Preparation of Lignin-Phenol-Formaldehyde Resin Adhesive Based on Active Sites of Technical Lignin

In this study, a novel method was applied to calculate the active sites of technical lignin for the preparation of lignin-phenol-formaldehyde resin adhesive based on quantitative P-31 NMR analysis of the technical lignin. Lignin-phenol-formaldehyde resin adhesives with 10%-60% substitution rates and low residual toxicity were successfully synthesized. The bonding strength (0.84-1.35 MPa) and formaldehyde emission (0.11-0.24 mg/L) of poplar plywood bonded by the prepared resin adhesives meet the requirements of the first grade (>= 0.7 MPa) and the E-0 grade (<= 0.5 mg/L) of plywood, based on the Chinese National Standard (GB/T 17657-2013). These results indicate that the lignin-phenol-formaldehyde resin adhesives synthesized using the designed formulation could effectively control formaldehyde emissions while not significantly depleting the bonding strength of the bonded plywood. In addition, FT-IR and NMR analysis confirmed that the prepared lignin-phenol-formaldehyde resin adhesives based on the designed formulation have a chemical structure and curing behavior that is similar to that of the control phenol formaldehyde resin adhesive.