A Mortise-Tenon Inspired, Recyclable Lignin-Based Vitrimer Solid Adhesive Achieving High-Performance and Multifunctional Integration via a Covalent Adaptable Network

Conventional adhesives typically rely on toxic reagents such as phenol and formaldehyde, forming irreversible covalent networks upon curing. In this study, highly reactive uncondensed lignin was prepared using a green solvent, followed by epoxidation to facilitate its nanoscale formation. Subsequently, the lignin was copolymerized with dithiol borate, polyethylene glycol was incorporated to modulate the flexibility of the covalent adaptable network, thereby constructing a lignin-based vitrimer solid adhesive (LVSA). In particular, the dry and wet bonding strengths of VD3H3 adhesive to bamboo strips reached 19.16 and 11.70 MPa, respectively. This LVSA features thermal processability, recyclability, and photothermal conversion performance. Moreover, the functional chain segments facilitate the lignin adhesive to exert a gas-phase-solid-phase flame-retardant mechanism, with a limiting oxygen index (LOI) of 43.8%. This work presents an design strategy for the development of high-strength, recyclable, and multifunctional green LVSA, paving the way toward a approach for the high-value utilization of lignin.