Effect Of Organic Base On The Properties Of PVDF Membrane And Its Functionalization

Poly(vinylidene fluoride)(PVDF) was one of the most widely used fluorinatedpolymer membrane material because of its good physical-chemical stability andexcellent processability to prepare membrane. However, high hydrophobicity made iteasy to produce proteins adsorption and precipitation in the membrane surface. Itsseparation flow decreased rapidly and limited its application in the water treatment.Therefore, the hydrophilic modification of PVDF membrane was an effective methodto improve its resistance to contamination and its separation performance. Meanwhile,the single performance PVDF membrane could not meet the needs of its applicationsin various fields with more and more widespread use. Various functional PVDFmembranes came into being and the functionalization of PVDF membrane became ahot topic at present. In this study, an organic base polyethylene polyamine wasdirectly added to the PVDF casting solution. In the homogeneous solution, organicbase reacted with PVDF. Dehydrogenation fluoride reaction on PVDF generatedactivated C=C with the strong alkaline of organic base. It could improve thehydrophilicity of the film, and provide favorable condition for the furtherfunctionalization. Functional monomers such as acrylic acid (AAc) anddimethylamino ethyl methacrylate (DMAEMA) were grafted onto PVDF membranesurface through UV grafting process and pH-sensitive and antibacterial membraneswere prepared. Dehydrogenation fluoride reaction happened on PVDF withpolyethylene polyamine in the homogeneous solution. Oxidation reaction wasaccompanied with dehydrogenation fluorine reaction and introduced other groupsincluding C-O, C-N and C=O. With the increase of ethylene polyamine content, thecontact angle of the film decreased. The hydrophilic of membrane growed, but theporosity, roughness and other factors of the membrane surface did not change. Thefinger-shaped holes in the cross section and pore size on the surface of membrane alsobecame larger and larger, while the PVDF membrane structure did not changed. Thefiltration performance of membrane was controlled by the hydrophilicity and pore size together. With the content of polyethylene polyamine increasing, thehydrophilicity of membrane enhanced and the water flux of membrane rised. Thepores size of membrane also increased. The BSA retention rate decreased. When thecontent of polyethylene polyamine was less than6%, the pure water flux ofmembrane and the BSA retention rate increased slowly So the hydrophilicity ofmembrane played a dominant role. When the content of polyethylene polyamine wasmore than6%, the pure water flux of membrane increased rapidly and the BSAretention rate decreased significantly. The pores size of membrane was the dominantfactor.Acrylic acid (AAc) was grafted onto PVDF membrane surface through UVirradiation process. The results indicated that the acrylic acid was grafted on thesurface of PVDF membrane with a chemical bond. A series of pH sensitivemembranes with different grafted-ratio of acrylic acid were prepared. Thegrafted-ratio of acrylic acid was changed with acrylic acid concentration and thereaction time. When the time was reached20min, the grafting was the best. When thetime was more than20min, the grafted-ratio of acrylic acid substantially unchanged.The grafted-ratio was increased with increasing concentration of acrylic acid. But, thegrafted-ratio was significantly reduced when the concentration exceeded40%. Inorder to obtain a high grafted-ratio PVDF membrane, the concentration and reactiontime must be controlled well. The grafted membrane had acrylic acid chain that wasshrinked or expanded with the pH value. The effective aperture and pure water flux ofmembrane were also changed. The pure water flux was most changed prominentwhen the pH value between3to5because the pKa of acrylic acid was about4.7.Different grafted-ratio of membrane had different pH-sensitive. The pH-sensitive wasprominent when grafted-ratio was18.7%.Antibacterial monomer dimethylamino ethyl methacrylate (DMAEMA) wasgrafted onto PVDF membrane surface by using UV irradiating process. Thequaternary on the membrane surface was quaternized by using of quaternaryammonium benzyl chloride. Antimicrobial PVDF membrane was prepared. Thedifferent degree of quaternization of PVDF membranes were contacted with the bacteria with E. coli. The antibacterial effect was verified with different times.Antibacterial experiment showed that the antibacterial effect of quaternizedmembrane was significantly better than the original film. The antibacterial effect wasincreased with increasing degree of quaternization and the contact time. Meanwhile,the antibacterial effect of PVDF membrane had not changed much after acid picklingby dilute hydrochloric. It indicated that acid had no influence on the antibacterialeffect of antibacterial PVDF membrane.