The photooxidative degradation and stabilisation of water-borne acrylic coatings systems

The influence of manufacturing and processing parameters on the photooxidative stability of aqueous acrylic based latices is examined by FTIR and hydroperoxide analysis. These are based on emulsion polymerised formulations of methyl methacrylate and butyl acrylate. Here acrylic latices based on different formulations are chosen as home-polymers and copolymers. The nature of impurities and oxidation products generated during their manufacture are characterised and inter-related to their influence on subsequent photooxidative degradation. This involves the use of reflectance FT-IR spectroscopy to show functional group changes together with colourmetric U.V. analysis to determine the photochemical generation of hydroperoxides. The early chemical changes and their subsequent influence on the physical and chemical properties of the latices during the later stages of photooxidation are found to exhibit a close inter-relationship. To date the nature of the surfactant and the composition of the latex in terms of end group modification are important parameters. De-esterification and hydroperoxide formation are found to be important processes during latex photooxidation while the addition of low levels of, co-monomer to the emulsion give latices with improved photostability. While co-reactive hindered piperidine stabilisers are found to be effective the incorporation of simple terminal dialkyl acrylamide/methacrylamide groups are equally as effective. Oxygen scavenging via the formation of alkylamino radicals is disussed.