Preparation And Properties Of Waterborne Composite Protective Coatings

Waterborne coatings were widely used in the corrosive industry due to their non-flammable danger and low VOC emissions.Compared with solvent-based coatings,waterborne coatings still had poor corrosion resistance.In this paper,silane-modified nano-TiO₂ was mixed with aqueous epoxy dispersion to prepare nano-composite coating on Q235 steel surface,and electrochemical impedance spectroscopy experiment,neutral salt spray experiment,laser confocal,Fourier transform infrared spectroscopy and other means were used.The properties of silane-modified particles and their composite coatings were characterized.The optimum process of silane grafting solution and the corrosion resistance mechanism of silane-modified nano-TiO₂/waterborne epoxy composite coatings were determined.In this paper,the relationship between the conductivity of silane chemical grafting solution and the degree of hydrolysis of 3-aminopropyltriethoxysilane?APTES?was studied.The optimal APTES hydrolysis process was determined to be:10²5%APTES?mass fraction?.Ethanol 15g,hydrolysis temperature 35?,hydrolysis time 10h,grafting time 7h,adding appropriate amount of triethylamine to adjust pH=8,nano titanium dioxide 3g.When the amount of APTES was 20%,the molecular density of nano-TiO₂ grafted APTES was the largest,which was 11.78 APTES/nm²,and the average particle size of the nanoparticles was increased by 10?m compared with that before modification.The silane-modified nano-TiO₂ FT-IR spectroscopy showed that the APTES molecule and the nano-TiO₂ were bonded by chemical bonds.Under the condition of lower silane content grafting,the ratio of the APTES molecule to the nano-TiO2 was higher.The corrosion resistance of silane-modified nano-TiO₂/waterborne epoxy composite coatings was evaluated by neutral salt spray test and electrochemical impedance spectroscopy.The corrosion resistance of composite coatings under different grafting conditions was studied.The optimum process conditions for preparing composite coatings were determined:silane grafting time 7h,silane grafting temperature 35?,APTES content 20%,color The base was 1.5%.The test results showed that the impedance modulus of the low-frequency region after the composite coating immersed in 3.5%NaCl solution for 72h was 1.6×10⁶?·cm²,which was more than 700 times that of pure epoxy coating.After immersed for 168h,the impedance modulus was still up to 3.39×10⁵?·cm²,which was more than 200 times of pure epoxy coating;after 168h neutral salt spray test,the silane-modified nano-TiO₂/waterborne epoxy composite coating had no obvious damage except for artificial scratches.Corrosion,which indicated that the silane-modified nano-TiO₂/waterborne epoxy composite coating had strong corrosion resistance.Combined with silanization of nano-TiO2 by Fourier transform infrared spectroscopy,the APTES molecular nano-TiO2particles grafted with a high proportion of single-tooth helical structure were not firmly bonded to the epoxy matrix,and the composite coating prepared was not suitable for long-term corrosion.The three-dimensional microscopic morphology of the composite coating was observed by laser confocal.Combined with corrosion resistance experiments,it was determined that the silane-modified TiO₂/EP composite coating enhanced the corrosion resistance of the coating from two levels:at the interface of the coating-corrosive medium,the generation of micropores was reduced and the density was increased.Uniform dispersion effect in the organic matrix,with APTES as the connecting bridge,enhanced the bonding strength between the nano-TiO₂ and the epoxy matrix,and prolonged the corrosion path of the corrosive medium in the coating,thereby achieving the corrosion resistance effect.