Research On PVDF Ultrafiltration Membrane Modified By Amphiphilic Nano-TiO₂Composite Particles

As excellent performance, polyvinylidene fluoride （PVDF） hasbecome a major microfiltration and ultrafiltration membrane materials.But the application of PVDF membrane in the water treatment waslimited because PVDF membrane is hydrophobic and easily compacted.According to the principle of molecular design, the amphiphilicnano-TiO₂composite particles was designed and synthesized, which hasimproved the hydrophilicity and compactibility of PVDF ultrafiltrationmembrane, using them to modify PVDF ultrafiltration membrane, toprepare PVDF ultrafiltration membrane of high water flux, resistant topollution and good compaction.According to the principle of molecular design, the amphiphilicacrylic acid copolymer-silane coupling agent KH570-nano-TiO₂composite particles is designed and synthesized, the synthesis process ofthe composite particles are as follows: the amount of KH570is10wt.%,coupling agent graft ratio is the highest, reached7.62%, the dispersion ofnano-TiO₂significantly improved; when the initiator dosage is0.2%,monomer content is10g, the polymerization temperature is75℃,polymerization time is3h, polymer graft ratio is the highest, reached61.3%.PVDF film-forming process will affect membrane structure andperformance, through experiment results, when PVDF concentration is16wt.%, additive is4wt.%PVP, solvent is DMAc, bath concentration is10%ethanol, temperature is20℃, the performance of the membrane isbetter. Adding amphiphilic nano-TiO₂composite particles, water flue hasincreased from80.8L/（m²h） of pure membrane to223.3L/（m²h） ofmodified membrane, water contact angle has declined from85.6°to47.1°,compaction coefficients has increased from-0.50to-0.04, the water flue,hydrophilic, compaction of the membrane have significantly improved.The method of immersion precipitation phase inversion is used toprepare PVDF membrane. When the composition of the system changesfrom above the critical point of the composition into the metastable phaseregion, the system will occur poor nucleation liquid-liquid phase, otherwise, it will occur rich nucleation liquid-liquid phase. This paper hasproposed a theoretical model in the process of amphiphilic nano-TiO₂composite particles modify PVDF ultrafiltration membrane,hydrophobically modified nano-TiO₂particles stability dispersed in thePVDF membrane body, an "island" structure is formed to enhance themembrane compaction; while during the gel process, the hydrophilicchain of the amphiphilic nano-TiO₂composite particles has isolated andenriched to the surface of the membrane, which can improve thehydrophilic of the membrane. This theoretical model not only explainsamphiphilic nano-TiO₂composite nanoparticles can improve bothhydrophilicity and compaction of PVDF ultrafiltration membrane andalso provides a theoretical guidance and practical significance to develophigh performance PVDF ultrafiltration membrane.