Structural transformation of hemicelluloses and lignin from triploid poplar during acid-pretreatment based biorefinery process

In order to understand the behaviors of hemicelluloses and lignin under the given acidic conditions with increasing severity, the structural characteristics were elucidated in detail by both wet chemistry methods and spectroscopic analyses in this study. Although acidic pretreatment significantly hydrolyzed the glycosidic linkages in xylan backbone and then reduced the molecular weight of xylan from 89,600 to 19,630 g/mol, a slightly increased amount of glucuronic acid was observed, probably attributing to the maintenance of ester bonds. The serious structural variation occurred in lignin macromolecule was evidenced by the extensive degradation of β-O-4 ether linkages and resinol substructure, together with the changes in the ratios of the three monolignols in ester-bond, ether-bond and non-condensed phenolic compounds. At the most severity, obvious condensation reactions introduced the clear shift of C2 and C5 correlations and the absence of C6 correlation in guaiacyl units by 2D HSQC analysis.