Phenol-Enhanced Depolymerization and Activation of Kraft Lignin in Alkaline Medium

Phenolation is an effective method to improve the reactivity of lignin in the synthesis of lignin–phenol–formaldehyde (LFP) resin. Previous lignin phenolation was almost exclusively catalyzed by acid. This study investigated the phenolation of kraft lignin (KL) in alkaline medium under different conditions of the mass ratio of phenol to lignin, reaction temperature, and reaction time. Results indicated that under the conditions of a mass ratio of phenol to KL of 3:1, a temperature of 160 °C, and time of 2 h, KL was depolymerized to phenolated lignin segments (51.2%), monomeric and dimeric phenolics (12.5%), and organic acids (36.3%). The lignin segments had low molecular weight, narrow dispersity, and high phenolic hydroxyl group (4.5 mmol/g), which could be used as precursors of LFP resin/adhesive. The phenolics and organic acids would have a potential as platform chemicals.