Fractional extraction and structural characterization of sugarcane bagasse hemicelluloses

Over 90% of the original hemicelluloses in the cell walls of bagasse were sequentially extracted with distilled water, 0.5 M NaOH, 0.5, 1.0, 1.5, 2.0 and 3.0% H2O2 at pH 11.5, and 2.0 M NaOH at 55 degreesC for 2 h. Meanwhile, the successive treatments also released 89.0% of the original lignin. Chemical composition, physico-chemical properties, and structures of the eight hemicelluloses were elucidated by a combination of sugar analysis, nitrobenzene oxidation of bound lignin, molecular determination, Fourier transform infrared, and H-1 and C-13 NMR spectroscopy and thermal analysis and the results are reported. The results showed that the sequential treatments were very effective on the fractionation of hemicelluloses from bagasse, and the extraction strength, such as alkali and H2O2 concentration, had a great influence on the chemical and structural features of the hemicelluloses, e.g. content of associated lignin and molecular weight. The hemicellulosic fraction, isolated with 0.5% H2O2 at pH 11.5 for 2 h under 55 degreesC, had a backbone of xylose residues with beta-(1 --> 4) linkages and were branched mainly through arabinofuranosyl and 4-O-methyl glucopyranosyl units. Ferulic and p-coumaric acids were found to be esterified to the hemicelluloses. (C) 2004 Elsevier Ltd. All rights reserved.