Eco-friendly solvent-free synthesis of coumarin-based epoxy coatings for enhanced corrosion resistance and mechanical performance

Coumarin derivatives were synthesised via a rapid, solvent-free one-pot melt route that avoids long reactions, toxic solvents and expensive catalysts. The chemical structure of synthesized coumarin derivatives was established using IR, 1H NMR, 13CNMR and mass spectral data. Among the synthesized coumarin derivatives, C3 exhibited effective hardening behavior during epoxy curing, while C4 contributed antibacterial activity. These compounds were incorporated into bisphenol-A epoxy and applied on mild carbon-steel (ST-37) panels to assess their multifunctional performance. Dynamic mechanical analysis showed C3 raises storage modulus and Tg by ~ 40%, while agglomerated C4 lowers modulus 30% yet offers superior impact strength. Both coatings reached cross-cut adhesion 5B, > 2 kg pencil hardness and full mandrel flexibility. Antibacterial tests achieved > 90% killing of E. coli and S. aureus. Electrochemical impedance and 1000 h salt-spray (ASTM B117) revealed 92% lower corrosion current and durable barrier resistance, confirming exhibiting a synergistic effect in both structural reinforcement and microbial inhibition. The solvent-free process, low cost and easy formulation compatibility position coumarin-modified epoxies as sustainable, multifunctional industrial coatings that unite mechanical reinforcement, biocidal action and long-term corrosion protection in a single eco-friendly layer. solvent-borne zinc or chromate primers in mobility and infrastructure applications. Solvent-free green synthesis of coumarin derivatives completed in under 5 minutes with excellentyields. Coumarin 3 enhanced epoxy stiffness by 40%, while Coumarin 4 improved thermal stability andchar residue. Epoxy coatings with Coumarin 4 showed superior corrosion resistance, outperforming Coumarin3 systems and blank. Eco-friendly coatings demonstrated strong resistance to water, acids, and solvents with minimalenvironmental impact. DFT analysis confirmed Coumarin 4’s higher reactivity and potential as a sustainable corrosioninhibitor.