Harnessing Eugenol for Sustainability: Synthesis and Characterization of Biobased Epoxy Thermosets

In this study, biobased epoxy networks were developed from a bis-eugenol epoxy monomer (B) cured with natural carboxylic acids such as citric acid and itaconic acid (IA) and with synthetic amine Jeffamine D230 (D). Differential scanning calorimetry revealed distinct curing behaviors governed by the functionality and structure of the cross-linkers. The IA-cured network showed dual reactivity through its α,β-unsaturated double bond, leading to additional cross-linking at elevated temperatures. Fourier transform infrared spectroscopy confirmed complete epoxy conversion via esterification or amino-addition mechanisms, while thermogravimetric analysis demonstrated high char yields and no solvent residues, indicating excellent thermal stability and potential flame-retardant behavior. Dynamic mechanical analysis revealed glass transition temperatures of 48-56 °C and gel contents above 96%, confirming full curing and dense cross-linked structures. Surface analyses showed tunable hydrophilicity and improved antibacterial activity for acid-cured systems. Degradation and XPS studies further highlighted that the chemical nature of the cross-linker dictates stability under corrosive environments. Amine-cured networks degrade via C-O cleavage in aqueous and alkaline media, whereas acid-cured systems resist oxidation but undergo ester hydrolysis under basic conditions. These findings demonstrate that eugenol-based thermosets can serve as eco-friendly, corrosion-resistant coatings with adjustable flexibility and high renewable content.