Abstract
Four alkali-soluble lignin fractions were extracted from dewaxed wheat straw with 3% sodium hydroxide at 45°C for 2, 5, 12, and 15 h, respectively. The pure alkali-soluble lignin preparations LA were obtained by using a two step precipitation method instead of the traditional ether precipitation procedure. The physico-chemical properties and structural features of the isolated pure lignin fractions were characterized by UV, FT-IR, 13C NMR spectroscopy, and thermal analysis. The lignin in fraction LA-1 is mainly composed of β-O-4 ether bonds. The less common β-5 and β-β carbon-carbon linkages are also present in the lignin structural units. The results obtained showed that the lignin fractions appeared to be strongly associated to hydroxycinnamic acids such as p-coumaric and ferulic acids and glucuronic acid or 4-O-methylglucuronic acid.
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