Physico-chemical and structural characterization of residual lignins isolated with TAED activated peroxide from ultrasound irradiated and alkali pre-treated wheat straw

Post-treatment of ultrasonic irradiated and alkali pre-treated wheat straw with TAED activated peroxide at pH 11.8 for 12 h at 48 °C resulted in a dissolution of 43.3–46.2% of the original lignin and 27.1–28.1% of the original hemicelluloses, respectively. The isolated acid-insoluble lignin preparations were analysed by both destructive methods such as alkaline nitrobenzene oxidation and non-destructive techniques such as UV, FT-IR, and 13C NMR spectroscopy as well as GPC. Total polysaccharide content of isolated lignin preparations ranged from 0.79 to 1.01%. Nitrobenzene oxidation analysis showed that the molar ratio of V:S:H in the eight lignin preparations was 6:5:1. In addition, the residual lignins isolated by TAED activated peroxide showed a higher molecular weight and thermal stability than the lignins released during the pre-treatment with alkali combining with or without ultrasonic assistance. Furthermore, it was found that more hydroxyl, aldehyde and ketone groups and aryl ethers in the lignin side chains were attacked with the use of TAED. [Copyright &y& Elsevier]