Preparation And Characterization Of Nano-silica/Fluorianted Polyacrylate Composite Emulsion And High Hardness, Transparent And Hydrophobic Coatings

Recently, transparent and hydrophobic materials have exhibited huge potential in thefields of building materials, automobile glass, historic monuments protection, telescope lenses,and solar panels and so on. Due to its unique properties of amphiphobicity, thermal stabilityand chemical inertness, low dielectric constant and good biocompatibility, fluorinatedpolymers are mostly used to prepare hydrophobic materials. Accompanying withstrengthening of consciousness of environment protection and energy, and demands ontransparency of hydrophobic materials on some special cases, people pay more and moreattentions to prepare aqueous fluorinated polyacrylate composite latex and transparent andhydrophobic coatings. However, the large-scale applications of fluorinated polyacrylate latexand its transparent and hydrophobic coatings are still limited by the high price of fluorinatedacrylate monomers and weak mechanical property of fluorinated polyacrylate latex film.Nano-silica is a kind of inorganic nanoparticles with excellent properties and wide rawmaterial source，which can improve organic polymers in their hardness，scratch-resistance，UV-resistance and so on. Thus, how to incorporate nano-silca into fluorinated polyacrylatelatex simply and effectively and make nano-silica well dispersed in fluorinated polymers toprepare eventually the high hardness, transparent, hydrophobic and thermal stable coatings isalways the goal of material researcher.In this work，nano-silica/(fluorinated) polyacrylate composite latex were prepared by thecombined techniques of in stiu polymerization, seeded emulsion polymerization andminiemulsion polymerization. The high hardness, transparent and hydrophobic compositelatex coatings were prepared and the properties and structures of composite latex and resultantfilms were investigated in detail. The main research contents and achievements are listed asfollowing:First，the stable dispersion of nano-silica/acrylate monomers (DSAM) was prepared byemulsion method with methylmethacrylate (MMA) and butyl acrylate (BA) in the micelles asdispersing media, tetrethoxysilicate (TEOS) as prescuror and γ-methacryloylpropyltrimethoxysilane (MPS) as modifier. The effects of emulsifier content, mass ratio of oil towater (Ro/w), and silica content on stability of DSAM and the effects of pH value andemulsifier content on yields of silica were studied. The optimal conditions for DSAM arefollows: pH value is2, DNS-86content is6wt%, Ro/wis1:1, silica content is5.5wt%.Fourier transform infrared spectroscopy (FTIR) confirmed that silica formed from TEOS inemulsion system and oleophilic surface of silica were achieved by condensation of hydroxyl groups between silica and hydrolysis from MPS. The methacryloyl groups grafted on thesurface of silica improved the stability of silica dispersed in acrylate monomer droplets andprovided double bond for the subsequent polymerization with acrylate monomer.Second, the monodisperse nano-silica/polyacrylate composite latex was successfullyprepared by the combination of in situ polymerization and semi-continuous seeded emulsionpolymerization based on the stable DSAM. In the above polymerization, the reactiveemulsifier DSN-86, MMA, BA and initiantor KPS were used. The results show that the pencilhardness decreases while adhesion increases with the increase of MMA/BA mass ratio. Thenano-silica can improve the pencil hardness. When the nano-silica content is5.5wt%, thecomposite latex film has the high pencil hardness of3H. The incorporation of nano-silica intocomposite film can also improve thermal stability and performance of shielding fromultraviolet.Third，the stable and monodisperse nano-silica/fluorinated polyacrylate latex and theresultant transparent and hydrophobic composite films with high hardness and thermalstability were prepared by in situ polymerization and semi-continuous emulsionpolymerization. The fluorinated acrylate monomers were introduced into the second stage. Itis found that more fluorinated content, higher water contact angle and MMA/BA mass ratiohas important an influence on water contact angles. When DFHMA content was6wt%andMMA/BA mass ratio was1/3, water contact angle of the compostite film could reach121.0o.In addition, the longer fluorinated side chain will resulted in higher transmittance and lowerhaze. The incorporation of nano-silica can obviously improve the hardness of the compositefilm. Nano-silica can also improve the thermal stability and ultraviolet shielding performanceof the composite film. TEM, FTIR and XPS confirm that there are good combined forcebetween nano-silica and fluorinated polyacrylate at nano-scale and fluorinated groups has agradient distribution along the depth of film. The possible mechanism of migration andenrichment of fluorinated groups to the film surface under different MMA/BA mass ratio wasproposed.Fourth，the stable nano-silica/fluorinated polyacrylate composite latex was prepared byin situ miniemulsion polymerization with MMA, BA and PFOMA as monomers in thepresence of oleophilic nano-silica. Kinetics of miniemulsion polymerization was studied. Themonomer conversion and rate of polymerization was influenced by reaction temperature, thecontent of emulsifier and initiator. The apparent activation energy of reaction of miniemulsionpolymerization was171.9kJ/mol. DLS analysis shows that main nucleation mechanism is monomer droplet nucleation. The measurement of water contact angle shows that theincreasing fluorinated monomer content will improve the hydrophobicity of the compositefilm. Compared with non-fluorinated latex film, the composite film not only has betterhydrophobicity but also has a certain self-healing ability after immersion in water or acid orbase. Moreover，the composite film has good transparency. The increase in SDS content andnano-silica content will decreases the transmittance while the increase in nano-silica willincrease the haze. The transmittance reduces and haze rises after water immersion treatment.The incorporation of nano-silica into composite film also improves the thermal stabilitydramatically. Compared with that of film without nano-silica, T10%of composite film with6.0wt%silica content improved by67.0oC. The construction of nano-micro double roughness onthe surface of paper fibers was achieved when paper fibers was treated by the composite latexand the water contact angle of the paper fibers improved from0oto128.5o, which illustratesthat paper fibers has transformed from total hydrophily to strong hydrophobicity.