SELF-HEALING PROTECTIVE COATINGS BASED ON EPOXY-LOADED POLYMERIC MICROCAPSULES

Protective coating failure can lead to excessive substrate wear, thus increasing the need for maintenance. Self-healing systems can offer autonomous crack repair and increase a coating’s service lifetime. Polymeric microcapsules (MCs) containing healing agents can be used in that perspective and exhibit significant potential. In the case of micro-cracks, microcapsules are ruptured and the healing agent flows into the crack. The released agent comes into contact with the catalyst that is also embedded in the matrix and is polymerized, bonding the crack faces, increasing the coating service lifetime and protecting the substrate from corrosion with significant benefits for industrial applications, such as marine. Epoxy-loaded microcapsules with a poly(urea-formaldehyde) shell were successfully prepared within the current study using one-step in situ polymerization based on the work of Tzavidi et al. (Journal of Applied Polymer Science, 2020). Microcapsules were obtained as a colorless free-flowing powder with a diameter of 37 μm and 78 % encapsulation efficiency (ratio of encapsulated substance to microcapsule mass). In order to study the self-healing properties of the microcapsules, they were dispersed in a commercially available alkyd-based paint at a content of 5, 10, or 15 % wt. along with the catalyst. Steel specimens were coated using a paintbrush with either an MC-loaded paint or pure paint as reference. A scratch was manually made on the coating with a blade, and electrochemical impedance spectroscopy (EIS) was used to evaluate the self-healing properties of the coating before and after the scratch. Based on the EIS tests, the MC-containing coating was found to offer corrosion protection even in the case of the low 5 % wt. microcapsule content.