Microcapsule based self-healing systems in anticorrosive epoxy coatings

In the present study, a new self-healing epoxy coating system for corrosion protection having microcapsule (MC) has been produced. The superiority of the present system evolves from the utilization of the environmentally friendly drying oils as Linseed oil and Tung oil and their alkyds for the healing agents instead of commonly used ones which necessitate the use of catalyst. This study involves the determination of urea-formaldehyde reaction conditions to produce an appropriate poly(urea-formaldehyde) resin for the shell structure of the MCs. Thereafter the encapsulation by means of in-situ polymerization has been studied with the parameters as the effect of medium pH, the amount of NH4Cl and resorcinol couple, the type and amount of surfactant and the type and rate of stirring. Optical microscopy (OM) has been utilized to follow the reaction. FTIR and NMR techniques have revealed the structure of MCs. TGA and SEM analysis has been utilized, as well. The models obtained employing an experimental design program revealed that capsules of 50 to 300 µm diameter produced using PVA as surfactant 20 to 60 mL. Furthermore, the capsules have been embedded in epoxy resin and then epoxy films and coatings have been characterized. The incorporation of capsules into the epoxy matrix results in decreasing of water vapor permeability (WVP) and adhesion strength. Electrochemical impedance spectroscopy (EIS) studies revealed that the charge transfer resistance of coating which is a measure of corrosion resistance increases as well. The self-healing efficiency of the epoxy coatings were between 53 and 78% .