醋酸纤维素反渗透膜材料的溶液性质

本文采用 IR、粘度测量、Huggins 方程和 MCALLISTER 方程表征,计算机拟合非线性方程组等方法研究了醋酸纤维素—丙酮溶液中各种添加剂对醋酸纤维素和丙酮的相互作用。结果表明,添加剂与丙酮有一定的相容性或部份相容性,与醋酸纤维素有一定的氢键或亲核作用。添加剂与醋酸纤维素之间的相互作用强烈地影响着醋酸纤维素的形态结构和分子之间的相互作用力。     

醋酸纤维素反渗透膜铸膜溶液的研究

醋酸纤维素是目前世界上应用最为广泛的反渗透膜材料,醋酸纤维素-丙酮溶液法成膜是最简单、最经济的成膜疗法,但目前有关其铸膜溶液的研究还远远不够。添加剂是铸膜溶液的重要组成之一,对于分离膜微孔结构的形成有着重要的意义。为此本文采用水、甲酰胺、磷酸、甘油、正丙醇作为添加剂,研究了它们对于醋酸纤维素-丙酮溶液结构与性质的影响。实验部分原料采用上海群力塑料厂生产的醋酸纤维素(CA),取代度为2.42,并采用去离子水和各种化学纯试剂:丙酮、磷酸、甲酰胺、正丙醇和甘油。IR分析采用Analect RFX-65型红外光谱仪,傅里埃变换迭加64次。     

EC/CA共混物的相容性和热稳定性

EC/CA共混物的相容性和热稳定性;乙基纤维素;醋酸纤维素;溶液共混;相容性     

阳离子化纳米纤维素晶体增强壳聚糖复合膜的制备及性能

利用水相连续法实现了纳米纤维素晶体(NCC)的高碘酸钠氧化及阳离子化,然后将阳离子化纳米纤维素晶体(CDAC)悬浮液与壳聚糖(CTS)醋酸溶液混合,并采用流延法制得壳聚糖-纳米纤维素(CTS-CDAC)复合膜。采用红外光谱(FT-IR)、透射电镜(TEM)、X射线衍射(XRD)、Zeta电位及粒径分析表征了改性前后NCC的结构与性能,并研究了制得的CDAC悬浮液与CTS醋酸溶液混合时的相容性及CTS-CDAC复合膜中CDAC质量分数对复合膜力学性能、水溶胀性的影响。结果表明:CDAC悬浮液与CTS醋酸溶液混合时相容性良好,CDAC在CTS基质中分散均匀,CTS-CDAC复合膜的力学性能较纯CTS膜明显提高。当复合膜中CDAC的质量分数为12%时,拉伸强度达到最高。另外,CTS-CDAC复合膜在水中的溶胀度较纯CTS膜明显降低,稳定性变好。     

钛醋酸纤维素反渗透膜的性能

本文研究了钛醋酸纤维素(TiCA)为膜材料的制膜工艺和添加剂对膜性能的影响,评价了制膜工艺对膜性能的关系。结果表明,不同含钛量的钛醋酸纤维素(钛0.44～2.20％),只要采用合适的添加剂和配方都能获得脱盐率为(90～99％),水通量为1·8～3·6ml/cm~2h的膜。钛纤维素适用于较高的进料温度,耐氯性能好。     

氰乙基醋酸纤维素及其膜的结构与性能

采用红外光谱、X-射线、扫描电镜和凝胶渗透色谱等方法研究了氰乙基醋酸纤维素及膜的结构与性能。试验结果表明,氰乙基醋酸纤维素具有分子量分布均勻、溶解性能好的一种无定形纤维素衍生物。氰乙基醋酸纤维素制备的膜水通量和脱盐率不仅比醋酸纤维素膜有所增加,并且有优异的耐微生物性能。研究了微生物侵蚀与乙酰基损失和膜的结构变化,并讨论了总取代度与乙酰基和氰乙基取代度对膜性能的影响。     

联苯类液晶改性纤维素膜的制备及其抗紫外性能

以1,6-二溴己烷、氰基联苯酚和N-甲基咪唑为主要原料，合成含有咪唑基团的联苯类液晶（CbP）。以离子液体1-烯丙基-3-甲基咪唑氯盐（AMIM·Cl）为溶剂，将木浆纤维素（WPC）与CbP共混得到铸膜液，再通过浸渍沉淀相转化技术将铸膜液制成纤维素液晶膜（WPC/CbP）。采用哈克流变仪对溶液性能进行表征，用傅里叶红外光谱（FT-IR）、X-射线光电子能谱（XPS）、差示扫描量热（DSC）等对膜结构和性能进行表征。结果表明，CbP的引入改变了纤维素分子内及分子间的氢键作用，提高了纤维素膜的热稳定性。当CbP在铸膜液中的质量分数为3%时，溶液黏度最低。与纯纤维素膜相比，此WPC/CbP膜的拉伸强度提高了27.56%，紫外光透光率降低了35%左右。     

微纳米纤维素功能膜在能源与环境领域的应用

探寻绿色清洁的资源与材料以维持高效的社会经济增长是未来数十年人们面临的最大挑战之一. 可持续资源与绿色材料的开发是降低传统化石能源与材料比重的最有前途的方案. 纤维素作为一种可持续发展、 可生物再生、 储量丰富且低成本的天然高分子聚合物, 在众多领域中具有广泛的应用, 并且纤维素可以加工成各种构型, 包括气凝胶、 泡沫、 海绵和薄膜等. 本文介绍了不同形态的纤维素及其衍生物组装而成的功能膜在能源与环境中的应用, 综述了微纳米纤维素及其衍生物在先进功能化储能器件方面的最新进展和制备方案, 以及在用于水处理的膜分离技术中的应用, 其中重点讨论了微纳米纤维素及其衍生物功能膜在电池、 电容器及水处理等领域中的作用, 如隔膜、 柔性电极膜和分离膜等. 此外, 还对纤维素及其衍生物功能膜的未来发展进行了总结和展望.     

纤维素/甲壳素共混膜的结构表征与抗凝血性能

以 6wt %NaOH 4wt%尿素为纤维素的新溶剂 ,采用溶液共混法制备出纤维素 甲壳素共混膜 ,为甲壳素在碱性溶液中制膜提供了新的方法 .红外光谱、X 射线衍射、扫描电镜和力学性能、抗凝血性能测试结果表明 ,共混膜中甲壳素含量低于 4 0wt%时 ,纤维素与甲壳素分子间具有良好的相容性 ;在纤维素中引入适量甲壳素可提高共混膜的抗张强度 ,共混膜的干、湿态抗张强度在甲壳素含量 10wt%时最大 ,其值分别为 89 1MPa和 4 3 7MPa ,比纯态纤维素膜的干、湿态抗张强度分别提高了 6 7%和 11 5 % ;甲壳素的引入可明显降低血小板在共混膜表面的粘附、凝聚与变性 ,增大共混膜的抗凝血参数 ,甲壳素含量达到 5 0wt%时 ,该共混膜具有良好的抗凝血性能     

一种两亲性纤维素衍生物应用于毛细管电泳分离的研究

本文以纤维素为原料,合成了一种两亲性纤维素衍生物十二烷基疏水改性季铵化纤维素。将该衍生物用作毛细管电泳背景电解质的添加物,在pH=3.0~12.0的范围内能产生稳定的阳极电渗流,可应用于芳香酸和磺胺类药物的快速分离,对中性化合物烷基苯酮同系物也有一定的分离效果。实验结果表明,该两亲性纤维素衍生物不但能调节电渗流的大小和方向,而且可与分离对象发生疏水相互作用,可用于不同荷电性质化合物的电泳分离。     

Acetylation of cellulose I and II studied by limiting viscosity and X-ray diffraction

When cellulose triacetates and some hydrolyzed acetates are boiled in 2.5N hydrochloric acid there is no residue. Under the same conditions cellulose is hydrolyzed, and a residue is obtained with a limiting viscosity that is related to the average length of the cellulose crystallites. These findings are combined to develop a method for studying the progress of acetylation through the amorphous portion of cellulose and into the crystallites, and to investigate the relative reactivities of cellulose I and cellulose II. Acetates were made from cotton and wood cellulose by a “fibrous” (heterogeneous) esterification involving sulfoacetic acid or perchloric acid catalyst in acetic acid-acetic anhydride; the final acetyl contents (10–41%) were attained by stopping the reaction at various points short of the triester (rather than by hydrolyzing a triester). When these acetates were boiled in 2.5N HCI they did not disappear completely, and the residues were cellulose I, indicating that cellulose acetate had been removed. With increasing acetyl the yield of residue decreased, and beyond about 33% acetyl the viscosity and x-ray measurements showed that the length and width of the crystallites decreased. However, when a nonsolvent such as toluene was added to the acetylation medium, the limiting viscosity did not change over the same acetyl range (up to 40%). Samples of varying acetyl values were taken during a regular acetylation of cotton linters in a mixer with sulfuric acid catalyst. X-ray studies of the residues obtained by boiling the acetates in 2.5N HCI revealed the presence of unreacted cellulose I even after 40% acetyl had been reached. This explains why the manufacture of cellulose esters from cellulose I requires complete esterification before they are hydrolyzed to the desired acetyl level. It was shown that there is a distinct difference between the acetylation reactivity of cellulose I and cellulose II. This indicates the importance of avoiding cellulose II formation during the refinement of cellulose for the manufacture of cellulose acetate in a process involving activation with acetic acid.     

4.3 Degradation and modification of cellulose acetates by biological systems

A survey is given on recent findings in the enzymology of cellulose acetate degradation. Acetyl esterases have been identified as the principal enzymes, initiating cellulose acetate degradation as a prerequisite for endoglucanase-catalyzed cellulose acetate depolymerisation. Acetyl esterases are provided by nature to deacetylate naturally occurring partly acetylated polysaccharides, i.e. xylan and chitin. Accordingly they are not designed to attack high DS cellulose acetate. Under these circumstances acetyl esterases require a pretreatment of cellulose acetate, leading to some reduction in DS, in case highly substituted material should be degraded. One of these treatments is composting under the conditions of which a partial deacetylation may occur under the action of heat and high pH, facilitating the accessibility for acetyl esterases. However from the present knowledge it cannot be excluded that certain microbial specialists exist, being capable to degrade high DS cellulose acetate.     

Characterization of cellulose acetates by nuclear magnetic resonance

An NMR method for determining the distribution of acetyl groups in cellulose acetates was developed. Treatment of cellulose acetates with acetyl-d₃ chloride gave products having simple spectra which could be analyzed quantitatively to give the distribution of acetyl groups in the original sample. The method was applied to studying (1) the hydrolysis of cellulose triacetate with ammonia, (2) the acetylation of cellulose acetate with acetyl chloride, and (3) the acetylation of cellulose acetate with acetic anhydride.     

Effect of the solvent nature on the rheological properties of concentrated solutions of various polymers

The paper compares the viscous, high-elastic and viscoelastic properties of solutions in various solvents of four polymers (polyisobutylene, polystyrene, polymethyl methacrylate and acetyl cellulose) differing in chain rigidity and the intensity of molecular interaction, over a wide range of compositions for the linear region of the mechanical behaviour of these systems. For solutions of polyisobutylene and polystyrene, the effect of the nature of the solvent on the viscosity is determined by the inherent viscosity of the solvent and by the fact that solutions under isothermal conditions are not in corresponding states with respect to their glass transition temperatures. The high-elasticity modulus of polyisobutylene and polystyrene solutions is independent of the nature of the solvent and of temperature. This indicates that the fluctuating network of entanglements is insensitive to the nature of the solvent and that the free volume plays the determining role in the behaviour of these solutions. Solutions of acetyl cellulose and polymethyl methacrylate are characterized by a very strong dependence of the viscosity on the nature of the solvent (which cannot be explained by notions valid for solutions of the first two polymers) and also by a change in the high-elasticity modulus with variation in the nature of the solvent and temperature. This proves that the properties of solutions of polar polymers are determined both by the free volume and the density of the fluctuating network, which changes with the solvent and temperature. The shape of the relaxation spectra of solutions of various polydisperse polymers in solvents of different natures is the same, while the specific properties of the solutions are associated with the position of the spectra on the time scale, which determines the fundamental constants of the solutions, viz. the zero shear viscosity and the initial high-elasticity modulus.     

Influence of water on cellulose-EMIMAc solution properties: a viscometric study

The influence of water on cellulose dissolved in 1-ethyl-3-methylimidazolium acetate (EMIMAc) is analysed by measuring steady state viscosity of dilute solutions. The goal is to determine: (a) the maximal water content allowing keeping cellulose dissolved (in dilute regime) and (b) the influence of water on solution flow and cellulose hydrodynamic properties. Mixing EMIMAc and water is exothermal and EMIMAc-water viscosity does not obey a logarithmic mixing rule suggesting strong interactions between the components. Newtonian flow of cellulose-EMIMAc-water solutions was recorded at water concentrations below 15 wt% and a shear thinning was observed for higher water content. It was suggested that above 15 wt% water cellulose is not completely dissolved: swollen aggregates form a sort of a “suspension” which is structuring under shear. Cellulose intrinsic viscosity showed a peak at 10 wt% water-90 wt% EMIMAc. It was hypothesised that the addition of water leads to the formation of large cellulose aggregates due to the preferential cellulose–cellulose interactions.     

氰乙基醋酸纤维素乙酰基含量分析

研究了Eberstadt皂化滴定法分析氰乙基醋酸纤维素中乙酰基含量的适用性。控制合适的测试条件,可以使测试结果的精度达到±0.23％,基本上达到分析醋酸纤维素的精度。红外分析、残重分析和混合物分析表明在测定过程中,氰乙基也参加了反应,但氰乙基的反应对乙酰基含量的测定结果没有影响。     

4. Characteristics of cellulose acetates 4.1 Characterization and physical properties of cellulose acetates

An overview is provided of the basic features of cellulose acetate of various degree of substitution in the solid and liquid crystalline state as well as in solution. These features represent a necessity for an understanding of the properties of these cellulose derivatives and further for mixed esters, which are not presented in this paper. Specifically, the crystal structure of cellulose triacetate will be addressed as well as structures in dilute and semi-dilute solutions. Thermal, viscoelastic and further properties in the solid state are discussed as well as flow behavior of solutions and their application in molecular weight determination, including false viscosity of commercial 2.5 cellulose acetates.     

Preparations of regioselectively methylated cellulose acetates and their 1H and 13C NMR spectroscopic analyses

Seven possible regioselectively methylated cellulose acetates (RS‐MCAs)—2,3,6‐tri‐O‐methyl cellulose acetate, 3,6‐di‐O‐methyl cellulose acetate, 2,6‐di‐O‐methyl cellulose acetate, 2,3‐di‐O‐methyl cellulose acetate, 6‐O‐methyl cellulose acetate, 3‐O‐methyl cellulose acetate, and 2‐O‐methyl cellulose acetate—were prepared for the first time from chemically synthesized cellulose derivatives obtained by cationic ring‐opening polymerization and then were analyzed by ¹H and ¹³C NMR spectroscopy. The chemical shifts of ring protons and carbons were influenced by substituent groups (methyl or acetyl) and clearly reflected the pattern of substituent distribution in anhydroglucose units. These data may conveniently be used for the determination of the substituent distribution of methyl cellulose. The synthesized RS‐MCAs also may be used for the elucidation of the structure–property relationship. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4167–4179, 2002