Replacing Phenol and Formaldehyde for Green Adhesive Synthesis by Lignin and Furfural

Traditional phenol-formaldehyde resin involves the use of petrochemical-based phenol and formaldehyde as feedstocks, raising environmental and health concerns. Herein, renewable biobased substances, i.e., lignin and furfural, were employed to partially replace petroleum-based phenol and formaldehyde for developing greener adhesives by batch copolymerization method. The substitution rates of phenol by acetonitrile-extracted lignin and formaldehyde by furfural can reach 80 and 15%, respectively. The application of these greener raw materials can effectively decrease the emission of toxic content, increasing the viscosity and thermal stability without any sacrifice in the binding performance. The resin with 40% phenol substitution rate and 15% formaldehyde substitution rate displayed superior trade-off between bonding strength (a wet tensile strength of 1.68 MPa) and free formaldehyde content (0.21%) among all biobased resins, much superior to those of commercial adhesive (0.7 MPa and 5%) and those prepared with industrial lignin (0.66 MPa and 0.38%). By using two major biomass-derived feedstocks, this work provides a sustainable strategy to develop a green adhesive featuring superior adhesive properties, enhanced environmental compatibility, and improved thermal stability that shows a broader application potential in the adhesive field.