INFLUENCE OF THE PHOTOOXIDATIVE DEGRADATION ON THE WATER BARRIER AND CORROSION PROTECTION PROPERTIES OF POLYESTER PAINTS

The barrier properties of a paint are strongly influenced by the prese nce of defects, by photo-oxidative phenomena and by the adhesive prope rties of the polymer-metal interface. Impedance spectroscopy is a flex ible and efficacious instrument for assessing all these phenomena and is useful in supplying information on the mechanisms of deterioration as well as assessing the physical parameters associated with it. The w ide use of paints in external environments that are exposed to the eff ects of solar radiation and humidity makes the study of the deteriorat ion of organic coatings under these conditions important. The coeffici ents of humidity diffusion and the values of permeability and saturati on for different ultraviolet (u.v.) radiation intervals have been calc ulated, starting from the impedance data and using appropriate models. The relationship is shown between these values and the effective long -term properties of protection from corrosion of the paints. Copyright (C) 1996 Elsevier Science Ltd