Lignin-tannic acid epoxy resins based on dynamic covalent bonding of β-hydroxy esters with closed-loop recyclability, exceptional adhesive properties and excellent photothermal capacity.

This study addresses the waste of resources and environmental pollution associated with the use of traditional, non-recyclable, epoxy resins produced using petroleum-based products. Totally biomass-based epoxy resins (TPLs) have been developed by replacing bisphenol A diglycidyl ether with epoxide-modified tannic acid and replacing petroleum-based curing agents with carboxylate-modified lignin. Because of the incorporation of dynamic covalently bonded β-hydroxy esters, TPLs are suitable for closed-loop recycling. For example, one of the new epoxy resins (TPL-0.1) had an initial tensile strength of 26.1 MPa and retained almost all of this (80 %, 20.6 MPa) following closed-loop regeneration using a solvent mixture containing ethylene glycol and water (6:4). A second epoxy resin, TPL-0.05, which contains a higher proportion of lignin, showed remarkable versatility, not only achieving a shear strength of 12.4 MPa when used as an adhesive but also having excellent photothermal properties. TPL-0.05 has a photothermal conversion efficiency of 47.8 %, with surface temperatures reaching 120.5 °C under 1 kW·m irradiation. When used as a coating in a solar water heater, the water temperature increased from 20 °C to 55 °C within 10 min, representing a 340.7 % improvement in heating rate compared with an uncoated control. This research offers an innovative approach for developing recyclable, high-performance epoxy resins and promotes the sustainable advancement of epoxy resin technology through the high-value utilization of biomass resources and dynamic bond design.