Pretreatment of kraft lignin by deep eutectic solvent and its utilization in preparation of lignin-based phenolic formaldehyde adhesive

To improve the reactive sites of kraft technical lignin, a deep eutectic solvent (DES) composed ZnCl2 / lactic acid was used to pretreat lignin from coniferous wood. The modified and unmodified were replace different proportions phenol (50%, 60%, 70%) prepare lignin-phenol-formaldehyde (LPF) adhesive. phenolic hydroxyl content DES-treated increased 3.12 wt% 3.93 methoxy decreased 11.83 6.64 under optimized experimental conditions. bond strength LPF adhesive prepared by DES reagent activated higher than that control sample. When substitution degree for reached 70%, plywood DES-pretreated 0.79 MPa free formaldehyde 0.28%, which met requirements Chinese national standard GB/T 9846 (2015). However, viscosity sample, results indicate modification cannot resin.