| In this doctoral dissertation, lignin, hemicelluloses, and lignin-hemicelluloses complex (LCC) were isolated from Dendrocalamus brandisii and Dendrocalamus sinicus by multistep treatments with organic-inorganic and mild-acidic-alkaline solvents. The structural characteristics of the isolated hemicelluloses, lignin, and LCC fractions were investigated.Nine soluble polysaccharide fractions were sequentially extracted with hot water (80,100, and120℃, respectively) and60%aqueous ethanol (containing0.25,0.50,1.00,2.00,3.00, and5.00%NaOH, respectively) at80℃for3h from dewaxed bamboo (D. brandisii) sample, and their chemical compositions and physicochemical properties were examined. The sequential treatments yielded20.6%soluble polysaccharides of the dry dewaxed bamboo material. Molecular weight and neutral sugars analyses revealed that the soluble polysaccharides were mainly composed of arabinoglucuronoxylans and starch. Spectroscopy analyses suggested that the isolated arabinoglucuronoxylans from D. brandisii could be defined as a linear (1â†'4)-β-linked-xylopyranosyl backbone to which a-L-arabinofuranose units and/or short chains of4-O-methyl-glucuronic acid were attached as side residues via α-(1â†'3) and/or a-(1â†'2) linkages.Five soluble hemicelluloses fractions were sequentially isolated with80%ethanol (containing0.025M HC1and0.5%NaOH, respectively), and alkaline aqueous solutions (containing2.0,5.0, and8.0%NaOH, respectively) at75℃for4h from dewaxed D. sinicus, and their structural features were determined. The sequential treatments yielded16.6%soluble hemicelluloses of the dry dewaxed bamboo sample, amounting to94.5%of the total hemicelluloses content in the bamboo material. Neutral sugar analysis indicated that the soluble hemicelluloses were mainly composed of arabinoglucuronoxylans, followed by minor amount of starch. Spectroscopy analyses indicated that the isolated hemicelluloses from D. sinicus could be defined as a linear (1â†'4)-β-linked-xylopyranosyl backbone to which a-L-arabinofuranose and/or4-O-methyl-glucuronic acid units were attached as side chains via α-(1â†'3) and/or α-(1â†'2) linkages.Nine lignin fractions from D. brandisii were sequentially isolated with hot water (80,100, and120℃, respectively) and60%aqueous ethanol solutions (containing0.25,0.5,1.0,2.0,3.0, and5.0%NaOH, respectively) at80℃for3h. The sequential treatments yielded82.7%soluble lignin based on the total lignin content in the dry dewaxed bamboo sample. Molecular weight and purity analyses revealed that the lignin fractions isolated by hot water (L1, L2, and L3) had lower weight-average molecular weights (between1350and1490g mol-1) and contained much higher amounts of associated hemicelluloses (between9.3and22.3%), while the lignin fractions isolated by alkaline aqueous ethanol (L4, Ls, L6, L7, L8, and L9) had higher weight-average molecular weights (between2830and3170g mol-1) and contained lower amounts of associated hemicelluloses (between0.6and1.7%). Spectroscopy analyses showed that the bamboo lignin was typical grass lignin, consisted of p-hydroxyphenyl, guaiacyl, and syringyl units. The major interunit linkages presented in the bamboo lignin isolated with alkaline aqueous ethanol were β-O-4’ aryl ether linkages (about74.3%), followed by β-β’ resinol-type linkages and β-1’ spirodienone-type linkages (both for7.8%), together with lower amounts of β-5’ phenylcoumaran (6.8%) and p-hydroxycinnamyl alcohol end groups (3.1%). In addition, a small percentage (1.0%) of the lignin side-chains was found to be acetylated at the y-carbon, predominantly over syringyl units.Five lignin fractions were isolated from D. sinicus by sequential treatments with80%ethanol containing0.025M HCl,80%ethanol containing0.5%NaOH, and aqueous alkaline solutions (containing2.0,5.0, and8.0%NaOH, respectively) at75℃for4h. The sequential treatments yielded80.9%lignin based on the total lignin content in the dewaxed bamboo sample. It was found that the bamboo lignin fractions isolated by ethanol had lower weight-average molecular weights (1360-1380g mol-1) and contained much higher amounts of associated hemicelluloses, while the lignin fractions isolated by aqueous alkaline solutions had higher weight-average molecular weights (5300-6040g mol-1) and contained lower amounts of associated hemicelluloses. Spectroscopy analyses indicated that the bamboo lignin was a typical grass lignin, consisting of p-hydroxyphenyl, guaiacyl, and syringyl units. The major interunit linkages presented in the obtained bamboo lignin were β-O-4’ aryl ether linkages, together with lower amounts of β-β’, β-5’, and β-1’ linkages. Additionally, a small percentage of the lignin side-chain was found to be acetylated at the y-carbon, predominantly at syringyl units.Two lignin fractions (MWL, DSL) were isolated with successive treatments of dioxane and DMSO from dewaxed and ball milled bamboo (D. sinicus) sample, and the two-step treatments yielded52.1%lignin based on the total lignin content in the dewaxed bamboo sample. Spectroscopy analyses indicated that the bamboo lignin was a typical grass lignin, consisting of p-hydroxyphenyl, guaiacyl, and syringyl units. The major interunit linkages presented in the obtained bamboo lignin were β-O-4’ aryl ether linkages, together with lower amounts of β-β’, β-5’, and β-1’ linkages. In addition, tricin was detected to be linked to lignin polymer through β-O-4’ linkage in the bamboo. Futhermore, phenyl glycoside and benzyl ether LCC linkages were clearly detected in bamboo (D. sinicus), whereas the y-ester LCC linkages were ambiguous due to the overlapping NMR signals with other substructures.The cellulose-lignin (CL) and xylan-lignin (XL) fractions were fractionated by a completely dissolution of dewaxed and ball milled bamboo (D. brandisii) sample in DMSO/TBAH solvent and followed by precipitation in deionized water. The yields of CL and XL fractions were58.2%and36.5%, respectively. Chemical composition analysis indicated that CL was composed of82.8%polysaccharides and14.2%lignin, while XL was composed of56.4%polysaccharides and41.4%lignin. Spectroscopy analyses indicated that the fraction XL was composed of hemicelluloses and lignin. The method based on DMSO/TBAH solvent for isolating the compositions of lignocellulosic cell wall was worked under mild conditions, which did not result in cleavage of the covalent bonds in the cell wall, and thus can be used as a novel and efficient method for the isolation and characterization of cell wall compositions and LCC from lignocellulosic biomass. |
PDF Full Text Request