Fractionation and characterization of lignin carbohydrate complexes (LCCs) of Eucalyptus globulus in residues left after MWL isolation. Part I: Analyses of hemicellulose-lignin fraction (HC-L)

The residual wood meal left after milled wood lignin (MWL) isolation (MWR) was extracted with the cellulose solvent lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) to obtain a soluble fraction (C-L) and an insoluble fraction (C-L-residue). The C-L-residue was further extracted with the hemicellulose solvent 3 M NaOH to give a soluble fraction named hemicellulose-lignin fraction (HC-L) with 21.3% yield based on MWR. It was found that HC-L was composed of xylan, cellulose and lignin with abundant S-type β-O-4 substructures. HC-L lignin was bonded to HC-L cellulose or HC-L hemicelluloses or both. The method, which comprised acetylation for hardwood xylan (by acetic anhydride/pyridine/formamide) and extraction with chloroform, was found to be effective for selective xylan acetate fractionation. HC-L was further fractionated by the same method and subsequent deacetylation to give a xylan-lignin fraction (X-L) in 11.3% yield based on HC-L. X-L was composed mainly of xylan and lignin with abundant S-type β-O-4 substructures, and bonded to X-L xylan. X-L is considered as a promising fraction for elucidation of the structure of lignin-carbohydrate linkages.