THE DURABILITY OF WATER-BORNE ACRYLIC COATINGS

The influence of manufacturing and processing parameters on the environmental stability of aqueous acrylic-based latices is examined. A number of physical and chemical techniques were used to monitor the photochemical and thermal degradation of these latices. These are based on emulsion polymerised formulations of methyl methacrylate and butyl acrylate. In the first instance, acrylic latices based on different formulations were chosen as homopolymers and copolymers. Here, the nature of impurities and oxidation products generated during their manufacture are characterised and related to their influence on subsequent degradation. This involves the use of reflectance FT-IR spectroscopy to show functional group changes together with colourimetric UV analysis to determine photochemical generation of hydroperoxides. Early chemical changes and their subsequent influence on the physical and chemical properties of the latices during the latter stages of degradation are found to exhibit a close relationship. Thermal methods of analysis were also used to characterise differences in the properties of the latices before and during thermal degradation. To date, the nature of the residual persulphate initiator and the composition of the latex in terms of end-group modification are important parameters. Hydroperoxides are found to be important species during latex degradation, while the addition of low levels of co-monomer to the emulsion gave latices with improved photostability.