Structural Characterization of Bamboo Lignin Isolated With Formic Acid and Alkaline Peroxide by Gel Permeation Chromatography and Pyrolysis Gas Chromatography Mass Spectrometry

Abstract

Fractionation is an effective technology to maximize the utilization of lignocelluloses for the production of chemicals and materials. In this case, bamboo was subjected to a two-step fractionation process based on the concept of biorefinery: (a) formic acid treatment at boiling point under atmospheric pressure for 2 h, and (b) posttreatment with alkaline hydrogen peroxide solution containing 1% NaOH and 1% H2O2 at 80 oC. The combination of formic acid delignification and alkaline hydrogen peroxide degradation achieved an effective removal of both lignin (delignification rate 94.9%) and hemicelluloses (removal rate 87.4%) from bamboo, producing celluloserich pulp, formic acid lignin and sugars. To investigate the structural modification of lignin during the fractionation process, the residual lignin in the treated samples was isolated and characterized with multiply techniques including gel permeation chromatography, pyrolysis gas chromatography mass spectrometry, Fourier-transform infrared spectroscopy, etc. The relative ratio of S/G was 1.63 for bamboo milled wood lignin (L1), whereas the lignin isolated from the formic acid treated cellulose-rich fraction (L2) presented a chromatograph similar to that of L1 but had a lower S/G ratio of 1.28. This indicated that a preferential removal of S units during the formic acid fractionation process. In addition, alkaline hydrogen peroxide treatment resulted in more removal of S units, as indicated by a lower S/G ratio of 0.71.