The Study On Preparation Of Amphiphilic Nano-tio₂ Composite Particles And Their Application In Pvdf Ultrafiltration Membranes

Polyvinylidene fluoride (PVDF) used for developing ultrafiltration membrane is an optimal material with good withstand voltage characteristics and combination property. On the base of study of modified PVDF ultrafiltration membrane at home and abroad, the hybrid PVDF ultrafiltration membrane with the property of high flux, resist compression, fouling resistant was prepared through introducing the modifier of amphipathic nano-TiO₂ complex, which can improve the property of the hydrophilicity and compactibility of PVDF ultrafiltration membrane, synthesized according to the principle of molecular design. Meanwhile, the mechanism of film-forming and modifying was discussed.According to the principle of molecular design, the amphipathic nano-TiO₂ complex was designed, with the nano-TiO₂ as its core, silane coupling agent KH-570 as its hydrophobic chain, and AA and MMA copolymer as its hydrophilic segment. The optimal parameters of the complex were as follows: KH-570 3wt. % (Relative to the weight of nano-TiO₂); AA and MMA 60wt.%( The ratio of monomer AA and MMA was kept between 40% and 50%); initiator 0.08wt. %; monomer and initiator added drop by drop; reaction temperature 80℃. Under these conditions, the grafting rate of monomer could reach 80% and the complex showed good hydrophilic properties. The molding process was studied. it was discovered that the hydrophilicity, compatibility and anti-fouling of the complex membrane was significantly improved and membrane flux could achieve 90mL.cm^-2.h^-1 when PVDF was 20wt.%, PVP 3wt.%, amphipathic nano-TiO₂ particles 4wt.%, pure water used as coagulation solution and gelation temperature 20²5℃.The modifying mechanism of amphiphilic nano-TiO₂ complex was studied and a modifying physical model was presented. The modified nanoparticles, because of the hydrophobic chain in the surface, can stably disperse in the surface and the inside of PVDF membrane. An "island" structure was formed by particles decentralizing in the membrane to enhance the membrane compaction; while those particles dispersing in the surface of membrane can increase the thick degree of the membrane surface and intensify the hydrophilic properties of membrane. Surface segregation and enrichment of the polymer chains grafted in the surface of the particle occurred during the gel process, which can significantly improve the hydrophilicity, antifouling and flux of the membrane.