Surface Modification Of Polyvinylidene Fluoride (PVDF) Membrane By Using The Zwitterionic Substance

Poly （vinylidene fluoride）（PVDF） is a kind of membrane material with excellentperformance, it has been widely used in many areas, it has strong chemical stability,heat resistance, radiation resistance and anti-pollution. Due to its low surface energy,strong hydrophobicity, vulnerable to pollution, the development of PVDF membranehas been limited. In this article, a zwitterionic polymer, poly （3-（methacryloylamino）propyl-dimethyl-（3-sulfopropyl） ammonium hydroxide）（poly （MPDSAH）） was usedas grafting monomer. In order to enhance the hydrophilicity of the membrane andimprove the antifouling properties, MPDSAH was grafted onto the PVDF membraneby three different methods for surface modification. As a representative organicpollutant, Bovine Serum Albumin （BSA） was used to characterize the anti-foulingperformance of PVDF membrane before and after modification. Attenuated totalreflectance-Fourier transform infrared （ATR-FTIR） spectroscopy, X-ray photoelectronspectroscopy （XPS）, the scanning electron microscope （SEM） and contact anglemeasuring were employed to analysis the property and the morphology of the structurebefore and after the membrane surface-modification.First, the modification of PVDF membrane was completed by ultravioletirradiation. Using BenzoPhenone （BP） as Photosensitize, free radicals were producedon the surface of PVDF membrane, after irradiated by Ultraviolet light, and then thehydroxyl were formed in the air. Ceric ammonium nitrate （CAN） as the initiator,N,N’-methylene bisacrylamide as a cross-linking agent, the grafting monomer, MPDSAH was grafted onto the membrane surface in the protection of nitrogen, withthe reaction temperature40°C. The results showed that, the contact angle of the filmdecreased from77.2°to59°, with the illumination time was30min and theconcentration of grafting monomer was2%. That is, the hydrophilicity of themembrane was best, and the pure water flux can stabilize easily, but the removal ratioof BSA didn’t change significantly.Then, in the protection of nitrogen, MPDSAH reacts with PVDF membranedirectly by solution free radical polymerization, with also CAN as initiator and thereaction temperature40°C. It turned out that, when the concentration of graftingmonomer was2%, the contact angle was the smallest, and quickly to0within20s, sothe hydrophilicity of the membrane was best at the moment, and the flux recovery ratiowas the highest. The more of the cycle times of filtration was, the more obvious of theeffect. It can be seen that, the antifouling performance of membrane was improvedafter modification.Finally, the modification of PVDF membrane was completed through two steps.Firstly, poly （2-hydroxyethyl methacry-late）（poly （HEMA）） was grafted to the surfaceof the poly （vinylidene fluoride）（PVDF） membrane by using atom transfer radicalpolymerization （ATRP） method. After that, ceric ammonium nitrate （CAN） as theinitiator, N,N’-methylene bisacrylamide as a cross-linking agent, a zwitterionicpolymer, poly （3-（methacryloylamino） propyl-dimethyl-（3-sulfopropyl） ammoniumhydroxide）（poly （MPDSAH）） was successfully grafted onto the membrane surface byradical polymerization reaction. With the grafting amount （GA） increasing, the amountof adsorption on the film surface was significantly reduced in the high-concentrationBSA solution. The water contact angle （CA） decrease from77.2°to41.7°, within5s to0, and a flux recovery ratio up to94.961%, when the GA reaches288.340μg·cm^-2. Itcan be seen that, the surface hydrophilicity of membrane was significantly enhancedafter modification, and the anti-pollution performance was obviously improved.