Development of self‐healing coatings based on urea‐formaldehyde/polyurethane microcapsules containing epoxy resin

Abstract In this study, the synthesis of urea‐formaldehyde/polyurethane (UF/PU) microcapsules containing epoxy resin for self‐healing and anti‐corrosion coatings with good stability has been reported. Spherical microcapsules were prepared with a diameter of about 50–720 μm and a shell thickness of 0.6–0.7 μm via in situ polymerization in an oil‐in‐water emulsion using 2,4‐toluene diisocyanate‐based pre‐polymer along with the urea‐formaldehyde. Scanning electron microscopy (SEM) and optical microscopy (OM) were employed to evaluate the shape and morphology of the microcapsules. Fourier transform infrared (FTIR) spectroscopy showed the absence of free isocyanate groups within the microcapsule shell confirming the completion of shell formation reactions. OM illustrated that the microcapsules were stable over a period of 30‐days in toluene and xylene. Increasing microcapsule loading improved crack repairing and anti‐corrosion performance of the coating layer. Low‐carbon steel coupons coated with an epoxy resin containing 10 wt% microcapsules and scribed using a scalpel blade showed no visible sign of corrosion after up to 5 weeks of exposure in a standard salt spray test chamber.