Formaldehyde-free biomass adhesive based on industrial alkali lignin with high strength and toughness

The preparation of industrial lignin-based adhesives generally requires the use of large amounts of petrochemical products or toxic and hazardous reagents, which severely limits their widespread application in the wood-based panel industry. In this study, we present a novel approach for synthesizing an eco-friendly lignin-based wood adhesive using aminated alkali lignin (AAL) and epoxy-terminated hyperbranched polyester (EHBP). The AAL was prepared by aminating alkali lignin through a green and formaldehyde-free method. The EHBP was synthesized by grafting epichlorohydrin onto biomass-derived hyperbranched polyester. The resulting adhesive performed excellent bonding strength of 2.41 MPa and debonding work of 0.711 J, which were 3.63 and 15.2 times higher than those of the pure lignin adhesive, respectively. This exceptional bonding strength surpassed that of most previously reported biomass adhesives. The moisture uptake value of the adhesive decreased by 75.6 % and the residual rate increased by 239.2 %. In addition, the prepared adhesive exhibited enhanced mold resistance. Importantly, the adhesive was primarily composed of biomass materials and their derivatives and was less costly than most commercial formaldehyde-based and bio-based adhesives. This work presents new possibilities for the high-value utilization of industrial lignin and the development of formaldehyde-free and environmentally friendly adhesives.