One-Step Synthesis\nof Waterborne Epoxidized Lignin\nNanoparticles with High Epoxy Value and Stability for High-Strength\nAdhesives

Lignin, being the most abundant renewable aromatic polymer,\nexhibits\nimmense potential in sustainable biobased epoxy adhesives. However,\nthe tedious preparation process and uncontrolled homopolymerization\nof epoxidized lignin hinder their large-scale production. Herein,\nwe propose a facile one-step strategy to synthesize a high-performance\nwaterborne lignin-based epoxy adhesive based on the high selectivity\nof the phenol-epoxy reaction. Owing to the acidity difference between\nphenol and aliphatic hydroxyl, the phenolic hydroxyl groups in lignin\ncan be preferentially initiated with epoxy groups, which inhibit the\nreaction on polyglycidol chain propagation. The resulting epoxidized\nlignin nanoparticles (ELNPs) feature nanoscale (150–250 nm),\nlow molecular weight, and high epoxy value (∼3.84 mmol g<sup>–1</sup>). The ELNP colloidal dispersions possess high zeta\npotentials (−34.20 mV) and impressive long-term storage stability\n(temperature = 4–60 °C, pH = 2–12). The use of\ncost-effective ELNPs as a wood adhesive has shown a competitive shear\nstrength of ∼14.89 MPa, comparable to those of commercial bisphenol\nA epoxy resin and phenol-formaldehyde resin. The thermo-curing ELNPs\ndemonstrate excellent chemical solvent resistance and thermal stability\n(∼395 °C). Additionally, the one-step fabrication of ELNPs\ndemonstrates good scalability (≥15 kg) and commercial viability\n(472 €/ton) in wood adhesives. This one-step synthetic strategy\nprovides a promising pathway for producing high-performance and cost-efficient\nlignin-based epoxy resins that can be used as sustainable adhesives.