Effect of graphene incorporation on properties of epoxy-based self-healing coatings

In this study, self-healing coatings based on epoxy resin with microcapsules were prepared by in situ polymerization and then tested. First, the microcapsules were synthesized and dispersed in the epoxy resin. The prepared microcapsules were characterized by Fourier transform infrared spectroscopy, which showed the successful encapsulation of linseed oil in urea-formaldehyde. During the synthesis of the microcapsules, the stirrer speed was adjusted to three levels: 300, 600, and 900 rpm. It was found that the particle size distribution of the microcapsules became narrower with increasing stirrer speed. The surface morphology of the coating was studied by scanning electron microscopy and optical microscopy, which show that the microcapsules are spherical and have a particle size distribution of 4–250 microns. Due to the poor mechanical properties of microcapsules, the epoxy resin containing microcapsules exhibits low mechanical properties. To improve the mechanical properties of the resulting coating, graphene nanosheets (GNs) were added to the epoxy resin. X-ray diffraction and transmission electron microscopy were used to investigate the dispersion of GNs in the matrix. Salt spray and tensile tests were performed to evaluate the corrosion and mechanical properties of the coating. Design-Expert software was used to design the experiments, and response surface methodology graphs generated by the software were used to analyze and predict the mechanical properties of the coatings with different microcapsule and GN weight fractions. It was found that the epoxy coating consisting of microcapsules (1–1.5 wt%) and GNs (0.26 wt%) gave the best results in terms of corrosion and tensile properties at speeds of 300, 600, and 900 rpm. This study shows that the agitation speed and the addition of GNs could play a crucial role in developing self-healing coatings in terms of strength, modulus, and corrosion protection.