Chemical composition of cool coatings and the influence on solar reflectance and thermal emittance

Resumo

Cool materials have higher values of solar reflectance and lower values of thermal emittance, although still high when compared to conventional coatings, thus, their surfaces are less heated. In this regard, the goal was to identify the chemical elements present on cool surfaces that influence solar reflectance and thermal emittance. To this end, the spectral reflectance and the thermal emittance were measured with methods and equipment standardized by the Cool Roof Rating Council (CRRC) of 23 elastomeric cool coatings commercialized in the Brazilian market, and the chemical composition of the surfaces with EDS (Energy-dispersive X-ray detector) coupled to the field emission scanning electron microscope (FE-SEM) was analyzed. The presence of the metallic chemical element (titanium) in greater quantities on the surfaces was not decisive for lower thermal emittance values. The surfaces of materials with lower carbon and higher oxygen content have higher near infrared and solar reflectance. Therefore, surfaces with a matte finish have higher solar reflectance values because of the higher ratio of pigments in relation to resin than those with a glossy finish, which are mistakenly associated with higher reflectance due to its high surface gloss.