Study On Modified Silica Nanoparticle－Anionic Waterborne Polyurethane Composite

Modified SiO2 nanoparticles were synthesized by condensation of OH group of silica and the coupling agent. The process of modification reaction and the variation of surface properties were studied in detail. The results of density, solid content, particle size , FT-IR spectroscopy and TEM showed that the coverage of silica surface by coupling agent increased with increasing mol ratio of 3-(trimethoxy-silyl)propyl methacrylate(MEMO)/ SiO2. As the mol ratio reached some value, the surface structure of MEMO anchoring onto the surface of silica could be changed to multilayer. Lipophilic and amphibious monodispersed silica nanoparticles were obtained by controlling the degree of modification. Anionic waterborne polyurethane was prepared with different particle sizes and content of COOH. In this thesis, the prepolymer process and phase-reversion process was investigated particularly. The dispersions with different average particle size were obtained by controlling the content of COOH and the ratio of NCO/OH. Regarding as a diblock copolymer, WPU had definite CMC value and could be Self-emulsified in water.Finally, the structure transform of modified silica nanoparticle-WPU composite dispersion was investigated and characterized. The phase-reversion method was compared with in situ hydrolysis method. By the phase-reversion method, 'Strawberry' aggregations were formed and there were strong hydrogen bond associations between amide of polyurethane segment and silanol of silica, resulting in dissociation of hydrogen bond of carboxyl groups in polyurethane. The hydrophobic segments in the core of polyurethane could not dissociate in water and encapsulate lipophilic silica particles spontaneously, while the lipophilic liquid of TEOS could be emulsified into the hydrophobic core of polyurethane.