Evaluación de la reflectancia solar total en recubrimientos con nanopigmentos híbridos tras envejecimiento acelerado UV

Abstract

Finding cool pigments, answered the market demand of energy saving building materials. The total solar reflectance (%TSR) parameter measured as a percentage, designate the level of thermal insulation of the coloring materials used in coatings. On the other hand, in the context of the generation of nanostructured hybrid pigments from organic dyes and inorganic nanoclays, we are looking to obtain resistant coloring materials to environmental conditions. In this work It was searched the obtaining of optimal nanopigments in terms of resistance to ultraviolet radiation, and also high value of %TSR for future applications in exterior coatings. As an added value was sought working with natural dyes. The application of natural dyes is limited precisely because of their low resistance to environmental conditions. Usually natural dyes are anionic in water solution, so we have worked also with an anionic synthetic dye. We decided to start with two red dyes: the natural beetroot extract (Col Napture Red LC313), and the synthetic dye, CI Acid Red 52. It was worked with two kinds of layered clay, the natural montmorillonite with cation exchange property, and the hydrotalcite with anion exchange capacity. Finally, in order to improve the adsorption properties of both clays, it was modified with two surfactants, the cetylpiridinium-bromide hydrate (CPB) for the montmorillonite clay, and the Sodium dodecyl sulfate SDS for the hydrotalcite clay. It was made an experimental design, with 23 factorial. We were choose to optimize the factors: color resistance to UV radiation, and the %TSR after aging tests. It was conclude that both nanoclays modified the TSR% value of both dyes, increasing it, especially the hydrotalcite. The selected nanoclay was the only significant parameter in TSR% value for the encapsulated organic dyes. Therefore it must be used hydrotalcite in order to obtaining cool pigments. The color degradation, measured as color difference AE*ab, is much lower in both dyes with the nanoclay encapsulation. In this case, the reinforcing effect is independent of the nanoclay selected, but the hydrotalcite was more effective, although the characterization results indicated that the dyes were not introduced into the nanoclay structure. Have been obtained very light colors with natural dye, but these colors were more resistant’s to the UV aging test, with the encapsulation in both nanoclays. If it was looking for cool nanopigments, it should be used the hydrotalcite.