Effects of extraction time and different alkalis on the composition of alkali-soluble wheat straw lignins.
1996
Sun R. | Lawther J.M. | Banks W.B.
Wheat straw was extracted with 1.5% KOH at 20 degrees C for 6 h, 1.5% LiOH at 20 degrees C for 6 h, and 1.5% NaOH at 20 degrees C for 0.5, 2, 3, 4, 6, 12, 24, 48, 72, 96, and 144 h, respectively. The alkali-soluble lignin fractions were isolated by two-step precipitation, and the chemical compositions in each of the lignin fractions are reported. The physicochemical properties and structural features of these lignin fractions were characterized by GPC, UV, IR, and 13C-NMR spectroscopy and alkaline nitrobenzene oxidation. The most striking characteristics of these lignin fractions are the almost absence of neutral sugars (0.7-0.9%) and their low average molecular weights (1000-1560 Da). The results also showed that these lignin fractions contained roughly equal amounts of guaiacyl and syringyl units with relatively fewer p-hydroxyphenyl units and appeared to be very closely associated to hydroxycinnamic acids.
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