| 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. |
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