A Formaldehyde-Free Lignin-Based Adhesive with High Bonding Strength, Mild Curing Conditions, and Reusability

Petroleum-based binders used in traditional wood composites are neither eco-friendly nor sustainable, highlighting the significant potential for biobased alternatives. However, traditional biobased wood adhesives often have drawbacks such as low bonding strength, low reactivity, poor water resistance, and the inability to be reused. To address these limitations, this study first prepared quinonized lignin (QSL) via a one-step oxidation method. Subsequently, a hyperbranched amino oligosiloxane nanocluster cross-linker (HAC) was synthesized by incomplete hydrolysis. The HAC enhances the adhesive’s comprehensive performance through its strong hydrophobicity, high density of reactive amino groups, and a balanced toughness–strength profile attributed to its hyperbranched structure. The resulting cured adhesive, QSLH, exhibits a high dry bond strength (≈5.30 MPa) and a wet bond strength (≈3.00 MPa) on wood. Furthermore, this lignin-based adhesive demonstrates high reactivity and reusable and mildew-resistant characteristics. The high-performance, eco-friendly, formaldehyde-free lignin-based adhesive developed in this work alleviates dependence on petrochemical resources in conventional adhesives, providing a reference for the development of biomass adhesives.