首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 125 毫秒
1.
Preparation of Polyuronic Acid from Cellulose by TEMPO-mediated Oxidation   总被引:19,自引:8,他引:11  
Various cellulose samples were oxidized by 2,2,6,6,-tetramethylpipelidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems, and the effects of oxidation conditions on chemical structures and degrees of polymerization of the products obtained were studied. In the case of regenerated and mercerized celluloses, almost all C6 primary alcohol groups were selectively oxidized to carboxyl groups, and water-soluble polyglucuronic acid (cellouronic acid) sodium salts were obtained almost quantitatively; the degrees of polymerization were influenced greatly by the amount of TEMPO added, and the oxidation time and temperatures. Cellouronic acids prepared from mercerized linter and kraft pulps had size exclusion chromatograms with two separate peaks due to higher and lower molecular weight fractions. On the other hand, only small amounts of carboxyl groups were introduced into native cellulose samples. Since polyglucuronic acids prepared from cellulose by the TEMPO–NaBr– NaClO systems regularly consist of the glucuronic acid repeating unit, differing from the conventional water-soluble cellulose derivatives, they may open new fields of cellulose utilization.  相似文献   

2.
郭立颖  史铁钧  段衍鹏 《应用化学》2009,26(9):1005-1010
以氯丙烯和N-乙基咪唑为原料合成了离子液体氯化1-烯丙基-3-乙基-咪唑盐([AEIM]Cl),利用FT-IR和1HNMR对其化学结构进行了表征。采用微波加热法溶解微晶纤维素(MCC),考察 [AEIM]Cl对纤维素的溶解性能。研究了NaOH、微波和高压等3种预处理方式对微晶纤维素的相对结晶度、聚合度及溶解率的影响。利用FT-IR、XRD、TGA和SEM分别对溶解后得到的再生纤维素的化学结构、晶型变化、热稳定性及表观形貌进行测试与分析。结果表明,合成的离子液体是目标产物,对微晶纤维素表现出很好的溶解能力,且高温高压条件下15%的NaOH水溶液对微晶纤维素处理后,得到的纤维素相对结晶度最小,聚合度最低,溶解率最高。溶解过程中纤维素没有发生衍生化反应,溶解后得到的再生纤维素的相对结晶度和微晶尺寸变小,热稳定性降低。  相似文献   

3.
The cellulose solvent dimethylsulfoxide/tetrabutylammonium fluoride trihydrate (TBAF·3 H2O) was studied as reaction medium for the synthesis of benzyl cellulose (BC) by treating the dissolved polymer with benzyl chloride in the presence of solid NaOH or aqueous NaOH solution. BC samples with degree of substitution (DS) between 0.40 and 2.85 were accessible applying different molar ratios. The studies show that both the TBAF·3 H2O concentration and the molar ratio of the reagents to repeating unit influence the DS. The solubility of the BC synthesized in a different way, however, of comparable DS is different. Structural analyses were carried out by means of FTIR-, 1H- and 13C NMR spectroscopy. SEC measurements revealed polymer aggregation in samples of low DS synthesized in a solvent containing 9.0% TBAF·3 H2O. At higher concentration of TBAF·3 H2O in the solvent, the BC samples obtained do not form aggregates. BC of high DS is crystalline and shows thermotropic liquid crystalline behavior as analyzed by means of DSC. Melting point and degradation temperature are not related to the DS.  相似文献   

4.
A cost‐effective and environmentally friendly method to dissolve microcrystalline cellulose (MCC) has been utilized. A detailed investigation of the effects of cellulose amount and solvent (aqueous NaOH) concentration on MCC solubility has been presented. In the experiments, NaOH solutions with concentrations ranging from 3.7 to 18.6 wt% have been employed to dissolve MCC with various weights. The results show that an optimal NaOH concentration range can always be found to give the best solubility of MCC having a certain weight. The solubility monotonically decreases with either the decreasing or increasing of NaOH concentration away from the optimal concentration range. In addition, the optimal concentration range of NaOH for dissolving cellulose has been shown to shrink as the amount of MCC increases. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

5.
The Young's modulus of a microcrystalline cellulose   总被引:3,自引:0,他引:3  
This research is concerned with an investigation into the determination of the micromechanical properties of particulate form of cellulose; namel microcr stalline cellulose. Using the technique of Raman spectroscop the shift in the 1095cm–1 Raman band, characteristic of cellulose, with strain is monitored and compared to the deformation of natural cellulose fibres (flax and hemp). From the values of the shift rate of the 1095cm–1 band for flax and hemp and the experimentally-determined value for microcrystalline cellulose the value for the Young's modulus of microcrystalline cellulose was estimated to be 25±4GPa. It has been shown that this value is consistent with the measured degree of crystallinity of microcrystalline cellulose. Theoretical modelling has also enabled the Young's modulus for compacted microcrystalline cellulose to be determined for fibres in either 2-D in-plane and 3-D arrangements. These values have been show to be consistent with recent direct measurements of the modulus of compacted material.  相似文献   

6.
The surface properties of several purified cellulose (Sigmacell 101, Sigmacell 20, Avicel pH 101, and Whatman CF 11) were characterised, before and after cellulase adsorption. The following techniques were used: thin-layer wicking (except for the cellulose Whatman), thermogravimetry, and differential scanning calorimetry (for all of the above celluloses). The results obtained from the calorimetric assays were consistent with those obtained from thin-layer wicking – Sigmacell 101, a more amorphous cellulose, was the least hydrophobic of the analysed celluloses, and had the highest specific heat of dehydration. The other celluloses showed less affinity for water molecules, as assessed by the two independent techniques. The adsorption of protein did not affect the amount of water adsorbed by Sigmacell 101. However, this water was more strongly adsorbed, since it had a higher specific heat of dehydration. The more crystalline celluloses adsorbed a greater amount of water, which was also more strongly bound after the treatment with cellulases. This effect was more significant for Whatman CF-11. Also, the more crystalline celluloses became slightly hydrophilic, following protein adsorption, as assessed by thin-layer wicking. However, this technique is not reliable when used with cellulase treated celluloses.  相似文献   

7.
Cold NaOH/urea aqueous dissolved cellulose was studied for the synthesis of benzyl cellulose by etherification with benzyl chloride. By varying the molar ratios of benzyl chloride to OH groups in cellulose (1.5–4.0) and reaction temperatures (65–70 °C), benzyl cellulose with a degree of substitutions (DS) in the range of 0.29–0.54 was successfully prepared under such mild conditions. The incorporation of benzyl groups into cellulose was evidenced by multiple spectroscopies, including FT IR, 1H NMR, 13C NMR, CP/MAS 13C NMR and XRD. In addition, the thermal stability and surface morphology of the benzyl cellulose was also investigated with regard to the degree of substitution. The results indicated that the benzyl cellulose product with a low DS (0.51) in the present study reached the same solubility in many organic solvents as compared to those prepared in heterogeneous media. After benzylation, the sample decomposed at a lower temperature with a wider temperature range, which indicated that the thermal stability of benzyl cellulose was lower than that of the native cellulose. In addition, benzylation resulted in a pronounced reduction in crystallinity as well as a fundamental alteration of morphology of the native cellulose.  相似文献   

8.
A Raman crystallinity index – XcRaman – characterizing the degree of crystallinity of partially crystalline cellulose I samples was created, utilizing the crystallinity dependence of CH2 bending modes. For calibration, physical mixtures containing different mass fractions of crystalline cellulose I and its amorphous form were prepared. Crystallinities from 0 to 60% were generated. Relative intensity ratios of the Raman lines I and I characterizing crystalline and amorphous parts of cellulose I correlated linearly with the mass fraction of crystalline cellulose I of the mixtures. XcRaman values of microcrystalline celluloses of different origins and varying degree of crystallinity correlated reasonably with results obtained from NMR spectroscopy (XcNMR values).  相似文献   

9.
13C CPMAS NMR investigations of cellulose polymorphs in different pulps   总被引:2,自引:0,他引:2  
In order to obtain information about the crystallinity and polymorphs of cellulose, and the occurrence of hemicelluloses in pulp fibers, wood cellulose, bacterial cellulose, cotton linters, viscose, and celluloses in different pulps were investigated by solid state 13C CPMAS NMR spectroscopy. A mixed softwood kraft pulp and a dissolving-grade pulp were treated under strongly alkaline and acidic conditions and the effect on cellulose crystallinity was studied. The presence of different crystalline polymorphs of cellulose and the amounts of hemicelluloses are considered.  相似文献   

10.
Hydrogels with high water retention can be produced from cotton cellulose. Treating aqueous suspensions of microcrystalline cellulose, lint, and powdered cellulose with mechanical pulses of various frequencies, amplitudes, and shear stresses turns them into gels.Nizami Tashkent State Pedagogical University, fax (3712)-54-92-17. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 71–73, January–February, 2000.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号