THE DURABILITY OF WATER-BORNE ACRYLIC COATINGS

The influence of manufacturing and processing parameters on the enviro nmental stability of aqueous acrylic-based latices is examined. A numb er of physical and chemical techniques were used to monitor the photoc hemical and thermal degradation of these latices. These are based on e mulsion polymerised formulations of methyl methacrylate and butyl acry late. In the first instance, acrylic latices based on different formul ations 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 degrada tion. This involves the use of reflectance FT-IR spectroscopy to show functional group changes together with colourimetric UV analysis to de termine photochemical generation of hydroperoxides. Early chemical cha nges and their subsequent influence on the physical and chemical prope rties of the latices during the latter stages of degradation are found to exhibit a close relationship. Thermal methods of analysis were als o used to characterise differences in the properties of the latices be fore and during thermal degradation. To date, the nature of the residu al persulphate initiator and the composition of the latex in terms of end-group modification are important parameters. Hydroperoxides are fo und to be important species during latex degradation, while the additi on of low levels of co-monomer to the emulsion gave latices with impro ved photostability.