Characterization of hemicelluloses obtained by classical and ultrasonically assisted extractions from wheat straw

The extractability of the wheat straw hemicelluloses was investigated using extraction method with and without application of ultrasonic irradiation in 0.5 M KOH aqueous solution. The isolated eight hemicellulosic preparations were comparatively characterised by yield, composition, structural and molecular properties, and thermal stability. The results showed that ultrasonically assisted extraction in a period of 20-35 min produced a slightly higher yield of hemicelluloses and lignin than those of the classical alkali procedure by 0.8-1.8% of the original hemicelluloses and 0.6-5.3% of the original lignin, respectively. The hemicelluloses, obtained by ultrasound-assisted extraction, seemed more linear and less acidic than that of the hemicelluloses extracted by alkali in the absence of ultrasonic irradiation. In addition, the hemicellulosic preparations obtained by ultrasound-assisted extractions showed a relatively lower content of associated lignin, but a higher molecular weight and a slightly higher thermal stability in comparison with the hemicelluloses isolated by alkali without ultrasonic irradiation. However, there were no significant differences between the primary structural features of the hemicellulosic preparations obtained by extraction in 0.5 M KOH solution with and without application of ultrasound. (C) 2002 Elsevier Science Ltd. All rights reserved.