Physico-chemical and thermal characterization of cellulose from barley straw

Sequential treatments of dewaxed barley straw with 1.5% H2O2 at pH 12.0 for 14 h at 40 °C under various ratios of straw to extractant and with 80% acetic acid-70% nitric acid (10/1, v/v) at 120 °C for 15 min yielded the purified cellulose ranging between 35.4 and 36.4%, which were relatively free of bound hemicelluloses (2.1-3.2%) and lignin (0.5-0.7%) and had a molecular weight ranging from 50,810 to 56,620 g/mol. In comparison, the crude cellulose, obtained by pre-treatment with 1.5% H2O2 at pH 12.0 for 14 h at 45 °C under the straw to extractant ratio of 1:18, was further, respectively, treated with xylanase at 35 °C for 42 h and 10% NaOH at 25 °C for 6 h. The yield of the two corresponding purified cellulose samples was 38.2 (F8b) and 39.3% (F9b), which contained 3.9 and 4.6% non-cellulose sugars and in 1.8 and 2.7% lignin, respectively. Both crude cellulosic samples and purified cellulosic preparations were further characterized by FT-IR and CP/MAS 13C NMR spectroscopy. The cellulose crystallinity was found to be higher in the purified cellulose than in the crude cellulose. The thermal stability of the purified cellulose was higher than that of the corresponding crude cellulose.