Electrolyte permeation through photo-cured acrylic polymers on steel as related to corrosion of the substrate

The effect of 1,2-diphenyl, 2,2-dimethoxy, ethanone as photoinitiator in some ultraviolet radiation-cured acrylated acrylic formulations on steel was studied. Correlation between corrosion rates, measured with ASTM D610 standardized method, and electrolyte permeation through coatings, measured with ³⁶Cl-labelled 0.25 M NaCl solutions at 25°C, was systematically investigated. The length of time necessary for the complete failure of the coatings, as observed by the extension of corrosion products over the entire surface, was evaluated by visual inspection of corrosion or by the breakthrough curve of permeation, and found to be a function of photoinitiator concentration. The slight difference between failure time obtained by the two methods may well be due to a time lag between the activation of corrosion cells over the whole surface and onset of visible corrosion products everywhere. This time lag may be correlated to the protective value of the coating, and to its permeation properties, particularly.