Effect Of Surface Modification Of Nano-tio₂ On The Corrosion Resistance Of Polyurethane

Nano-TiO2 has a large specific surface area and micro-size, showing the unique physical and chemical properties. In recent years, the use of the characteristics of nano-TiO2 preparation of functional coatings has become a research hotspot. The surface of nano-TiO2 was graft modified in this paper, and to study the nano-TiO2 addition on corrosion resistance of polyurethane varnish and polyurethane top-coating. Finally, we explored the surface modification of nano-TiO2 via the RAFT polymerization to resolve the high content of nano-TiO2 coating the dispersion problem.Suface modification of nano-TiO2The surface of nano-TiO2 was modified by coupling agent KH-570. FT-IR and TG results showed that the KH-570 was grafted onto the surface of nano-TiO2 successfully, grafting rate was 21.42%. Sedimentation experiments showed that modified nano-TiO2 had better dispersion in the polyurethane paint diluent than the unmodified nano-TiO2.In addition, nano-TiO2 was modified by PMMA-b-PS via reversible addition–fragmentation chain transfer (RAFT) polymerization. FT-IR, TG, XPS and 1H NMR results showed that RAFT agent was immobilized on the surface of TiO2, and RAFT polymerization was successful. The content of PMMA-b-PS grafted onto the TiO2 surface was approximate 80.5%.The effect of rutile nano-TiO2 on the corrosion resistance of polyurethane varnishThe modified and unmodified rutile TiO2 was added into polyurethane varnish to prepare nano-TiO2/polyurethane composite coatings.Viscosity test results showed that the coatings with modified nano-TiO2 were thixotropy, and the addition of modified TiO2 was good to the storage and construction of paint. Field emission electron microscopy results showed that modified nano-TiO2 was dispersed in polyurethane coatings most evenly as the content was 3%, and particle size was about 60 nm.Nano-TiO2/polyurethane composite coatings were immersed in saline(wt%=5) for 56 d and electrochemical impedance tests for 2880 h. The experimental results showed that the addition of modified nano-TiO2 can significantly improve corrosion resistance of coatings. When the content of modified nano-TiO2 was 3%, the corrosion resistance was the best, After 56 d saline immersion, the physical properties of composite coating decreased. Compaered with varnish, the pencil hardness of composite coatings with 3% modified nano-TiO2 improved 3 levels, the gloss retention rate increased by 14%, and the anti impact properties was 6 times than that of varnish. The adhesion rank decreased from 1 to 3, while the adhesion of varnish d ecreased from 0 to 4. In the electrochemical impedance test, the resistance of composite coatings was approximately 1011Ω.cm2. After immersed 2880 h, the resistance of coating with modified TiO2 was significantly higher than that of varnish and coating with unmodified nano-TiO2. When the content of modified nano-TiO2 was 3%, the coating resistance was 2.6×108Ω.cm2 and was 160 times of the varnish, and showed a time constant characteristics in the immersion process.The effect of mixed nano-TiO2 on the corrosion resistance of polyurethane top-coatingThe mixture of rutile and anatase nano-TiO2 was modified by KH-570 and added into the polyurethane top-coating to prepare nano-TiO2/polyurethane composite coating.Field emission electron microscopy results showed that nano-TiO2 dispersed evenly in polyurethane as the content was 4%, and the dispersion was worse with the increase of TiO2 content.Composite coatings were immersed in saline ( wt%=5 ) for 56 d and electrochemical impedance tests for 1680 h. The results showed that: the coatings with 4% mixture modified nano-TiO2 had relatively better corrosion resistance. After 56 d saline immersion, compaered with original formulation, the pencil hardness of composite coatings with 4% modified nano-TiO2 improved 3 levels, the flexibility increased by 10 mm, and the adhesion rank improved 2 levels. In the electrochemical impedance test, the coating resistance of had a small difference at the beginning of immersion. After immersed 1680 h, the resistance of coating with 4% modified TiO2 was the biggest and was 100 times as high as the varnish, indicating that the coating can protect the metal matrix.