Aminated alkali lignin nanoparticles enabled formaldehyde-free biomass wood adhesive with high strength, toughness, and mildew resistance.

[Display omitted] • The conversion of industrial alkali lignin into wood adhesives was achieved. • The adhesive was green without using any aldehydes, phenols, or organic solvents. • The bonding strength and debonding work increased by 175 % and 533 %, respectively. • Water resistance and mildew resistance were significantly improved. • The adhesive was low-cost compared to commercial synthetic and biomass adhesives. The conversion of industrial lignin into wood adhesives offers a solution to issues related to formaldehyde pollution and the reliance on petrochemical resources of traditional formaldehyde-based resins, while promoting environmental and energy sustainability. However, conventional methods for preparing lignin-based adhesives generally involve the use of materials like formaldehyde, organic solvents, and costly epoxy, hindering their industrial application. This study introduces a novel approach for producing eco-friendly lignin-based wood adhesives using aminated lignin-Cu nanoparticles. The lignin-Cu nanoparticles were synthesized in water as a single solvent through a sedimentation method. Amination modification was achieved by grafting amino-terminated hyperbranched polyamide onto the nanoparticles via a Schiff base reaction. The prepared adhesive demonstrated a remarkable bonding strength of 1.51 MPa and debonding work of 0.272 J, which were 2.75 and 6.33 times higher than those of the pure lignin adhesive, respectively. Moreover, the adhesive exhibited improved water resistance with a wet shear strength of 1.15 MPa and sustained mildew resistance for approximately 100 days. Notably, this adhesive was synthesized without the use of formaldehyde, phenol, acids, or organic solvents, minimizing reliance on fossil resources and lowering costs compared to many formaldehyde-based and biomass adhesives. This research opens up new avenues for the efficient utilization of industrial lignin and the production of formaldehyde-free, environmentally friendly adhesives, which holds significant promise for energy conservation, emission reduction, and sustainable development within the wood-based panel industry. [ABSTRACT FROM AUTHOR]