Preparation And Characterization Of Nano-silica/Fluorinated Polyacrylate Composite Emulsions

With the introduction of nano-silica into fluorinated acrylate system, the product not onlycan own hardness and heat resistance of SiO₂but also can obtain excellent surfaceperformance of fluorinated acrylate such as hydrophobicity, oleophobicity and stain resistance.In addition, the composite can obtain more excellent performance due to synergies betweeninorganic and organic components.In this paper, organic nano-silica was frstly synthesized by sol-gel method withmethylmethacrylate （MMA） and butyl acrylate （BA） in the micelles as dispersing media,tetraethoxysilicate （TEOS） as precursor, KH-570as modifier. Nano-silica/fluorinatedpolyacrylate composite emulsions were prepared by by miniemulsion polymerization andcore-shell polymerization, using modified nano-silica, methyl methacrylate （MMA）, butylacrylate （BA） dodecafluoroheptyl methacrylate（DFMA） and acrylic acid （AA）. The structureand properties of the nano-silica/fluorinated polyacrylate composite emulsions were studied.The main contents and the results of this paper are as following:Firstly, the effects of pH value, hydrolysis time, kind and content of emulsifier, contentof HD, content of KH-570on stability of pre-emulsions, the content of silica and the thegrafting ratio of nano-silica were studied. The result showed that nano-silica pre-emulsionswith high stability and nano-silica with high grafting ratio were obtained, when DNS-86wasused as emulsifier, the content of DNS-86was4%, the pH value was2, the content of HDwas2.5%, the mass ratio of KH-570to nano-silica was2:5, and the hydrolysis time was24h.FT-IR analysis showed that KH-570did participate in copolymerization.Secondly, the nano-silica/fluorinated polyacrylate composite emulsions were directlyprepared by miniemulsion polymerization and core-shell polymerization using the nano-silicapre-emulsions. The influence of ultrasonic conditions, filming temperature, amount ofemulsifier, co-emulsifier, initiator, modified nano-SiO₂and DFMA on the polymerizationprocess and the comprehensive performance of latex films was investigated as well. Thestructure and morphology of the latex particles, the surface properties and heat resistance ofthe latex films was characterized through particle size analysis（DSL）, transmission electronmicroscopy（TEM）, Fourier transform infrared spectroscopy（FT-IR）, contact angle（CA）, and thermogravimetry analysis （TG）. The results showed that nano-silica grafted with doublebond and fluorinated acrylate monomers are involved in the emulsion polymerization. Theresultant particles had core-shell structure obviously, the particle size of the composite latexincreased comparing to polyacrylate emulsion.The optimal system stability and smalldiameter of composite latex particles could be obtained with the ultrasonic time of9min andultrasonic power of120w. When the total amount of emulsifier （DNS-86） was4%, the contentof HD was2.5%, the optimal system stability and water resistance of latex films could beobtained. The water resistance of the latex films increased when the amount of nano-silicaincreased from0to7.5%, and then decreased slightly. So the appropriate amount ofnano-silica was about5.5%. The hydrophobicity of latex films increased with the amount ofDFMA increasing. When the amount of nano-SiO₂was5.5%and the amount of DFMA was6%, the water contact angle of latex films with the deionized water was up to102.9°. Thehydrophobicity and thermal stability of polyacrylate latex films could be greatly improvedwith the introduction of nano-silica and DFMA. The water contact angle of latex filmsreached the maximum with the filming temperature of50℃.