PHYSICOCHEMICAL CHARACTERIZATION OF LIGNIN FRACTIONS ISOLATED FROM Dendrocalamus sinicus

Dendrocalamus sinicus, which is the largest bamboo species in the world, has broad prospects in the field of pulp and paper making as well as biorefinery. In this study, five soluble lignin fractions were sequentially isolated with 80% ethanol containing 0.025 M HCl, 80% ethanol containing 0.5% NaOH, and alkaline aqueous solutions (containing 2.0, 5.0, and 8.0% NaOH, respectively) at 75 C for 4 h from dewaxed D. sinicus materials, and their compositions and structural properties were examined. Gel permeation chromatography (GPC) and purity analysis revealed that the lignin fractions isolated by ethanol had lower weight-average molecular weights and contained much higher amounts of associated hemicelluloses, while the lignin fractions isolated by alkaline aqueous ethanol had higher weight-average molecular weights and contained lower amounts of associated hemicelluloses. Spectroscopy analyses indicated that the bamboo lignin was typical grass lignin, which consisted of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units. The major interunit linkages present in the extractable bamboo lignin are beta-O-4' aryl ether linkages, together with lower amounts of beta-beta', beta-5', and beta-1' linkages. In addition, a small percentage of the lignin side-chain was found to be acetylated at the gamma-carbon, predominantly at syringyl units. The results obtained from the research may provide basic evidences for conversion of bamboo feedstock to high value-added materials.