Biobased curing agents with intrinsically reversible bonds for recyclable epoxy thermosets: A review

The integration of reprocessable and sustainable components into polymeric thermosets is gaining significant attention due to increasing regulatory demands and the urgent need to reduce CO₂ emissions. To advance sustainable development, efforts are being directed toward the design of biobased polymeric systems with competitive performance. Despite limitations in cost, durability, and large-scale applicability, these challenges can be addressed by next-generation bio-feedstocks that exhibit thermoset-like thermal and mechanical performances and thermoplastic-like reprocessable and repairable characteristics. This review highlights recent progress in developing curing agents with reversible covalent chemistries derived from renewable resources such as vegetable oils, cellulose, lignin, vanillin, syringaldehyde, quercetin, rosin, and protocatechualdehyde. These developed bio-derived curing agents have been applied to cure conventional and emerging epoxy monomers, demonstrating advances in curing efficiency, recyclability, and overall material performance. Furthermore, we compare metrics used to evaluate reversibility (reprocessing recovery, healing efficiency, stress relaxation), outline processing and characterization best practices, and highlight application areas (coatings, adhesives, composites). Finally, challenges, opportunities, and future directions are discussed, underscoring the potential of biomass-derived curing agents and innovative chemical strategies to enable sustainable epoxy thermosets for industrial applications.