Preparation And Characterization Of Antimicrobial And Antipollution PES Ultrafiltration Membrane

This study is based on the fouling problem of ultrafiltration membrane used inthe desalination pretreatment process. The aim is to prepare a novel ultrafiltrationmembrane modified with capsaicin to improve its capability of antimicrobial pollution.In this study, polyether sulfone (PES) membranes were prepared via phase inversionmethod. The technological conditions of PES membrane preparation were optimizedby studing the composition of casting solution and membrane forming conditions.Firstly,The effects of different solvents（DMAC, DMF，NMP）and additives（LiCl,PEG400，TW80）on the membrane structure and performance were discussed. Then,taking the pure water flux as the indexes, orthogonal experimental design was adaptedto determine the influence degree of the following actors on membrane performance:PES concentration, additive concentration and gelation temperature and composition.Based on the optimized technological conditions, the ultrafiltration membraneswere prepared using PES (18%), compound additives and DMAC as materials, andwere modified by adding a capsaicin derivative monomer named MBHBA which hasexcellent antibacterial properties. The thermal decomposition process of PESmembrane before and after modification was tested by TGA（Thermal GravimetricAnalysis）and the introduction of MBHBA monomer was examined.The visualinformation of the surface as well as cross-sectional morphology of the membraneswas characterized using SEM (scanning electron microscopy).The hydrophilicproperties of membranes were stufied by contact angle testing. And separationperformance of membranes was characterized by pure water flux and rejection rate of1.0g/L bovine serum albumin (BSA) solution determination. Finally, theantibacterial property of modified membrane was evaluated by colony countingmethod with E. coli being used as the indicator bacterium. The experimental resultsshowed that the hydrophily of modified PES membrane slightly increased due to theexistence of MBHBA monomer. The pure water flux increased from120.6L/(m2·h)to 139.2L/(m2·h)with the content of MBHBA1%, and it increased significantly asMBHBA content rising, while the rejection rate decreased gradually. When thecontent of MBHBA is6%, the rejection rate of BSA dropped to65.8%.Antibacterialexperimental results showed that the PES ultrafiltration membrane modified withMBHBA can restrict more than70%E. coli.With the purpose of further enhancing the antipollution capacity of the PESmembrane, monomers with good hydrophily (acrylic acid and acrylamide) werecopolymerized with MBHBA to synthetize capsaicin copolymer which was then usedto prepare PES membrane via blend modification.So the modified ultrafiltrationmembranes possess excellent antibacterial properties as well as good hydrophilicity toimprove its anti-foulingability. AIBN was used as initiator to cause the unsaturateddouble bonds in MBHBA monomer to generate free radicals, so that to synthetizecapsaicin copolymer with acrylic acid or acrylamide by copolymerization.Theexistence of the hydrophilic groups and MBHBA characteristic functional groups inthe capsaicin copolymer was tested by IR spectra. The research results of fungusresistance of capsaicin copolymer indicated that the antibacterial ratio to E. coli wasinsignificant at low concentration (<5mg/mL). As the concentration of capsaicincopolymer increases, the antibacterial ratio rises.When its concentration is30mg/mL,capsaicin copolymer can strongly inhibited the growth of E. coli.PⅡand PⅣ, which had better antibacterial property of the synthetic capsaicincopolymers, were selected to prepare modified PES ultrafiltration membrane. Thenthe modified membrane’s microscopic morphology and structure, hydrophilicity,separation performance and antibacterial ratio to E. coli were characterized by SEM,contact angle, water flux and BSA rejection rate, and colony countingmethodrespectively.The results suggested that the hydrophily of blend PES ultrafiltration membranemodified with capsaicin copolymers had greatly improved: When capsaicincopolymer content was3%, the contact angle of membrane surface reduced from74°of the unmodified membrane to below60°. However, the water flux greatly reducedcompared with unmodified membrane at the same time because of the dense pore structure of membrane. The modified membranes got remarkable hydrophilicproperties, water flux and higher antibacterial ratioto E. coli when the content ofcapsaicin copolymers was approximately at the level of1%or more.