A kinetic investigation into the effect of stabilisers on the photo-oxidation of water based silica acrylic-based coatings

Abstract

Benzotriazole, triazine and hindered piperidine stabilisers have been incorporated into a copoly-methyl methacrylate/butylacrylate film that contains silica as a matting agent in order to investigate the effect of the stabilisers on photo-oxidation. The mode of addition of the stabilisers have also been examined by comparing their effects when directly added into the acrylic lacquer formulation and when first pre-adsorbed onto the silica before incorporation into the lacquer system. The photo-oxidation process was accelerated by irradiating the films in a Microscal unit (500 watt high pressure Hg/W source; λ>300 nm) and the rate of this photo-oxidation was followed using reflectance FT–IR spectroscopy to monitor changes in the concentration of key functional groups. Scanning electron microscopy was also used to examine changes in the physical appearance of the films. This study showed that the acrylic films with silica containing preadsorbed stabilisers are stabilised more effectively than those silica films containing directly added stabiliser. They also highlight the fact that the mode of addition of the stabiliser plays a significant role in the degree of stabilisation and that this, in turn, depends upon the type of functional group produced during photooxidation. Hydroxyl growth, de-esterification and vinyl group transformations were impaired by the preadsorbed silica based stabilisers. From the SEM analysis stabiliser preadsorption appeared to prevent oxidation of the acrylic matrix at the silica particle surface.