Preparation and evaluation of lignin-phenol-formaldehyde resin as wood adhesive using unmodified lignin

Lignin acted as phenolic polymer is a sustainable substitute for phenol to synthesize lignin-phenol-formaldehyde (LPF). Here, PLPF resins were prepared with unmodified PHP-lignin derived from phosphoric acid plus hydrogen peroxide (PHP) pretreatment of biomass waste, the PHP-lignin has plentiful hydroxyl structure and is beneficial to the polymerization with formaldehyde. Meanwhile, ALPF resin synthesized with alkali lignin abundantly produced from pulp and paper industry was also included. The feasibility of lignin as a substitute for phenol, the application of the synthesized PLPF resin in particleboard production and the obstacle on the high-value utilization of waste lignocellulosic biomass due to the existence of the resin adhesive were evaluated. Results indicated that the resins were successfully synthesized when phenol was substituted by 25% lignin. The basic properties, including solid content, free phenol content, free formaldehyde content, viscosity and adhesion performance all met Chinese National Standard (GB/T 14732–2006) of phenol-formaldehyde (PF) resin. The shaped particleboard with PLPF resin usage ranged from 5% to 15% all had good dimensional stability and solvent resistance. Finally, we verified the resin adhesive in the particleboard would greatly influence its enzymatic hydrolysis performance. The cellulose-glucose conversion of hydrothermal pretreated particleboard was merely 18.3%. Detoxification was the first and most important step in the subsequent high-value utilization of waste particleboard, and alkali pretreatment suggested a possible way to eliminate the negative effects, which could improve cellulose-glucose conversion to 57.8%.