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Highly purified cellulose preparations were obtained by pretreatment of dewaxed barley straw, oil palm frond fiber, poplar wood, maize stems, wheat straw, rice straw, and rye straw with 2.0% H 2 O 2 at 45°C and pH 11.6 for 16 h, and sequential purification with 80% acetic acid-70% nitric acid (10/1, v/v) at 120°C for 15 min. The purified cellulose obtained was relatively free of bound hemicelluloses (2.3-3.2%) and lignin (0.4 -0.6%) and had a yield of 35.5% from barley straw, 39.6% from oil palm frond fiber, 40.8% from poplar wood, 36.0% from maize stems, 34.1% from wheat straw, 23.4% from rice straw, and 35.8% from rye straw. The weight-average molecular weights of the purified cellulose ranged from 39,030 to 48,380 g/mol. The thermal stability of the purified cellulose was higher than that of the corresponding crude cellulose. In comparison, the isolated crude and purified cellulose samples were also studied by Fourier transform IR and cross-polarization/magic-angle spinning 13 C-NMR spectroscopy.

Ten hemicellulosic preparations, obtained by treatments of the water-extracted maize stems with peroxymonosulfuric acid, peroxyformic acid, peracetic acid, and 2 % hydrogen peroxide under the conditions given, respectively, were investigated by gel permeation chromatography and spectroscopic techniques such as Fourier transform infrared and carbon-13 nuclear magnetic resonance. Under an optimum extracting condition (2 % H 2 O 2 , 45°C, 12 h, pH 11.5-12.0), the hemicelluloses obtained represented 63.3-64.7 % of the original hemicelluloses and had high weight-average molar mass between 69060 and 54740 g mol -1 . The most obvious feature was found that the alkaline peroxide treatment of the stems under the conditions used did not affect the overall structure of the hemicelluloses. The thermal stability of the hemicelluloses was found to increase slightly with increasing molar mass. All the hemicellulosic preparations were, however, to varying degree thermally unstable at temperature above 180°C. KeywordsMaize stems Hemicelluloses Hydrogen peroxide Molar mass FT-IR spectra 13 C-NMR spectrum Thermal stability 492 Brought to you by |