Thermal analysis of the interaction of inorganic pigments with p(nBA/MMA) acrylic emulsion before and after UV ageing

Differential scanning calorimetry (DSC) and thermogravimetry (TG) analyses were used to investigate the influence of inorganic pigments on the photo-oxidative stability of an acrylic emulsion binding medium. For this purpose, three different types of inorganic pigments such as ultramarine blue, cadmium red and hydrated chromium oxide green were selected and mixed with an acrylic emulsion binding medium of poly(n-butyl acrylate/methyl methacrylate). These laboratory mixed paints were analysed before and after UV exposure for different periods of time. In addition, three acrylic commercial paints such as ultramarine blue, cadmium red and chromium oxide green from Liquitex_ and Rembrandt_ companies were also analysed. The results obtained with both thermal techniques suggested that ultramarine blue has the strongest influence on the photo-oxidative stability of the binding medium. A higher increase of the glass transition temperature Tg was observed by DSC analysis on the UV aged binder mixed with ultramarine blue. This result was confirmed by the TG investigations that showed a gradual decrease of the initial temperature of degradation as well as the strongest decrease of the final mass% of the organic compounds. Similar results were measured from the Liquitex_ and Rembrandt_ blue paints. Keywords: Acrylic emulsion, Inorganic pigments, Ultramarine blue,UV ageing, DSC, TG