jf034633j_si_001.pdf (38.62 kB)
Inhomogeneities in the Chemical Structure of Sugarcane Bagasse Lignin
journal contribution
posted on 2003-11-05, 00:00 authored by Jing-Xia Sun, Xaio-Feng Sun, Run-Cang Sun, Paul Fowler, Mark S. BairdSequential treatments of dewaxed bagasse with distilled water, 0.5 M NaOH, 0.5, 1.0, 1.5, 2.0, and
3.0% H2O2 at pH 11.5, and 2 M NaOH at 55 °C for 2 h solubilized 2.8, 52.5, 14.9, 3.3, 5.5, 5.0, 2.8,
and 2.2% of the original lignin, respectively. The eight isolated lignin fractions were subjected to a
comprehensive structural characterization by UV, FT-IR, and 1H and 13C NMR spectroscopies and
thermal analysis. The nitrobenzene oxidation method was also applied to the in situ lignins. The
seven lignin fractions, isolated successively with alkali and alkaline peroxide, were all SGH-type lignins,
with a small amount of esterified p-coumaric acid and mainly etherified ferulic acid. No significant
differences were found in the weight-average molecular weights (1680−2220 g/mol) of the seven
alkali and alkaline peroxide dissolved lignins. However, the first four lignin fractions, isolated with 0.5
M NaOH and 0.5, 1.0, and 1.5% H2O2 at pH 11.5, were rich in syringyl units and contained large
amounts of noncondensed ether structures, whereas the last three lignin fractions, isolated sequentially
with 2.0 and 3.0% H2O2 at pH 11.5 and 2 M NaOH at 55 °C for 2 h, had a higher degree on
condensation and were rich in guaiacyl lignins.
Keywords: Bagasse lignins; sugars; molecular weight; UV; FT-IR; 1H and 13C NMR; nitrobenzene
oxidation; phenolic acids