Sustainable fabrication of fully bio-based wood adhesives via brown-rot fungi depolymerized lignin: a circular approach for agricultural residues.

Wood-based panels are extensively utilized in construction, furniture and various interior decoration products. However, over 90% of the adhesives employed in their fabrication are formaldehyde-based, relying not only on non-renewable petroleum resources but also releasing hazardous formaldehyde during use, posing significant risks to environmental safety and human health. This study presented a No-Added-Formaldehyde, fully bio-based adhesive system, fabricated by extracting highly reactive lignin from brown-rotted wood and formulating it into an aqueous suspension. This adhesive was applied to eucalyptus veneers to prepare panels. The optimized hot-pressing parameters (160 °C, 8 min) yielded a robust dry bonding strength of 1.23 MPa. Fluorescence microscopy characterization of the bonding interphase revealed maximum effective and absolute penetration depths. Furthermore, three-dimensional visualization via X-ray computed tomography (X-CT) confirmed the formation of mechanical interlocking structures, adhesive forms a "glue-nail" structure at the bonding interface. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) demonstrated that the hot-pressing process induced concurrent lignin depolymerization and condensation reactions, leading to the formation of a stable cross-linked network rich in CC bonds. This work provided a promising and sustainable strategy for developing high-performance, eco-friendly wood adhesives.