The effects of HALS in the prevention of photo-degradation of acrylic clear topcoats and wooden surfaces

A study of the photocatalytic degradation of an acrylic dispersion based coating and its prevention using hindered amine light stabilizers (HALS) was carried out on solid films by exposing them to Xenon arc light. The degradation rates were compared using FTIR-ATR techniques by plotting the differential build up of the hydroxyl and hydroperoxide bands as function of exposure time. UV-Vis spectroscopic studies were carried out as well to obtain data about the light stabilization of organic UV Absorbers (UVA) and inorganic UV screeners by HALS. The effectiveness of an aqueous primer comprising a specific lignin stabilizing HALS in combination with clear topcoats with UVA or UV screeners in the prevention of photo-induced discolouration of wooden surfaces was investigated by measuring the colour change during exposure time. It was shown, that the usage of HALS was effective in reducing the degradation speed of clear coats with UVA and UV screeners. Results obtained by UV-Vis spectroscopic analysis during the exposure cycle showed an inhibition of the photo-degradation of the UVA themselves, while no positive effect occurred on inorganic UV screeners. A lignin stabilizer containing aqueous primer with a specific HALS as active component, showed some promising results in combination with transparent topcoats comprising organic UVA and inorganic UV screeners, except ZnO, where a strong antagonistic effect occurred.