Structural characterization of poplar lignin based on the microwave-assisted hydrothermal pretreatment.

Abstract Increasing application for lignin due to its unique aromatic structures has encouraged the development of pretreatment techniques for lignin separation and recovery. In this work, the integration of microwave-assisted hydrothermal pretreatment (MW-HTP) and alkaline post-treatment was proposed for separating lignin from poplar wood and revealing its structural characteristics. Results showed that the yields of the lignins fractionated via the integrated treatment based on MW-HTP were increased up to 52.6%, and their associated sugars contents were clearly decreased to 0.19–0.09%, as compared to the fractionated lignins without the microwave pretreatment (29.8% and 0.29%). Interestingly, the integrated treatment based on MW-HTP promoted the cracking of β-O-4 ethers in the lignin macromolecules of poplar wood, resulting in the raise of their phenol OH groups up to 2.36 mmol/g. Overall, the fulfillment of this work will be conducive to improve the fractionation and efficient utilization of lignin in biorefinery industry.