Preparation of epoxy resin adhesives based on high phenolic nanomodified lignin particles.

Lignin, a renewable aromatic biopolymer derived from lignocellulosic biomass, has emerged as a promising candidate for sustainable epoxy resin adhesives. Nevertheless, condensed macromolecular architecture and structural heterogeneity in lignin limit phenolic reactivity and crosslinking efficiency of lignin-based epoxies. In this study, enhanced adhesion performance was achieved in a 100 % alkaline lignin-based epoxy adhesive，via effective demethylation and nanosizing to reveal more phenolic moieties. The resulting high-phenolic lignin nanoparticles (HPLNPs, 30 ± 5 nm diameter by TEM analysis) exhibited an 86 % increase in phenolic hydroxyl content (3.47 mmol/g vs. 1.86 mmol/g in pristine lignin). When directly epoxidized without additional chemical modification, the HPLNP-derived resin demonstrated exceptional adhesive performance, achieving a lap shear strength of 2.45 ± 0.12 MPa in wood bonding applications. Notably, the adhesive maintained 91.3 % of its initial strength following 72-h cold water immersion (2.24 ± 0.15 MPa retention), indicating robust hydrolytic stability. Comparative FTIR analysis revealed enhanced crosslinking density attributed to the increased phenolic moieties acting as active sites for epoxy-amine reactions. This study establishes a scalable strategy for enhancing the adhesive performance of lignin-based epoxies, while simultaneously advancing activation strategies for lignin valorization in bio-based functional materials.