Physicochemical characterization of lignin fractions sequentially isolated from bamboo ( Dendrocalamus brandisii ) with hot water and alkaline ethanol solution

Nine lignin fractions from bamboo ( Dendrocalamus brandisii ) were sequentially isolated with hot water at 80, 100, and 120°C for 3 h and 60% aqueous ethanol containing 0.25, 0.5, 1.0, 2.0, 3.0, and 5.0% NaOH at 80°C for 3 h. Molecular weight and purity analysis revealed that the lignin fractions isolated by hot water (L 1 , L 2 , and L 3 ) had lower weight‐average molecular weights (between 1350 and 1490 g mol −1 ) and contained much higher amounts of associated hemicelluloses (between 9.26 and 22.29%), while the lignin fractions isolated by alkaline aqueous ethanol (L 4 , L 5 , L 6 , L 7 , L 8 , and L 9 ) had higher weight‐average molecular weights (between 2830 and 3170 g mol −1 ) and contained lower amounts of associated hemicelluloses (between 0.63 and 1.66%). Spectroscopy (UV, FTIR, 13 C‐NMR, and HSQC) analysis showed that the bamboo ( Dendrocalamus brandisii ) lignin was typical grass lignin, consisting of p ‐hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units. The major interunit linkages presented in the alkaline aqueous ethanol extractable bamboo lignin were β‐O‐4′ aryl ether linkages (about 74.3%), followed by β‐β′ resinol‐type linkages and β‐1′ spirodienone‐type linkages (both for 7.8%), together with small amounts of β‐5′ phenylcoumaran (6.8%) and p ‐hydroxycinnamyl alcohols end groups (3.1%). In addition, a small percentage (1.0%) of the lignin side‐chain was found to be acetylated at the γ‐carbon, predominantly over syringyl units. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012