2-（methacryloyloxy）ethyl]-dimethyl-（3-sulfopropyl） ammonium hydroxide}（PMEDSAH）, the higher the pure water flux and the higher the flux recover ratio, and the lower the irreversible fouling, which shows that high grafting density is favorable to fouling reducing.