Lignin–phenol–formaldehyde resin adhesives prepared with biorefinery technical lignins

In this study, four biorefinery technical lignins were used to synthesize lignin–phenol–formaldehyde (LPF) resin adhesives with a proposed formulation that was designed based on accurate analysis of the active sites in lignin with 31 P nuclear magnetic resonance (NMR). The properties of the LPF resin adhesives and the plywoods prepared with them were tested. The structural features and curing behavior of the LPF resin adhesives were thoroughly investigated by solution‐ and solid‐state 13 C NMR. Results indicated that the proposed formulation exhibited favorable adaptability for all four of these technical lignins for synthesis of LPF resin adhesives. High‐performance plywood with low emissions of formaldehyde could be successfully prepared with the synthesized LPF resin adhesives. All the LPF resin adhesives exhibited similar structure and curing behavior with the commercial phenol–formaldehyde (CPF) resin adhesive. However, the LPF resin adhesives showed relatively higher curing temperatures as compared with the CPF resin adhesive.