Study of the Water Barrier Properties of Paints After Natural and Accelerated Photooxidative Degradation

Abstract

The evaluation of the corrosion protection properties of organic coatings is often obtained by the exposure of coated samples to natural environment (for example, marine or industrial atmosphere) and by accelerated weathering tests (salt spray fog, UV irradiation, cycles, etc.). At the end of the test, however, the visual observation of the tested samples, comparing the coating appearance with defined standards, is currently the only checking system. Such procedures generally take a long time and the results are influenced by operator judgment; therefore, they are not completely objective. For this reason, the use of quantitative analysis, for example, EIS (electrochemical impedance spectroscopy) or FTIR can provide information on physical and chemical properties of the coating and on the corrosion process, allowing an early evaluation of the degradation phenomena. In this work the effects of natural UV degradation after exposure for several years in the atmosphere are compared with the consequences of artificial weathering in an UV chamber (ASTM G53) using electrochemical, infrared and calorimetric techniques. The comparison shows the remarkable differences in the two degradation mechanisms giving information on future developments for new testing procedures.