Transformation of lignin from bioethanol production for phenol substitution in resins

The main objective of biorefineries is the efficient conversion of lignocellulosic materials into valuable products. Lignin, a major abundant polymer not sufficiently exploited, is considered to be a promising substitute of phenol in phenol–formaldehyde resin synthesis. In this study, a lignin sample from a bioethanol production plant was modified under different experimental conditions by a depolymerisation treatment. The modification was intended to enhance the reactivity of lignin by increasing its functionality. The structural changes were studied with several characterisation techniques including size exclusion chromatography, Fourier transform infrared spectroscopy and nuclear magnetic resonance. The lignin reactivity towards formaldehyde was determined with a formaldehyde reactivity test. From the characterisation results of the reacted lignins, it was concluded that increasing the severity of the depolymerisation treatment (i.e. higher temperature, reaction time and catalyst content) resulted in an increase in active functional groups. Consequently, lignins depolymerised at more severe conditions were more reactive towards formaldehyde reaction. Due to their improved reactivity, the treated lignins could be successfully used as substitutes of phenol, converting them into a highly value-added product. An estimation of the cost of the proposed process is provided.