Eugenol-Based Epoxy Materials with High Biobased Carbon Content and Their Structure–Property Relationships

In order to reduce dependence on petroleum resources, three different biobased epoxy monomers (Eu-EP-1, Eu-EP-2, and Eu-EP-3) with a biobased carbon content of 76.9%–83.3% were prepared from eugenol, which can be derived from lignin. Three eugenol-based epoxy thermosets (Eu-EP-1/IPDA, Eu-EP-2/IPDA, and Eu-EP-3/IPDA) were then obtained by curing Eu-EP monomer with a commercial IPDA (isophorone diamine) hardener; the curing activation energy was in the range of 37.4–48.2 kJ/mol, the gel content ranged from 95.4%–96.5%, and the cross-linking degree reached 1185–2119 mol/m3, confirming that Eu-EP and IPDA were cured to form cross-linking network structures. Therefore, the Eu-EP/IPDA thermosets had excellent in-service performance with a Tg of 63.9–76.3 °C and a tensile strength of 34.7–43.1 MPa. However, the Eu-EP/IPDA thermosets with permanent chemical bonds were difficult to recycle. Since Eu-EP-2/IPDA had balanced performance, Eu-EP-2 was selected to develop recyclable Eu-EP/AFD epoxy vitrimers by curing with AFD (4,4′-dithiodiphenylamine). The resulting Eu-EP-2/AFD1.00 epoxy vitrimer had a Tg of 79.4 °C and a tensile strength of 39.2 MPa, and the remodeling of the Eu-EP-2/AFD1.00 epoxy vitrimer could be achieved by hot pressing at 200 °C for 6 h; the self-healing of the scratched material could be achieved by heating at 180 °C for 2 h, and the Eu-EP-2/AFD1.00 epoxy vitrimer could be dissolved in mercaptoethanol. Therefore, Eu-EP is a potential sustainable epoxy monomer for the development of epoxy materials with a balanced in-service performance and recyclability. This study offers a facile solution for the development of sustainable eugenol-based epoxy materials.