Formaldehyde-Free, High-Bonding Performance, Fully Lignin-Based Adhesive Cross-Linked by Glutaraldehyde

The traditional phenolic resin is prepared by the reaction of petroleum-based phenol and carcinogenic formaldehyde, which causes serious harm. As a renewable phenolic compound with abundant reserves in nature, lignin as a potential sustainable substitute for phenol-formaldehyde resin and lignin-phenol-formaldehyde resin adhesives have attracted increasing attention for the production of plywood. However, how to exploit environmentally friendly fully lignin-based adhesives remains a challenge. Here, formaldehyde-free fully lignin-based adhesive was synthesized using a facile strategy by cross-linking lignin using glutaraldehyde. The structural characterization confirmed that lignin successfully reacted with aldehydes and promoted the nucleophilic addition reaction during the synthesis of glutaraldehyde cross-linked fully lignin-based adhesives. The plywood prepared with the glutaraldehyde cross-linked fully lignin-based adhesive exhibited excellent adhesion performance, and the dry and bonding strength reached 2.66 and 0.93 MPa, respectively, indicating comparable competitiveness compared with the traditional phenolic resin adhesive and lignin-based formaldehyde adhesive. The work demonstrates a facile strategy to synthesize formaldehyde-free fully lignin-based adhesive that enables its utilization as promising alternatives to traditional adhesives.