Structural characterization of soluble lignin in the pre-hydrolysis liquor of bamboo-willow dissolving pulp

The soluble lignin present in the pre-hydrolysis liquor (PHL) is detrimental for value-added utilization of the PHL from production of kraft-based dissolving pulp. In this paper, the soluble lignin was separated from PHL by activated carbon adsorption and subsequent desorption with methanol. The structural characteristics of the soluble and dioxane lignins (from bamboo-willow material) were analyzed by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). The FTIR and proton-NMR results showed that cleavage of β-O-4 aryl-ether linkages and demethylation occurred in the lignin structure during the pre-hydrolysis. The main linkages between structural monomeric units of the soluble lignin were β-β, β-5, β-1, and β-O-4. Additionally, the TGA results showed that the residual char yield at 800 °C of the soluble and dioxane lignins were 33.4% and 35.3%, respectively. Therefore, the soluble lignin obtained from PHL possessed thermal stability comparable to that of dioxane lignin, and can be used as a renewable source for carbon fiber.

Investigation of structure of milled wood and dioxane lignins of Populus nigra and Cupressus sempervirens using the DFRC method

In this study, derivatisation followed by reductive cleavage (DFRC) were used to investigate milled wood lignin (MWL) and dioxane lignin (DL) structures of Populus nigra and Cupressus sempervirens. After the DFRC reactions, the constituents obtained from these two kinds of lignin were recognised structurally using several chromatographic and spectral methods such as 13C NMR, GC-MS, and GPC. Comparative results showed that the dominant structural components of the two kinds of lignin are obtained from the cleavage of β-O-4 bonds. The main component of DL and MWL of P. nigra is 4-hydroxy-3,5-dimethoxy-1-phenyl-γ-hydroxypropene (syringyl structures). Also, some guaiacyl structures were observed. The dominant component identified in both lignins of C. sempervirens is 4-hydroxy-3-methoxy-1-phenyl-γ-hydroxypropene (guaiacyl structures). The cleavage method has a good performance for both P. nigra and C. sempervirens and the results obtained are in good agreement with previously published data.

Isolation and Characterization of Lignin from Tropical and Temperate Hardwood

Dioxane and milled wood lignins (MWL) were isolated from tropical hardwood, Nalita (Trema orientalis) and temperate hardwood, aspen. These lignins were characterized by UV, FTIR, 1H-NMR and 13C-NMR spectroscopy, alkaline nitrobenzene oxidation, molecular weight determination, elemental and methoxyl analysis. The structural analysis revealed that Nalita and aspen lignin is syringyl-guaiacyl type. Aspen lignin had higher syringyl unit than Nalita lignin. The β-O-4 type linkages are the main interunit linkages and more abundant in aspen than Nalita. Dioxane lignin showed higher free phenolic hydroxyl group than MWL in both species. The weight average molecular weight of aspen lignin was lower than that of Nalita lignin. Nalita and aspen lignins contained both erythro and threo configuration, but erythro proton gave stronger peak. A UV absorption maximum of aspen lignin was at 274 nm, whereas it was shifted to 280 nm for Nalita lignin. Keywords: Trema orientalis, Aspen, Dioxane lignin, Milled wood lignin, Syringyl-guaiacyl, β-O-4 linkages DOI: 10.3329/bjsir.v44i3.4399 Bangladesh J. Sci. Ind. Res. 44(3), 271-280, 2009