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Title
Physico-chemical characterization of different alcohol-soluble lignins from rice straw
Authors
D. SHE X. N. NIE F. XU Z. C. GENG H. T. JIA G. L. JONES and M. S. BAIRD
Received
November 21, 2011
Published
Volume 46, Issue 3-4 March-April
Keywords
rice straw, lignin, alcohol, 2D-HSQC, FT-IR, 13C NMR
Abstract
The treatment of dewaxed rice straw with 60% methanol, 60% ethanol, 60% n-propanol, 60% n-butanol, 60% ethanol containing 0.01 M HCl and 60% ethanol containing 0.25 M NaOH at 75 ºC for 3 h resulted in the solubilization of 14.6, 13.0, 16.3, 12.2, 13.0 and 75.6% of the original lignin, respectively. All alcohol-soluble lignin fractions showed spectral features of GSH-type lignin. The yield and purity of the acid-insoluble lignin extracted with 60% ethanol containing 0.25 M NaOH was much higher than of those prepared with other alcohols. The purity of lignin prepared with different alcohols followed the order: methanol > n-propanol > n-butanol > ethanol. Furthermore, the treatment of 60% ethanol under alkali catalyst produced purer lignin than the 60% ethanol treatments with or without acid catalyst. The six alcohol-soluble lignin fractions were comparatively characterized by both destructive methods, such as alkaline nitrobenzene oxidation, and non-destructive techniques, such as ultraviolet (UV), Fourier Transform Infrared (FTIR), 13C and two-dimensional Heteronuclear Single Quantum Correlation Nuclear Magnetic Resonance (13C and 2D-HSQC NMR) Spectroscopy, and Gel Permeation Chromatography (GPC). The 2D-HSQC NMR spectrum showed that the prominent linkage of the lignin fraction obtained with 60% ethanol containing 0.25 M NaOH was between the ?-O-4 ether substructure and the ?-5? and ?-?? ones.
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