Determination of Molecular Interactions between Copper Pigments and Soybean Oil Alkyd Resins in Paints: A...

Alkyd paints are widely used in modern painting and can be obtained commercially or prepared from pure materials. Various formulations can be used to obtain these paints. Copper pigments can be found in various works of art and in industrial paints. The use of these pigments in modern resins can be a low-cost alternative for different applications. However, studies must be conducted to ensure safety when applying these paints. In this work, the interaction of Cu-(II) present in malachite, azurite, and copper acetate pigments with soybean oil-based alkyd resins when subjected to heat treatment above 50 °C was characterized. The results show that paintings containing malachite and azurite exhibited colorimetric ΔE values of 2.77 and 3.72, respectively, showing no significant chromatic change during the studied heat period. Fourier transform infrared (FTIR) spectroscopy revealed a decrease in the intensity of ester and phthalic groups in the resin over time, indicating that reactions occurred in these groups during the sample aging process. Raw copper acetate was initially present in the dimeric form; however, when mixed with a binder, monomeric species were formed, and the intensity of dimers decreased with the aging period, leading to the formation of only monomeric species with a color change. Scanning electron microscopy (SEM) analysis showed that the paint layers remained uniform even after the studied aging period. μ-Raman showed signals below 500 cm^-1, which are attributed to Cu-O vibrational modes of new structures formed during the aging process of the paints. The chemical transformations do not lead to color changes in the pigments of malachite and azurite, so the results suggest that soybean oil-based alkyd resin could be a viable and cost-effective alternative to be used in the formulation with copper pigments. Furthermore, the data present can help understand the behavior of alkyd paints in the presence of copper pigments, assisting in the advancement of materials for use in painting materials.