A commercial coating was transformed into a self-healing coating by inserting urea-formaldehyde microcapsules (MCs) containing tung oil (TO), to improve coated metal corrosion resistance.
The microcapsules were characterised regarding their morphology and chemical composition, and the presence of tung oil as core material was also proven by FTIR analysis. MCs were then incorporated into the matrix of a commercial mono-component alkyd coating, being added in the same proportion as the corrosion inhibitor (zinc phosphate) present in the original commercial coating.
Corrosion resistance was evaluated by the comparison between samples coated with an original commercial coating, commercial coating without zinc phosphate and a commercial coating containing MC., employing a corrosive saline medium of NaCl 3.5 % (w/w), where were carried out the electrochemical analysis of open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). For this, the stimulus-responsive capacity of microcapsules was proven through mechanical disruption.
Increased barrier properties
The results of the OCP and EIS tests showed that the microcapsules in the coating matrix caused a beneficial increase in barrier properties. Additionally, MC additive coating protected the metallic substrate when it suffers a mechanical defect through the release of the oil and its active protection conditioned to the self-healing effect.