A recyclable and high-performance bio-based epoxy resin from industrial lignin

Lignin, a renewable biopolymer containing abundant phenolic hydroxyl groups (PhOH), was considered a promising candidate for replacing petroleum-based BPA in the epoxy resin process. To date, numerous studies were dedicated to synthesizing lignin-based epoxy resins from various lignins, such as organosolv lignin, enzymatic hydrolysis lignin, and lignin derivatives. However, there was still a lack of a simple, efficient, and environmentally friendly approach for producing lignin-based epoxy resins from industrial lignin. In this study, we reported a one-pot strategy for synthesizing lignin-based epoxy resin (LER) from industrial lignin (Kraft lignin: KL) (Mw = 27,960). KL was oxidized with hydrogen peroxide in an alkaline solvent, followed by reaction with epichlorohydrin. In addition, the oxidation of KL and the synthesis of lignin-based epoxy resin were successive without separation, which simplified the process and enhanced the yield of LER. Maleic anhydride (MA), a bio-based compound derived from renewable biomass, was used to cure LER to prepare bio-based thermoset (LER-MA) with good mechanical performance (tensile strength of 40.4 MPa). Furthermore, due to the abundance of ester bonds, LER-MA could be recycled using the alkaline solvent, and the tensile strength of chemically recycled LER-MA retained nearly 90 %. Beyond recyclability, LER was also applied as a wood adhesive with starch, achieving a dry shear strength of 1.66 MPa and a wet shear strength of 0.99 MPa. Taken together, our work offered a simple and effective method for producing sustainable, high-performance, and chemically recyclable alternatives to conventional thermosets. • Using lignin as a raw material can effectively utilize low-value biomass resources. • The one-pot strategy (oxidation and epoxidation) simplifies the process and boosts yield. • LER-MA was cured with 100 % lignin-based epoxy resin (BPA-free). • RE-LER-MA retains the tensile strength of 91 % after recycling. • Serves as a wood adhesive with high dry/wet strength meeting national standard.