PIGMENTOS INORGÂNICOS SINTÉTICOS À BASE DE ALUMÍNIO E PECTINA PREPARADOS VIA MÉTODO DE MISTURA SÓLIDA PARA APLICAÇÕES EM TINTAS IMOBILIÁRIAS

Abstract

This work consists in obtaining synthetic inorganic pigments, aiming at the application in commercial paints. White pigments were prepared by physically mixing an inorganic aluminum salt with a polysaccharide - citrus pectin and colored pigments were prepared by the addition of inorganic salts of cobalt, iron and nickel in a lesser amount to the previous mixture, through the stages of mixing, calcination (600 °C) and maceration. For comparison purposes, synthetic inorganic pigments were prepared without the organic part by the same synthesis process. All the pigments had their thermal, structural, morphological, spectroscopic, textural and colorimetric properties evaluated and in order to seek new properties for the pigments, antioxidant and antimicrobial activity was also studied. The organic and inorganic precursors used in the synthesis were characterized in terms of their thermal, structural and morphological properties. It has been observed that they may influence the pigment obtained at the end. The organic precursor has greater influence on the morphological properties and the inorganic precursor, allows to choose higher or lower calcination temperatures. The pigments prepared with citrus pectin and calcined at 600 ºC showed totally modified texture properties obtaining pigments with lower pore volume and surface area and larger pore size. The colorimetric study showed strong influence of the use of pectin in the synthesis for both the pigments in powder form and in the applied form, due to the total color difference (ΔE) obtained for each pigment pair evaluated. In addition, these pigments showed greater ease in dispersion in white paint than those without the organic part. The highest percentages of antioxidant activity were obtained for the pigments prepared with citrus pectin and the antimicrobial activity was also influenced by the polysaccharide, but the greatest influence came from the transition metals used. By increasing the calcination temperature (800 ºC and 1000 ºC) of the pigments prepared with citrus pectin, new coloring or shades were obtained. These changes occurred due to structural changes in the pigments. Obtaining crystalline phases with increasing calcination temperature generated materials with smaller amounts of residues or interferers, improving the degree of reflectivity in the near infrared region (NIR).