Reactivity improvement by phenolation of wheat straw lignin isolated from a biorefinery process

Abstract

Phenolation can effectively improve the reactivity of lignin by directly increasing the phenolic hydroxyl groups and reactive sites for adhesive applications. Wheat straw residue isolated from an autohydrolysis/refining/enzymatic hydrolysis process was phenolated to improve the reactivity of lignin. The optimum phenolation conditions were determined to be a lignin/phenol (L/P) ratio of 1/3 with a 10% acid charge at 120 °C for 2 hours. Phenolated lignin resulted in 32 wt% of phenol incorporated onto lignin and a significant decrease in molecular weight. A comprehensive characterization indicated that all lignin substructures (β-O-4′, β-5′/α-O-4′, β-β′, ferulate, p-coumarate and p-benzoate) were reacted along with a hydrolysis of over 50% of polysaccharides during phenolation, resulting in a decrease in aliphatic hydroxyl groups and an increase in the phenolic hydroxyl groups. Phenol was incorporated onto both the sidechains and aromatic nuclei. These improvements in lignin reactivity will enable it to be used in adhesives with higher substitution rates.