Pigment power: a comparative study on the effect of different cadmium sulfide pigments on the curing of polyunsaturated drying oils

The present study investigates the effects of various cadmium-based pigments on the curing behaviour of linseed oil. Model linseed oil paints, prepared starting from different cadmium yellow pigments, were subjected to accelerated aging inside a thermobalance at 80 °C, under oxygen flow and in the dark. Thermogravimetric analysis (TGA) was used to monitor the mass change of the paint samples induced by oil autoxidation during curing, while ATR-FTIR spectroscopy provided insights into molecular transformations before and after thermal exposure. Results reveal that cadmium yellow pigments with identical chemical composition (CdS) can induce different curing kinetics, depending on the crystalline features of the pigments, namely crystallite size and degree of crystallinity. Pigments having nanocrystalline structures delayed the onset of peroxide propagation, resulting in extended induction times and incomplete polymer network formation in the timeframe investigated. These paints also showed formation of cadmium carboxylates and cadmium sulphates. These results may be related to the intrinsic peroxidase-like (POD-like) catalytic activity of nanocrystalline CdS, reported here for the first time in a non-aqueous medium.