Design And Anti-biofouling Performance Of Ultrafiltration Membrane Modified By Quaternary Ammonium Compounds

Polyvinylidene fluoride(PVDF)is a high-performance polymer material that has high mechanical strength,as well as excellent stability against acids and alkalin.These properties make it an ideal material for the production of ultrafiltration membranes,which is widely used in the water treatment industry.The PVDF ultrafiltration membrane is inherently hydrophobic,making it prone to contact with various pollutants then cause serious biological pollution during the separation process.This can negatively impact separation efficiency and shortening service life of the membrane.Therefore,developing a type of ultrafiltration membrane that possesses both hydrophilicity and antibacterial properties is crucial in alleviating biological pollution on the membrane surface and ensuring long-term,stable operation of the membrane process.This study specifically focused PVDF powder and designed star shaped block polymers based on atom transfer radical polymerization(ATRP)technology.Then these polymers were used to create di-functional membranes with antibacterial and hydrophilic properties through the phaseinversion method.And the ultrafiltration performances of these membranes were evaluated,including their ability to prevent biological pollution during usage.The main research content and conclusions are as follows.1.A series of quaternary ammonium compounds(DMAEMA-Cn)were synthesized,which displayed antibacterial activity and contained carbon chains of different lengths.These compounds were then grafted from PVDF molecular chains through ATRP to create graft polymers(PVDF-g-Cn)with antibacterial properties.To characterize the chemical structure of graft polymers,we utilized infrared spectroscopy(ATR-FTIR),nuclear magnetic resonance spectroscopy(1H NMR),and X-ray photoelectron spectroscopy(XPS).The results indicated that quaternary ammonium compounds with different carbon chain lengths were effectively prepared and then grafted from PVDF molecular chains.The next step was utilizing these graft polymers to produce co-blended membranes,designated as PVDF-g-Cn-M,through the soaking phase-inversion method.The performance changes of various modified membranes were tested in sequence.The results showed that the PVDF-g-C12-M membrane,which had a lightly dense layer and a loosely porous internal structure,exhibited an higher antibacterial rate of 83.3%and 69.1%against E.coli and E.faecalis,respectively.This suggests that the introduction of quaternary ammonium compound polymer brushes on the membrane surface played a significant role in enhancing the antimicrobial property of the PVDF membrane.2.Sulfobetaine methacrylate(SBMA)is a common choice for modifying membrane surfaces to improve their hydrophilic properties and resistance to protein pollutants.This amphoteric ion is highly biocompatible and hydrophilic,making it an effective solution for enhancing the antifouling ability of membranes.Based on the above research,a variety of random polymer brushes were synthesized by incorporating SBMA into the one-step ATRP reaction and adjusting the molar ratio of the two functional monomers,DMAEMA-Cn and SBMA.Additionally,the antifouling performance of the membrane surface was further enhanced through hydrophilic modification.The surface elements of the membrane were analyzed to determine the chemical composition and property enhancement.The SBMA polymer brushes,which possess strong hydration ability,and the DMAEMA-Cn polymer brushes,which exhibit antibacterial ability,were both found to migrate successfully to the surface of the membrane.As the SBMA molar ratio increased,the pore size of the membrane surface decreased,resulting in a smoother and more hydrophilic surface.By balancing both"prevention" and "attack" strategies,we were able to create a type of ultrafiltration membrane with exceptional performance,possessing dual functions of hydrophilicity and antibacterial property.The PVDF-g-50%SBMA-M membrane exhibited an antibacterial rate of 54.3%and 51.0%against E.coli and E.faecalis,respectively.And it means this membrane effectively prevented the attachment of more bacteria and killed the attached bacteria.Additionally,the chemically bonded functional groups were expected to be stronger.The results of dynamic filtration experiments indicated an improved ability to resist biofouling.