Influence of phthalocyanine pigments on the photo-degradation of alkyd artists' paints under different conditions of artificial solar radiation

The influence of selected blue and green phthalocyanine pigments on the stability of alkyd paints exposed to accelerated solar radiation is presented. Thus, paint samples were artificially aged by exposure to accelerated solar radiation, including UV-B range. The ageing was performed with Xenon Arc lamp at low (soft conditions) and at high (strong conditions) irradiance values, where the soft conditions are comparable to natural light ageing. The behaviour of alkyd paints exposed to artificial ageing was investigated after two and four months by Attenuated Total Reflection Infrared Spectroscopy (FIR-ATR) and Thermally assisted Hydrolysis and Methylation Gas Chromatography/Mass Spectrometry (THM-GC/MS). It could be determined that the photo-degradation of the paints started already after two months of exposure under soft conditions. Paints aged under strong conditions showed comparable results when exposed for two and for four months. This indicates that samples are already highly damaged after the first two months of strong ageing and during additional two months no significant increase in photo degradation occurs. The results showed that - independently from the ageing conditions-in both cases the ester bond of the polyester portion of the alkyd resin is affected by photo-cleavage and the presence of phthalocyanine pigments is stabilizing the paint systems against it. Nevertheless, among the tested samples, the paints containing chlorinated and brominated copper phthalocyanine green (PG36) were the most degraded. (C) 2016 Elsevier Ltd. All rights reserved.