PHYSICOCHEMICAL AND THERMAL CHARACTERIZATION OF WHEAT-STRAW HEMICELLULOSES AND CELLULOSE

Dewaxed wheat straw was treated with 3% NaOH at 45 degrees 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 th en extracted with 10% KOH at 25 degrees C for 16 h. The yields of resi dual 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, gl ucose, and galactose were present as minor components. The major pheno lic units released by nitrobenzene oxidation products from the associa ted lignins were vanillin and syringaldehyde in all of the complexes a nd residual hemicellulosic fractions. The isolated complexes and hemic elluloses were also characterized by Fourier transform infrared spectr oscopy and thermogravimetric analysis, and the results are reported.