Influence of water on the photooxidation of KHJ phenoxy resins, 1. Mechanisms

This study is devoted to the influence of water on the mechanisms of photooxidation of anticorrosion coatings based on epoxy resins used in extremely aggressive media like the marine environment. The two principal environmental parameters to be considered are sunlight (UV-light) and water. It is important to understand the role of these two environmental parameters on the ageing of epoxy anticorrosion coatings. On the basis of the effect of photooxidation on the molecular structure under “dry” conditions, water was introduced into the ageing process with either alternating cycles of irradiation/immersion in water or simultaneously by irradiation of the polymer in water. The presence of water had two effects on the photodegradation of PKHJ^® phenoxy resin; the first one was on the degradation of the main photoproduct (phenyl formates) formed during irradiation through a hydrolysis reaction leading to the release of formic acid. The second effect consisted of an increase in the photooxidation rate by the formation of photo-initiators.