Effect of Pseudomonas putida on the degradation of epoxy resin varnish coating in seawater

• Pseudomonas putida decreased the corrosion resistance of the epoxy resin coating.
• Pseudomonas putida promoted the extensive corrosion on the steel substrate.
• Pseudomonas putida caused some pulverization and tiny holes on the coating.
• Pseudomonas putida degraded the coating mainly by changing the COH bond.
• The hydroxyl oxidation could be related to the degradation by Pseudomonas putida.

It is known that microorganisms degrade many materials. However, very little is known about the biodegradation of marine coatings. In this study, we explored the degradation of epoxy resin varnish coating in sterile seawater and seawater inoculated with Pseudomonas putida by the coating permeability analysis, electrochemical impedance spectroscopy, contact angle test, scanning electron microscopy, Fourier transform infrared spectroscopy. The decrease in the corrosion resistance of the coating was significantly higher in seawater inoculated with Pseudomonas putida than in sterile seawater between 48 h and 25 days of coating immersion. The extensive under-coating corrosion appeared on the substrates in both seawater systems, but the corrosion in seawater inoculated with Pseudomonas putida was much more serious. These results suggested that Pseudomonas putida significantly decreased the corrosion resistance of the coating and might decompose the coating. Some pulverization and tiny holes were found on the coating in seawater inoculated with Pseudomonas putida. Moreover, the absorbance of the COH peak for the unimmersed coating and the coating immersed in sterile seawater was significantly higher than that for the coating immersed in seawater inoculated with Pseudomonas putida. The results proved that Pseudomonas putida degraded the coating. The degradation could involve the hydroxyl oxidation.