Effect of crosslinking density on the self-healing and self-reporting properties of epoxy anti-corrosion coatings

This work developed a novel coating with self-healing and self-reporting performance by embedding polyurethane/poly-(urea-formaldehyde) (PU/UF) microcapsules in a shape memory epoxy polymer. 2'7'-Dichlorofluorescein (DCF) and linseed oil were applied as the coloring agent and healing agent, respectively, which are encapsulated into the PU/UF microcapsules (DL@PU/UF microcapsules) via a facile one-step method. To adjust the shape memory effect and the self-reporting performance of epoxy system, two kinds of curing agents (D230 and D400) were reacted with bisphenol A diglycidyl ether epoxy monomer to design a series of coating samples, finally the optimal coating system was selected by three indexes including barrier performance, residual amino content and coating hardness. When the composite coating was damaged, DCF can flow out of the broken microcapsules and react with the residual amino groups in the epoxy coating matrix, which can be recognized red signals in natural light and yellow fluorescent signals under ultraviolet light irradiation. More importantly, the excellent self-reporting property of the coating can be achieved on various metal substrates that broaden the application range of the coating. As for self-healing performance, the damaged coating can be healed quickly due to the shape memory effect of the coating as well as the filling of linseed oil in the scratched region. The Rctvalue of the healed coating containing 6 % DL@PU/UF microcapsules after immersing in 3.5 wt% NaCl solution for 5 days was more than 3 times that of the scratched coating, and the Rc value was about 16 times that of the scratched coating, indicating its corrosion protection performance. The novel coting not only achieve timely selfreporting ability of color and fluorescence, but also rapidly repair the coating damage, which is essential to practical applications.