High-Performance Formaldehyde-Free Lignin Adhesives from Sugarcane Bagasse via Epoxy Cross-Linking

Abstract Lignin derived from sugarcane bagasse presents a sustainable and completely formaldehyde-free alternative to conventional wood adhesives. In this study, a water-based epoxy modification strategy was developed to construct a three-dimensional cross-linked network, supported by a two-stage orthogonal design to optimize reaction parameters. The resulting adhesive achieved a bonding strength of 2.72 ± 0.15 MPa—3.9 times higher than the national standard—while the activation energy for thermal decomposition increased by 64.5 percent (162.4 ± 5.6 kJ/mol). Scanning electron microscopy revealed a dense, compact morphology in heat-dried films, correlating with >90 percent wood failure rates (within the wood substrate itself, rather than at the adhesive–wood interface), whereas freeze-dried samples exhibited a porous network structure with reduced cohesion. X-ray diffraction and thermogravimetric/derivative thermogravimetric analyses confirmed the thermal–mechanical reinforcement effect of epoxy cross-linking, with the optimized adhesive maintaining 78.5 percent mass retention after 72 hours of aging at 300°C. Importantly, the adhesive was synthesized entirely from formaldehyde-free raw materials, and the trace-level formaldehyde emissions of particleboards (0.02 mg/liter) are attributed to the natural background of wood rather than the adhesive itself, fully complying with Enropean Norm Formaldehyde（ENF）standards. This work offers a scalable route to transform agricultural waste into high-performance, formaldehyde-free wood adhesives, delivering both environmental and industrial benefits.