Design of Thermoplastic and Few-Layer Graphene Modified Epoxy Coatings With Semi-Interpenetrating Polymer Networks for Hydrogen-Bond Mediated Self-Healing and Mechanical Performance Enhancement

Abstract

The growing demand for durable protective coatings in harsh environments has intensified interest in self-healing epoxy systems, which autonomously repair damage and extend service life. However, conventional epoxy coatings lack intrinsic self-healing functionality and are prone to damage. Thermoplastic modification, though effective in imparting self-healing, often compromises the mechanical strength, limiting broader applicability. In this study, epoxy is modified with polycaprolactone (PCL) and polyethylene glycol (PEG), facilitating the formation of a semi-interpenetrating network (semi-IPN), enabling reversible hydrogen bonding and shape memory behavior. The coating demonstrates a healing efficiency of 87% after 1 h of heat treatment. To overcome the associated decline in stiffness, graphene synthesized by microwave expansion is introduced as a nanofiller. The optimized Epoxy/Polycaprolactone/Polyethylene glycol/Graphene composite system with 0.075 wt% graphene achieved improved tensile strength (48.9 MPa) and outstanding healing efficiency (~92% at 80°C for 1 h). Electrochemical Impedance spectroscopy further confirmed the self-healing and anti-corrosive performance, with an outstanding inhibition efficiency (P_i) of 96.13%, charge transfer resistance of 8.73 × 10⁵ Ω·cm², and an impedance modulus of 8.2 × 10⁸ Ω·cm². These results establish the synergistic combination of thermoplastic modifiers and graphene as a promising route to design robust, multifunctional durable coatings with self-healing and corrosion resistance.