Physicochemical and Thermal Characterization of Wheat Straw Hemicelluloses and Cellulose

Abstract

Dewaxed wheat straw was treated with 3% NaOH at 45 °C for 2, 5, 12, or 15 h, on a large scale with a low extractant/sample ratio. The treatments resulted in the release of 32.7−41.5% hemicellulose−lignin complexes, which contained 9.3−14.2% associated lignins. The residues of the treated straw were sequentially delignified with NaClO2 and then extracted with 10% KOH at 25 °C for 16 h. The yields of residual hemicelluloses and cellulose ranged between 4.5−9.8 and 38.0−39.9%, respectively. Xylose was the major sugar constituent in all of the complexes and residual hemicellulosic fractions, whereas arabinose, glucose, and galactose were present as minor components. The major phenolic units released by nitrobenzene oxidation products from the associated lignins were vanillin and syringaldehyde in all of the complexes and residual hemicellulosic fractions. The isolated complexes and hemicelluloses were also characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis, and the results are reported. Keywords: Hemicellulose−lignin complexes; sugars; lignin; uronic acids; phenolic acids and aldehydes; molecular weight