Aging behaviors of acrylic polyurethane coatings during UV irradiation

UV accelerated ageing was performed on acrylic polyurethane anticorrosive coatings; gloss and color difference testing, SEM and FTIR analysis incorporated with EIS were used to analyze their photoaging behavior. The results indicate that the photoaging of acrylic polyurethane coatings can be sensitively detected by gloss measurement; on the basis of contact angle and color difference, there are three processes during the photoaging of acrylic polyurethane, i.e. prophase (slow photoaging), metaphase (quick photoaging) and anaphase (slow photoaging). The chemical changes of the coatings show that UV irradiation causes the breaking of O—CH and C—N bands, which is considered the main reason of acrylic polyurethane photodegradation. Compared the results of surface analysis with those of EIS, it can be found that the corrosion resistance of acrylic polyurethane has declined obviously before visible photodegradation.