Comparative characterization of ethanol organosolv lignin polymer from bamboo green, timber and yellow

In order to make better use of bamboo resources in industrial processes, it is necessary to understand its recalcitrant morphological stem structure and unique chemical composition. In the present work, microspectroscopic imaging approaches were used to reveal the heterogeneous distribution of lignin at cellular and subcellular level. Results showed the higher lignin concentration in the narrow layer of fiber and parenchyma secondary cell walls. Furthermore, ethanol organosolv lignin, isolated from different zones of the bamboo vascular tissue [outer (green), middle (timber) and inner (yellow)], was subjected to extensive structural characterization, including chemical component analysis, Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric/differential thermal analysis (TGA/DTA), and nuclear magnetic resonance (NMR). Main chemical differences among the green, timber and yellow zone were sugar content and S/G/H ratios. Since bamboo green had higher density, hardness and lignin content than bamboo timber and bamboo yellow, the mass transfer during the organosolv process was limited and resulted in the reduced removal/dissolution of polysaccharides at the same acidic conditions. Because bamboo green exhibited the highest content of G units in the vascular tissue, it was more condensed and thus had increased thermal stability compared to bamboo timber and bamboo yellow.