【作者】 史正军；

【导师】 孙润仓；

【作者基本信息】 北京林业大学 ， 林产化学加工工程， 2013， 博士

【摘要】 本文选择在我国南方地区广泛分布的两种大型工业用丛生竹(甜龙竹、巨龙竹)为研究对象,采用有机-无机、中性-酸性-碱性相结合的多步骤抽提方式,从竹材原料中抽提出木质素、半纤维素、木质素-碳水化合物复合物(LCC)样品,结合湿法化学和现代仪器分析手段,从分子水平系统表征了竹材木质素、半纤维素、木质素-碳水化合物复合物的化学结构特征。为研究甜龙竹半纤维素的化学结构特征,选择热水(80、100、120℃)、60%碱性乙醇溶液(含0.25、0.5、1.0、2.0、3.0、5.0%NaOH)分步抽提脱蜡的甜龙竹原料,得到九个半纤维素样品。研究表明,热水和碱性乙醇连续抽提可以分离得到占原料干重20.6%的半纤维素。甜龙竹热水和碱性乙醇可溶性聚糖的主要化学组分是聚阿拉伯糖木糖,同时含有一定量的淀粉。核磁共振分析结果表明,甜龙竹半纤维素样品的分子主链是(β-1→4)-聚木糖,侧链为a-L-阿拉伯糖和／或4-0-甲基-D-葡萄糖醛酸,侧链通过α-(1→3)和/或α-(1→2)方式连接到聚木糖分子主链上。为研究巨龙竹半纤维素的化学结构特征,采用80%酸性乙醇(含0.025M HCl)、80%碱性乙醇(含0.5%NaOH)、碱性水溶液(含2.0、5.0、8.0%NaOH)分步抽提巨龙竹秆材,得到五个半纤维素样品。乙醇和碱液多步骤抽提一共得到占原料干重16.6%的半纤维素,多步抽提所得半纤维素总量占原料半纤维素总含量的94.5%。巨龙竹乙醇和碱性水溶液可溶性聚糖的主要化学组分为聚阿拉伯糖木糖,其中醇溶性半纤维素中含有少量的淀粉。结构分析表明,巨龙竹半纤维素的分子主链是(β-1→4)-聚木糖,侧链为a-L-阿拉伯糖和／或4-0-甲基-D-葡萄糖醛酸,侧链通过a-(1→3)和/或α-(1→2)键连接到聚木糖分子主链上。为研究甜龙竹木质素的化学结构特征,采用热水(80、100、120℃)和60%碱性乙醇(0.25、0.5、1.0、2.0、3.0、5.0%NaOH)依次从竹材原料中分离得到九个木质素样品。研究结果表明,热水和60%碱性乙醇多步抽提一共得到占原料木质素总含量82.7%的木质素。其中,水溶性木质素组分含有较多的半纤维素(9.3-22.3%),分子量小(1350～1490g mol-1);而碱性乙醇可溶性木质素组分化学纯度高(含0.6-1.7%半纤维素),分子量较大(2830～3170g mol-1)。结构分析表明,甜龙竹木质素属于典型的禾草类木质素(GSH型),木质素的主要联接键为β-O-4’醚键(74.3%),其次是β-β’和β-1’联接(分别为7.8%),此外还有一定量的β-5’联接(6.8%)和少量的对羟基肉桂醇端基结构(3.1%)。研究还发现,甜龙竹木质素侧链γ碳有少部分(约1.0%)发生乙酰化。为研究巨龙竹木质素的化学结构特征,采用80%酸性乙醇(含0.025M HCl)、80%碱性乙醇(含0.5%NaOH)和碱性水溶液(含2.0、5.0、8.0%NaOH)分步抽提巨龙竹原料,得到五个木质素样品(L1、L2、L3、L4和L5)。结果表明,酸性乙醇、碱性乙醇和NaOH溶液多步抽提总计从巨龙竹中抽提出占原料木质素总量80.9%的木质素。其中,醇溶性木质素分子量较小(1360～1380g mol-1),碱溶性木质素分子量较大(5300～6040g mol-1)。结构分析结果表明,巨龙竹木质素属于典型的禾草类木质素(GSH型),木质素的主要联接键为β-O-4’醚键,其次是β-β’、β-1’和β-5’联接。此外,巨龙竹木质素苯丙烷结构侧链γ位碳与对香豆酸结合,形成对香豆酸酯。为深入研究巨龙竹木质素及LCC结构特征,在温和条件下,采用二氧六环和二甲基亚砜分步抽提球磨后的巨龙竹原料,分别得到两个有机溶剂可溶性木质素组分(MWL、DSL)。二氧六环和二甲基亚砜连续处理一共从原料中抽提出52.1%的木质素(按木质素总含量计)。结构分析表明,巨龙竹木质素属于典型的禾草类木质素(GSH型),木质素的主要联接键为β-O-4’醚键,其次是β-β’、β-1’和β-5’联接。同时,在巨龙竹木质素大分子结构中存在苜蓿素结构片段。此外,核磁共振波谱分析结果证实,巨龙竹木质素与半纤维素之间存在苯基糖苷键和苄基醚键联接,但未能证实木质素-半纤维素之间是否存在γ-酯键联接。为探索新的木质纤维原料细胞壁组分分离技术,采用DMSO/TBAH全溶体系为溶剂,在室温下溶解经脱蜡和球磨处理的甜龙竹原料,经在水中再生后得到纤维素-木质素(CL)和聚木糖-木质素(XL)两个样品。其中,CL的得率为58.2%,XL的得率为36.5%。成分分析结果表明,CL样品的聚糖含量为82.8%,木质素含量为14.2%;XL样品聚糖含量为56.4%,木质素含量为41.4%。红外光谱和二维核磁共振分析结果表明,XL既有木质素的相关信号,也有半纤维素的相关信号。由于操作条件温和,分离过程对木质纤维原料细胞壁组分结构破坏小,基于DMSO/TBAH全溶体系的组分分离技术有望发展成为一种全新的木质纤维原料细胞壁组分分离纯化新技术。更多还原

【Abstract】 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 (1→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-(1→3) and/or a-(1→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 (1→4)-β-linked-xylopyranosyl backbone to which a-L-arabinofuranose and/or4-O-methyl-glucuronic acid units were attached as side chains via α-(1→3) and/or α-(1→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.更多还原