Effect of ultrasound on the physicochemical properties of organosolv lignins from wheat straw

Abstract The extractability and physicochemical properties of the wheat straw lignins were comparatively studied by using extraction methods with 0.5M NaOH in 60% aqueous methanol with and without application of ultrasonic irradiation. The results showed that applying sonication for 5, 10, 15, 20, 25, 30, and 35 min solubilized 67.4, 68.6, 74.4, 77.3, 77.3, 77.9, and 78.5% of the original lignin, whereas the treatment with 0.5M NaOH in 60% aqueous methanol at 60°C for 2.5 h without ultrasound assistance released 61.0% of the original lignin. The lignin preparations isolated by ultrasound‐assisted extractions showed slightly lower molecular weights, associated polysaccharides, and thermal stabilities during the initial stage of decomposition. More important, there were no significant differences in the primary structural features between the lignin preparations. Ultrasound‐assisted extractions under the alkaline organosolv extractions did not affect the overall structure of the lignin from wheat straw. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2512–2522, 2002