New strategy to assess the performance of organic coatings during ultraviolet–condensation weathering tests

• Published in: Electrochimica acta Vol. 124; pp. 119 - 127
• Main Authors: Bedoya, F.E., Gallego, L.M., Bermúdez, A., Castaño, J.G., Echeverría, F., Calderón, J.A., Maya, J.G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-04-2014
• Subjects: Chlorination; Coatings; Corrosion prevention; Electrochemical analysis; Electrochemical impedance spectroscopy; Electrochemical stress index; Organic coatings; Rubber coatings; Stresses; UV–condensation weathering test; UV–condensation weathering test; Organic coatings; Electrochemical stress index; Electrochemical impedance spectroscopy
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2013.09.064

•Long term cyclic tests sometimes are not enough to assess organic coating performance.•Changes in electrochemical properties within a cycle correspond to poor performance.•A stress index (ES) was calculated from EIS measurements for UV–condensation test.•ES index can provide a quick method to compare coatings subjected to cyclic tests.
In this research the evolution of the electrochemical properties of five commercial anticorrosion coatings (3 alkyds systems, 1 polyurethane system and 1 chlorinated rubber system) was investigated using ultraviolet–condensation (UV–condensation) exposure in accordance with ASTM D4587 and electrochemical impedance spectroscopy (EIS). It was observed that for the modified zinc-rich alkyd and chlorinated rubber coatings a time of 4800h of exposure to a UV–condensation cyclic test was not long enough to assess and distinguish their anticorrosion performance. The high protective capabilities of these coating systems results in an absence of significant visual detriment and few changes in their electrochemical properties along time. Thus, a different approach is proposed aimed to assess the performance of organic coatings using EIS measurements within a single cycle of UV–condensation, therefore they could be compared between them effectively and quickly. Fourier transform infrared spectroscopy (FT-IR) and complementary assays such as salt spray, Prohesion and humidity tests were used to validate the results obtained with the proposed method. Findings reveal that the change in electrochemical properties for a single cycle corresponds to poor performance during long term exposure. Finally, an electrochemical stress index is proposed in order to evaluate the stress caused to the coating when it is exposed to cyclic tests.