Thermal analytical study of the oxidative stability of artists' alkyd paints

Abstract

Artists' alkyd paints are relatively new in the art world and were introduced in the 1970s. Since they are so new, little is known about their ageing properties and behaviour in the conservation field. Thermal analyses, specifically, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), were used in this work to study the changes in properties of artists' alkyd paint films with age. Both techniques revealed changes in the thermal properties as the films increased in age. The cross-linking rate during accelerated photo-ageing was observed with DSC by monitoring the exothermic reaction after the decomposition of peroxide groups, which form during auto-oxidation of the alkyd resin. The investigation of naturally aged films, some up to 28 years, revealed an increase in the glass transition temperature with age. TGA studies of naturally aged films indicated an increase in film density with age, probably due to cross-linking at first and then the possible formation of oxidative degradation products over time, such as carboxylate salts.