Influence of the photo-oxidative degradation on the water barrier and corrosion protection properties of polyester paints

The barrier properties of a paint are strongly influenced by the presence of defects, by photo-oxidative phenomena and by the adhesive properties of the polymer-metal interface. Impedance spectroscopy is a flexible 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 wide use of paints in external environments that are exposed to the effects of solar radiation and humidity makes the study of the deterioration of organic coatings under these conditions important. The coefficients of humidity diffusion and the values of permeability and saturation for different ultraviolet (u.v.) radiation intervals have been calculated, 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