One of the approaches to prolong the service lifespan of polymeric material is the development of self-healing ability by means of embedded microcapsules containing a healing agent. In this work, poly(melamine-urea-formaldehyde) (PMUF) microcapsules containing a palm oil-based alkyd were produced by polymerization of melamine resin, urea and formaldehyde that encapsulated droplets of the suspended alkyd particles. A series of spherical and free-flowing microcapsules were obtained. The chemical properties of core and shell materials were characterized by Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and proton nuclear magnetic resonance spectroscopy (¹H-NMR). Differential scanning calorimetry (DSC) analysis showed a glass transition around −15 °C due to the alkyd, and a melting temperature at around 200 °C due to the shell. Thermogravimetric analysis (TGA) results showed that the core and shell thermally degraded within the temperature range of 200–600 °C. Field emission scanning electron microscope (FESEM) examination of the ruptured microcapsule showed smooth inner and rough outer surfaces of the shell. Flexural strength and microhardness (Vickers) of the cured epoxy compound were not affected with the incorporation of 1%–3% of the microcapsules. The viability of the healing reactions was demonstrated by blending small amounts of alkyd with epoxy and hardener at different ratios. The blends could readily cure to non-sticky hard solids at room temperature and the reactions could be verified by ATR-FTIR.

For the first time, the binary components of a self-healing epoxy system was developed comprising of a green acrylated epoxy resin and its thiol-based curing agent encapsulated in a poly (methyl methacrylate) (PMMA) shell by electrospraying technique. The field emission scanning electron microscopy images revealed that the two microcapsules formed were almost spherical with rough and irregular surfaces. The average diameter of microcapsules ranged from 1.165 to 1.418 μ m for the two microcapsules. FTIR spectra and thermal analysis were used to investigate the encapsulation of acrylated epoxy resin and thiol curing agent in PMMA as well as the kinetics of crosslinking reaction between the two components. Based on FTIR spectra, the thiol curing agent was involved in the crosslinking reaction with the epoxy group (810 cm ⁻¹ ) and the C = C segment (1634 and 1613 cm ⁻¹ ) of acrylated epoxy resin. The DSC results indicated an exothermic peak (at 65 °C) proving that this system is efficient in self-healing epoxy resins for coating applications. Furthermore, the ability of epoxy coatings to protect the scratched coating substrate from corrosion media (the healing performance) without microcapsule, with dual microcapsules, single healing agent-containing microcapsule and single curing agent-containing microcapsule were also evaluated using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). The results were in line with the potentiodynamic polarization and the EIS. The highest self-healing efficiency (78%) was obtained for binary capsule concentration of 1%, indicating presence of sufficient amount of material to heal the cracks.