Preparation Of TiO₂NPs And Its Effect On The Surface Of The External Wall Coating

Exterior wall coating with the characteristics of convenient installation andlow-cost, is strongly advocated to promote by the nation. However, the insufficient ofcontamination resistant ability of exterior coating is a common problem which restrictsthe promotion of exterior coating. In recent years, with the application of TiO₂photocatalytic technology in the self-cleaning technology, photocatalytic technology hasbecome the most attractive method in preparing self-cleaning coating. However, thephotocatalysis may decompose the organic material, accelerate aging, and has adverseimpact on the durability of the coating. In view of this, the nano-TiO₂was made intoslurry and sprayed on coating surface, whose excellent UV shielding effect can reducecoating damage caused by photocatalysis. In this paper, the relationship between paintfilm water sensitivity and coating contamination resistance was studied.In this paper, taking titanium（Ⅳ） n-propoxide as titanium source, hydrophilic TiO₂and hydrophobic Tio2of anatase were prepared by hydrothermal method under the testconditions of180°C for4h，The particle size of hydrophilic-TiO₂was40nm, and ithad the reunion phenomenon, while hydrophobic-TiO₂was only7nm, the grain-sizedistribution was even, and the pellet dispersivitywas good. Sodium polyacrylate（PAAS）and sodium hexametaphosphate（SHMP） were used as chemical dispersants on theDegussa P25nano-TiO₂.The dispersion of the TiO₂particles and the stability of theslurry were best when the dosage of PAAS accounts for0.065%quality of TiO₂andSHMP accounts for0.09%quality of TiO₂. Silane coupling agent KH570was used forthe modification of Degussa P25nano-TiO₂. Under the test conditions of pH value from4.0to4.5and temperature70°C for5h, the KH570has successfully grafted onto thesurface of nano-TiO₂particles and the hydrophobized achieved the best when the massof KH570reached45%of TiO₂.The nano-TiO₂obtained from hydrothermal synthesis, dispersion and modificationwere prepared as a certain concentration of slurry and sprayed on the surface of thecoating to get nano-coatings with different water sensitivity. The contact anglemeasurement was used to characterize the water contact angle of nano-coating. Theresults showed that the nano-coatings of TiO₂made by hydrothermal synthesis can getthe water contact angle of18.3°and95.3°, the nano-coatings of P25TiO₂made bydispersion and modification can get the water contact angle of21.9°and92.1°.The contamination resistance of exterior wall coatings modified by nano-TiO₂was detected.It was shown that the contamination resistance of hydrophobic nano-coating was betterthan hydrophilic nano-coating.The artificial accelerated aging instrument was used to detect the ageing resistanceof exterior wall coatings modified by nano-TiO₂. The results showed that during theaccelerated aging process TiO₂particles can adhere to the surface of the coating andkeep the water sensitivity unchanged. At the same time, the nano-coatings can improvethe anti-aging properties of exterior wall coatings.