【作者】 程合丽；

【导师】 詹怀宇；

【作者基本信息】 华南理工大学 ， 制浆造纸工程， 2011， 博士

【摘要】 木质纤维是造纸行业的主要原料,主要由纤维素、半纤维素和木质素三大组分构成。然而,在碱法制浆过程中,大部分半纤维素随木质素进入黑液,不但造成资源的浪费,还给黑液碱回收带来困难。与制浆造纸相结合的生物质精炼的提出为实现资源的最大化利用开辟了新的途径,即在制浆之前将半纤维素预先分离,用以生产高附加值的产品,替代化石基燃料或合成材料,一定程度上缓解日益严重的能源危机,剩余原料仍用于制浆造纸。基于上述理念,本文以玉米秆为研究对象,利用不同的方法分离出其中的半纤维素,考察了分离半纤维素后玉米秆的制浆造纸性能。对分离得到的半纤维素的结构进行了探索,并将其用于木聚糖硫酸酯的合成,研究了木聚糖硫酸酯的抗凝血效果。利用不同浓度的NaOH溶液在不同温度下对玉米秆中半纤维素进行了提取,检测了提取液中糖类的组分及含量,对提取半纤维素后的玉米秆进行碱法制浆及纸浆TCF漂白,并考察了预提取对制浆黑液中二氧化硅含量的影响。研究发现玉米秆半纤维素提取液的主要组分为木聚糖,随着温度的升高及碱浓的增大,半纤维素得率逐渐上升;经半纤维素提取后,玉米秆烧碱-蒽醌浆的物理性能如紧度、裂断长及耐破指数有不同程度的降低,但白度提高,撕裂指数也明显增大,TCF漂白浆变化趋势与未漂浆相似。制浆前碱预提取半纤维素可以显著降低黑液中二氧化硅含量,在液比1:5,碱浓为100g/L,温度为75OC,提取时间为2h时,二氧化硅去除率可达80%以上,此时半纤维素得率为88.2%。利用相同摩尔浓度的KOH和NaOH溶液在相同温度、时间及液比的条件下提取半纤维素,比较了预提取效果及其后的制浆漂白性能,发现摩尔浓度相同时,KOH溶液比NaOH溶液更有利于半纤维素的溶出,而且所得纸浆的物理性能比NaOH为抽提溶剂时要强。对提取半纤维素后玉米秆烧碱蒽醌浆的微观结构进行了表征,发现碱预提取能够降低纸浆纤维表面有半纤维素和木质素特征的物质的含量,暴露出更多的纤维素纤维,对其后的纸浆漂白十分有利。利用热水提取玉米秆中半纤维素,研究了温度、保温时间的变化对糖类组分的溶出及其降解产物糠醛和羟甲基糠醛生成的影响。随着温度的升高及保温时间的增加,提取液中各糖得率均呈先升高后降低的趋势,糠醛和羟甲基糠醛的含量则始终上升;采用H-因子对糖类的溶出和糠醛、羟甲基糠醛的生成进行了描述,结果表明为获取尽可能多的半纤维素多糖,LogH应控制在3.10-3.15之间;采用Saeman模型研究了戊聚糖降解的动力学过程,得出戊聚糖降解和戊糖降解的活化能,分别为170.87kJ/mol和154.58 kJ/mol,根据糖类溶出规律、糠醛和羟甲基糠醛生成规律确定出热水预提取的最佳工艺条件为160保温180min,此时提取液中总糖和戊糖得率分别为62.2%（对原料中半纤维素）和60.5%（对原料中戊聚糖）,在此条件下对热水提取后的玉米秆进行制浆漂白,发现热水提取后玉米秆制浆漂白性能下降。以KOH溶液为溶剂,从玉米秆中分离出半纤维素,利用浓度为10g/L的H₂O₂溶液对分离的半纤维素进行纯化,研究了半纤维素的主要化学组分,采用UV、FT-IR、TG、GPC、NMR等测试技术对半纤维素的结构进行了表征,结果表明所得半纤维素为（1→4）-β-D联接的木聚糖为主链、同时在C2或C3的羟基上含有α-L-阿拉伯糖的阿拉伯糖基木聚糖。以分离的半纤维素为原料,在离子液体中与丁二酸酐酯化反应,利用FT-IR及¹H NMR对酯化产物结构进行了表征,产物有较强的吸附重金属离子的能力。以自制半纤维素为原料,LiCl为催化剂,与三氧化硫?吡啶复合物在均相体系中酯化反应合成木聚糖硫酸酯,研究了反应溶剂（DMF、FA和DMSO）、反应温度、反应时间以及三氧化硫?吡啶复合物与木糖单元的摩尔比对产物取代度及分子量的影响。结果显示,随着反应温度的升高及反应时间的延长,产物的取代度和分子量有不同程度的下降;随着摩尔比的增大,酯化产物的取代度迅速增大,以DMF和FA为反应溶剂所得产物的分子量增大,而以DMSO为溶剂时产物的分子量随摩尔比的增加而降低。利用UV、FT-IR、TG、GPC、NMR和AFM对木聚糖硫酸酯的结构和理化性质进行了研究。木聚糖硫酸酯的紫外光谱与抗凝血药物肝素钠有相同的吸收峰,红外光谱在1260cm^-1和810cm^-1处出现新的吸收峰,说明硫酸基团已成功引入半纤维素,TG结果表明经酯化后,产物热稳定性略有下降,分解温度比半纤维素低;NMR分析结果表明酯化反应主要在C2、C3的羟基上进行,且C2位上羟基的硫酸化能力优于C3;AFM观察结果发现分子量大的样品能够形成多孔网状钠米超薄膜,分子量较小时,膜表面较为光滑且很难发现孔洞。对木聚糖硫酸酯的抗凝血活性进行了研究,考察了取代度和分子量对抗凝活性的影响,对抗凝机理及构效关系进行了研究,发现只有在取代度达到一定值后木聚糖硫酸酯才具有抗凝血活性,且主要是通过影响内源性凝血途径起到抗凝的作用。当木聚糖硫酸酯取代度大于1时,用量仅为5μg/mL即有良好的抗凝血效果,达到甚至超过肝素钠的作用效果。更多还原

【Abstract】 Lignocellulose, which is made up of cellulose, hemicellulose and lignin, is the principal raw material of papermaking industry. However, during the process of alkaline pulping, a majority of the hemicellulose is dissolved in black liquor along with lignin, causing a waste of resources and, more importantly, bringing difficulties to alkali recovery. The development of Integrated Forest Product Biorefinery （IFBR） opened up a new way for maximizing the utilization of fibrous resources by extracting hemicellulose before pulping, hemicellulose extracted can be used for making value-added products which can replace the petrochemical-based fuel or materials to some extent. After hemicellulose extraction, the materials left can still be used for papermaking. Based on the above-mentioned concept, corn stover was used in this study, different methods were adopted for the extraction of hemicellulose, the remains were used for pulping and bleaching after the isolation of hemicellulose. Structure of the isolated hemicellulose was investigated and then the hemicellulose was used for the synthesis of xylan sulfate, anticoagulant activity of the xylan sulfates was studied.Hemicellulose was extracted with sodium hydroxide under different temperatures, compositions and content of the saccharides in the extract were detected, the remains were used for Soda-AQ pulping and TCF bleaching, the content of silicon dioxide in pulping liquor was determined. It was found that the main composition of the extract was xylan and the yield of hemicellulose increased with the increase of temperature and alkali concentration. Physical properties of the pulp from hemicellulose extracted corn stover, such as density, breaking length and burst index, were decreased, but brightness and tear index were improved, properties of TCF bleached pulp had similar variation tendency with unbleached pulp. The content of silicon dioxide in pulping liquor was dramatically decreased when the extraction of hemicellulose conducted before pulping. While extraction lasted 2h under 75OC with solid to liquid ratio 1:5 and alkali concentration 100g/L, more than 80% of the silicon was removed and over 88% of the hemicellulose was recoverd.Potassium hydroxide（KOH） and sodium hydroxide（NaOH） with the same molarity were used for extracting hemicellulose under the same temperature, holding time and solid to liquid ratio, differences of pulping and bleaching performance were compared, results suggested that KOH was more effective in dissolving hemicellulose than NaOH when the molar concentration was equal, furthermore, physical properties of the pulp was better than the one using NaOH as the extraction solvent. Microstructure of the fibers from Soda-AQ pulp of the hemicellulose extracted corn stover was analyzed, the content of the substances with hemicellulose and lignin characteristics on the surface of the fibers was decreased after alkaline extraction, thus more cellulose fibers can be exposed, making subsequent bleaching much easier.Hot water was also used for the extraction of hemicellulose from corn stover, the effect of the variation of temperature, holding time on the dissolving of saccharides and generation of furfural and hydroxymethylfurfural（HMF） was studied. With the increase of temperature and holding time, yields of the saccharides in the extract were increased firstly, then decreased, the contents of furfural and HMF were increased throughout the whole extraction. H-factor was adopted to describe the dissolving of the saccharides and the generation of furfural and HMF, in order to obtain hemicellulose-derived polysaccharides as much as we could, LogH should be controlled between 3.10 and 3.15. Saeman model was used to study the kinetic process of pentosan degradation, kinetic equations for pentosan degradation and furfural generation were built, the activation energy was 170.87kJ/mol and 154.58 kJ/mol for the degradation of pentosan and pentose respectively. Based on the variation law for polysaccharides dissolving and furfural, HMF generation, the optimized process for hot water extraction was 160OC for 180min., 62.2% of total saccharides（based on the content of hemicellulose of corn stover） and 60.5% of total pentose（based on the content of pentosan in corn stover） were obtained under this condition. Pulping and bleaching were conducted after hot water extraction with the optimized condition, results showed that pulping performance was not as good as the one without hot water extraction, however, bleachability of pulp was improved compared with the control.Hemicellulose was extracted from corn stover with KOH solution, H2O2 with the concentration of 10g/L was used for further purification. Chemical composition of the hemicellulose was studied, UV, FT-IR, TG, GPC and NMR were adopted to investigate the structure, it was found that corn stover hemicellulose was an arabinoxylan mainly consisting of （1→4）-β-D-xylan backbone substituted in O-2 and/or O-3 byα-L-arabinose residue. Esterification reaction was conducted between hemicellulose and butanedioic anhydride in ionic liquid,the product was characterized by FT-IR and 1H NMR and had preferable ability for absorbing heavy metal ions.Self-prepared hemicellulose was used for the synthesis of xylan sulfates with sulfur trioxide?pyridine complex in homogeneous system, the reaction was catalyzed by LiCl. The effects of solvent（DMF, FA, DMSO）, temperature, reaction time and molar ratio（SO₃·Pyridine: xylose） on the degree of substitution（DS） and molecular weight（Mw） were studied. Results suggested that DS and Mw were decreased to some extent with the increase of temperature and the extension of reaction time; DS increased substantially with the increase of molar ratio, while Mw of the products also increased with the increase of molar ratio when DMF and FA were adopted as the reaction solvent, when the reaction solvent was DMSO, Mw decreased.UV, FT-IR, TG, GPC, NMR and AFM were chosen to study the structure and physicochemical properties of xylan sulfates. UV spectra of xylan sulfates were similar to that of anticoagulation medicine, sodium heparin, new peaks appeared around 1260cm^-1 and 810cm^-1, suggesting sulfate groups were successfully introduced to hemicellulose, TG analysis indicated that xylan sulfate was less stable than hemicellulose, decomposition temperature was slightly lower than that of hemicellulose. NMR analysis showed that sulfation was maily happened on hydroxy groups of C2 and C3, and the sulfation ability of the hydroxy groups of C2 was better than htat of C3. Results from AFM indicated that multiporous nano ultrathin film could be formed from xylan sulfate with higher Mw, when Mw was lower, surface of the film was smooth and holes were not easy to find out.Anticoagulant activity of the xylan sulfates was studied and the effect of DS and Mw on anticoagulant activity was investigated, anticoagulant mechanism and structure-activity relationship were also studied, results showed that, only when DS reached certain value, xylan sulfate had anticoagulant activity. Anticoagulant function of xylan sulfate was obtained through intrinsic coagulation pathway. As the DS value of xylan sulfate was above 1 and the dosage was 5μg/mL, the anticoagulant function was the same or even better than that of sodium heparin.更多还原