The effect of ionic liquids pretreatment on the distribution and structure of alkali-soluble hemicelluloses from Eucalyptus

In this study, Eucalyptus was treated by an integrated process based on ionic liquids ([Bmim]Cl and [Bmim]OAc) combined with successive alkali solutions (0.5, 2.0, and 4.0% NaOH). The dynamic distribution changes of hemicelluloses on the morphologically distinct regions in the treated Eucalyptus cell walls revealed that the dissolution of hemicelluloses mainly occurred in the secondary layers during this process. In addition, the structural features of alkali-soluble hemicelluloses dissolved from ionic liquids pretreated Eucalyptus were thoroughly investigated. The [Bmim]OAc pretreatment promoted the separation of hemicelluloses with relatively high molecular weights in the following alkali extractions, accompanying with slightly structural changes. The alkali-soluble hemicelluloses obtained from Eucalyptus are characterized to be a linear backbone of (1 → 4)-linked-β-D-xylopyranosyl residues decorated with branch at O-2 of 4-O-methyl-α-glucuronic acid unit. Additionally, the thermal stability of hemicelluloses was also increased by the ionic liquids pretreatment.