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羧甲基羟两基纤维素(CMHPC)经水解和乙酰化反应后,利用~1H NMR和~(13)C NMR谱确定其取代度和取代基分布,提出了纤维素葡萄糖单元上羟基的相对反应活性顺序。 相似文献
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《纤维素科学与技术》2019,(4):18-26
双取代基的氰乙基甘油醚纤维素在具有与单取代基氰乙基纤维素相近的氰乙基取代度时性能不同,但它们的FT-IR光谱图、一维核磁~1H-NMR和~(13)C-NMR光谱图信号表现高度重叠。为了能识别出它们的结构差异以辅助理解其性能区别,本研究采用对样品用三氟乙酸进行部分水解断链和残余羟基全乙酰化预处理后,在60℃下二维核磁(COSY, HSQC)NMR进行20小时的扫描谱图,实现了对氰乙基甘油醚纤维素上双取代基团的信号峰的归属,获得了平均取代度和支化结构等信息,显示甘油取代基无支化发生。证明二维核磁能有效地识别分析氰乙基甘油醚纤维素结构,增加多糖衍生物材料结构解析新手段,以期更多科研人员采用此方法应用于解析其他单取代和多取代纤维素等多糖衍生物结构。 相似文献
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~(13)C-NMR法研究醋酸纤维素的取代基分布 总被引:2,自引:0,他引:2
用常规醋酸纤维素的13C-NMR法计算取代基分布难以准确。采用先将二醋酸纤维素中的剩余羟基完全丙酰化,再用13C-NMR法测定二醋酸纤维素乙酰基的取代分布的方法,其研究结果表明,完全丙酰化的二醋酸纤维素的碳谱中羰基碳区两组三重峰可较好地分开,因而可以根据它们的面积比算出其总取代度及在2,3和6位碳原子上的取代基分布。 相似文献
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以冰醋酸为溶剂,浓硫酸为催化剂,将三醋酸纤维素水解为不同取代度的醋酸纤维素(CA),再用此醋酸纤维素同ε-己内酯(ε-CL)接枝共聚合成醋酸纤维素/聚己内酯接枝共聚物(CA-g-PCL).研究了醋酸纤维素取代度和原料配比对单体转化率(C)、接枝率(G)、接枝效率(EG)的影响,结果表明在醋酸纤维素取代度为0.7时接枝共聚反应C、G、EG可分别达到46%、238.6%、88.5%;m(ε-CL)m(CA)=51时可分别达48.3%、140.553%、58.2%,并对相应的接枝共聚物进行了FTIR和1H-NMR的表征分析. 相似文献
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由于纤维素化学结构的特殊性,不同工艺条件制备的醋酸纤维素,即使平均聚合度和酯化度相同的成品,因其乙酰基和羟基在纤维素大分子及基环中分布均一性的差异,会导致所铸反渗透膜水通量和脱盐率的不同。 相似文献
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《合成纤维》2015,(12):5-9
以实验室自制的三醋酸纤维素(CTA)为原料,研究其最佳水解条件及水解产物二醋酸纤维素(CDA)的可纺性能。结果表明:60℃下水解时间为4 h,H_2O与CTA的质量比为5∶1,催化剂H_2SO_4的质量分数为CTA的12%,可得到取代度为2.60的CDA。水解产物CDA经湿法纺丝后得到的纤维的干态断裂强度为1.45 c N/dtex,优于目前国内市售的CDA纤维。用FTIR、XRD、TG、SEM对CDA及其纤维进行分析表征,结果显示:CDA经水解和纺丝后结晶度会下降,CDA热分解温度低于CTA和纤维素;SEM照片显示CDA纤维表面有少许沟槽,断面呈圆形结构。 相似文献
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纤维素醋酸酯接枝己内酯的聚合研究 总被引:1,自引:0,他引:1
以冰醋酸为溶剂,浓硫酸为催化剂,将取代度为2 4的二醋酸纤维素水解为取代度为1 4的醋酸纤维素(CA)。以此醋酸纤维素为接枝骨架,ε 己内酯(ε CL)为接枝单体,在辛酸亚锡的引发下,合成了醋酸纤维素/聚己内酯接枝共聚物(CA g PCL)。研究了反应物纯度、原料配比、引发剂与单体摩尔比、反应时间、反应温度对单体转化率(C%)、接枝率(G%)、接枝效率(GE%)的影响。结果表明,当反应温度为140℃,单体ε 己内酯与醋酸纤维素的质量比为4∶1,引发剂辛酸亚锡与单体ε 己内酯的摩尔比为0 005,反应时间为16h,C%,GE%和G%分别为46 8%,65 2%和122 1%。 相似文献
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利用尿素对醋酸纤维素(CA)进行浸泡预处理,然后移入邻二甲苯惰性体系中进行反应。探讨合成过程中的影响因素,结果表明:预处理过程中尿素的质量分数为25%,预处理温度55℃,预处理时间5h,反应时间3.5h时,所得醋酸纤维素氨基甲酸酯(CAC)的取代度可达到0.1。FT-IR表征证明成功合成了CAC。用制备的CAC进行铸膜,CAC膜的拉伸强度及水通量要优于CA膜,并且随着取代度的提高,CAC膜的拉伸强度及水通量呈上升趋势。 相似文献
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羟丙基甲基纤维素的流变性质及热凝胶化行为 总被引:3,自引:1,他引:2
应用旋转黏度仪测试了四种羟丙基甲基纤维素(HPMC)溶液样品在不同浓度下的流变性质,并用动态旋转流变仪研究了HPMC样品的热凝胶效应。结果表明,HPMC的相对分子质量对流变性质有显著影响,而取代基的影响不很明显;同时得出了流体行为指数与浓度之间的数学模型关系式。取代基对热凝胶效应影响显著,而对不同取代度的样品系列而言,相对分子质量的影响趋势各不相同。 相似文献
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The biodegradation behavior of various cellulose acetate (CA; degree of substitution = 2.5) films that contain acids was examined by a laboratory soil burial test to clarify the effects of additives on the biodegradability of CA. The biodegradation rate of the CA films containing polyphosphoric acid, phosphoric acid, and p‐toluenesulfonic acid increased compared to that of the nonadditive CA film. CA films containing mandelic acid and maleic acid showed a small tendency to increase. Conversely, CA films containing adipic acid did not affect the biodegradability of CA. A similar experiment was carried out with a sterilization system. The acid‐containing CA film, which showed an accelerated biodegradation rate, was chemically deacetylated by contact with water in the environment and was consequently converted to a lower degree of acetyl group substitution matter that had higher biodegradability. An IR analysis suggested that this deacetylating ability of acids is correlated with the intensity of their interaction with the acetyl group of CA. In the biodegradation process, the contact efficiency of acids to CA was considerably lowered by the elution of internal acids with time. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 466–473, 2005 相似文献
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Adina Maria Dobos Iuliana Stoica Niculae Olaru Liliana Olaru Emil Ghiocel Ioanid Silvia Ioan 《应用聚合物科学杂志》2012,125(4):2521-2528
The article describes some properties of cellulose acetates (CAs) with different substitution degrees. The hydrophilic/hydrophobic properties, morphological aspects, and interface properties with red blood cells and platelets are affected by the substitution degree, synthesis conditions, history of the formed films from solutions in acetone/water nonsolvent/nonsolvent mixtures, and low pressure plasma treatment. The results obtained are useful in biomedical applications, including evaluation of bacterial adhesion onto surfaces, or utilization of CA for semipermeable membranes. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
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To study the effectiveness of photosensitizers to accelerate the degradation of cellulose acetate (CA) under ambient environment, CA (degree of substitution = 2.45) films containing benzophenone, which is one of the typical photosensitizers, were prepared and their degradative behavior by photoirradiation was examined. Decrease in molecular weight of CA and generation of carbon dioxide, carbon monoxide, and acetic acid from the CA films were observed by the irradiation of xenon arc lamp light, which was passed through a filter for cutting off the wavelength shorter than 275 nm. With increasing the concentration of benzophenone, the molecular weight of CA decreased and the generation of the degradation products from the CA films increased. These results may suggest that radical reactions of CA films proceed by photoirradiation and lead to oxidation and random cleavage of CA, and that benzophenone is an effective additive to accelerate the degradation of CA under ambient environment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
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Cellulose derivatives of carboxymethyl cellulose sodium salt (CMC), hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and enzymatically treated cellulose have been electrospun, and the microstructure of the resulting nanofibers has been analyzed by scanning electron microscopy (SEM). Before electrospinning, the solutions were characterized by viscometry and surface tension measurements, and the results were correlated with spinnability. Four different CMC derivatives, varying in molecular weight (Mw), degree of substitution (DS), and substitution pattern, have been electrospun in mixtures with poly(ethylene oxide) (PEO), and nanofibers of various characteristics have formed. The CMC‐based nanostructures, i.e., the nonwoven sheet and individual nanofibers, proved to be independent of Mw and DS but largely dependent on the substitution pattern. The nonwoven sheets varied in homogeneity, and beads appeared on the individual fibers. Depending on the chemical nature of the CMC, the extraction of PEO resulted in pure CMC nanostructures of varying appearance, indicating that the distribution of PEO and CMC in the nanofibers also varied. Two different HPMC derivatives, varying in DS, were electrospun into nanofibers. Homogeneous nonwoven sheets based on nanofibers of similar appearance are formed, independent of the substitution content of the HPMC sample. Preliminary fibers were obtained from enzymatically treated cellulose in a solvent system based on lithium chloride dissolved in dimethyl acetamide (LiCl: DMAc). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1473–1482, 2007 相似文献
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Surface activity of aqueous solutions of cellulose acetate (CA) with total degree of substitution (〈F〉) ranging from 0.58 to 0.80 was examined. Critical micelle concentration (CMC) of the aqueous CA solutions, determined from the polymer concentration dependence of surface tension (γ), is unequivocally determined by 〈F〉, and an increase in 〈F〉 of CA brings about a lowering of the CMC. From light scattering measurements on aqueous solutions of CA with 〈F〉 = 0.8 at 20°C, it was revealed that in the vicinity of the CMC the micelles in the solution consist of c. four CA molecules, which is very close to the value obtained by analysing the data obtained from the mass action model. The surface tension of aqueous solutions of CA (〈F〉 = 0.8) in the polymer concentration range above the CMC was c. 0.74 times that of pure water over the temperature range 0–80°C. 相似文献
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The thermal discharge behaviour of cellulose diacetate (CA2) (39% acetyl content) and cellulose triacetate (CA3) (44% acetyl content) films was studied at different polarizing temperatures and fields. Cellulose diacetate exhibited two peaks, one at low temperatures and the other at high temperatures, whereas cellulose triacetate exhibited only one peak. The origin of these peaks in CA2 is attributed to dipolar orientation and space charge polarization respectively, while the only peak in CA3 is due to space charge polarization. The difference in thermal discharge behaviour of CA2 and CA3 is attributed to the difference in acetyl contents of the two acetates. 相似文献