Lignin-based waterborne polyurethane for sustainable wood adhesives with enhanced strength and anti-aging properties

Conventional wood adhesives relying on petroleum-derived raw materials pose sustainability challenges. Here, the biomass of lignin is utilized to synthesize waterborne polyurethane (LWPU), partially reducing the usage of petroleum-based polyols while achieving robust wood adhesion. The dual crosslinking architecture, including lignin-incorporated covalent networks and hydrogen bonding, endows the LWPU elastomers with high toughness, an optimal tensile strength of 37.1 MPa, and excellent adhesion with an optimal lap shear strength of 12.7 MPa. In addition, the dynamic phenol-carbamate and hydrogen bonds render the LWPU reprocessable by hot-pressing, maintaining a lap shear strength of 4.1 MPa after three reattachment cycles. Moreover, the incorporation of lignin enhances the resistance to thermo-oxidative aging and improves the degradation rate in an alkaline ethanol solution. Particle and laminated wood boards prepared with LWPU exhibit flexural strengths of 15.2 and 42.0 MPa, demonstrating the great potential of LWPU as a wood adhesive. This work presents a reliable strategy for utilizing lignin to develop sustainable and high-performance WPU wood adhesives.