Mussel-inspired robust and waterproof soybean protein adhesives enhanced with phenolated lignosulfonate for wood bonding.

Plant protein-based adhesives are favored for their cost-effectiveness and environmental friendliness. However, the low reactivity of plant protein and inherent water sensitivity of its adhesive significantly limits their scalability and broader application. Drawing inspiration from mussels, we developed a robust and waterproof bio-based adhesive reinforcing soybean protein (SP) with lignosulfonate. Specifically, the lignosulfonate was modified with phenol and epoxidated to synthesize phenolated lignin epoxy resin (PLEP), which was then added into SP matrix. The resulting adhesive demonstrated excellent bonding performance, with a dry shear strength of 3.59 MPa and a wet shear strength of 2.07 MPa. Finite Element Method (FEM) simulation confirmed a decreased stress concentration due to energy dissipation for the SP/PLEP. Furthermore, the adhesive exhibited an 81.22 % residual rate after water immersion. The adhesion strength was enhanced due to the π-π/cation-π interactions, hydrogen bonds, metal coordination of calcium ions, and covalent bonds formed by amino groups in proteins. Molecular dynamics (MD) analysis verified the enhancement of intermolecular interaction after phenolic modification. Life cycle assessment (LCA) revealed that the environmental impact of SP/PLEP adhesive was lower than that of urea-formaldehyde resin. This study presents a soybean-based adhesive inspired by mussel, offering a straightforward strategy for developing biomimetic adhesives.