Electrosprayed PMMA microcapsules containing green soybean oil-based acrylated epoxy and a thiol: a novel resin for smart self-healing coatings

Abstract

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 μm 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.