Effects of nano-TiO2 and nano-SiO2 particles on the reflectance and weathering durability of solar heat reflectance coating

Abstract

Two pure emulsion acrylic resins, PRIMAL™ AC-261 and DIRTSHIELD™ K-2, were used to fabricate the multifunctional acrylic coating for solar heat reflective system. The ratios of nano-TiO2: micro-TiO2 particles were 2/98, 4/96, and 8/92, whereas the content of heat-reflective nano-SiO2 particles was 1 % by the total solid content of coating film.The experimental results showed that the appropriate ratio of nano-TiO2 /micro-TiO2/solid resin was 4/96/100, corresponding to the 2 % content of nano-TiO2 particles in the coating. At this optimal ratio, a 60 µm thick coating had an average refractive index of 92.68% in the 425–1400 nm range. Under solar irradiation, our synthesized acrylic nanocomposite coating showed a temperature reduction of concrete surface up to 9.5 °C. When the ambient air temperature was in the range of 40–42 °C, this coating sytem could reduce the temperature of concrete surface and test chamber by 9.5 °C and 4.2 °C, respectively. In case of neat acrylic coating system (without nano-TiO2 particles), it could only reduce the temperature of concrete surface and test chamber by 7.5 °C and 2.5 °C, respectively.After 1500 h of the accelerated weathering test, no blisters or peelings were observed by naked eyes for both coatings with or without nanoparticles. With nanoparticles, their reflectance index decreased slightly from 92.68% to 90.48%. Without nanoparticles, the refractive index decreased from 89.17% to 86.67%. These findings indicated that adding nano-TiO2 and nano-SiO2 particles to the acrylic coating formulation has significantly increased the reflectivity, cooling insulation efficiency, and weathering resistance of the coating.