低取代醋酸纤维素的均相合成及其水溶性

本文在离子液体中进行低取代度CA的均相合成, 得到了一系列CMA, 部分合成的CMA在水中具有良好的溶解性.     

Properties and Applications of Cellulose Acetate

Cellulose acetate is one of the most important esters of cellulose. Depending on the way it has been processed cellulose acetate can be used for great varies of applications (e.g. for films, membranes or fibers). The properties of the applied cellulose acetates are very important for these applications. A special field for using cellulose acetate is the synthesis of porous, spherical particles, so called cellulose beads. Different types of technical cellulose acetates were used and their ability to form such cellulose beads was characterized. First the different types of cellulose acetates were characterized by means of solubility; turbidity and degree of substitution. In addition the molar mass and the distribution of substituents along the polymeric chain were analyzed. Next, the cellulose beads were synthesized within an emulsion process using these different cellulose acetates. Then the properties (particle size, porosity, morphology) of the cellulose beads were determined. Finally, the relationship between the characteristic of cellulose acetates and properties of cellulose beads was investigated.     

Substituent Distribution of Cyanoethyl Cellulose

Estimation of the substitution distribution for cyanoethyl cellulose was carried out by ¹H and ¹³C NMR spectroscopic analyses after the additional acetylation. Based on the complemental function of cyanoethyl and acetyl substituents, the degree of substitution (DS) of cyanoethyl groups could be calculated from the ratios of the ¹H integrated intensities in acetyl methyl ( 1.8–2.1) and cyanoethyl methylene ( 2.6–2.9) protons, and also from the corresponding ratios for acetyl methyl carbon signals ( 19.7–21.3) and cyanoethyl methylene carbon signals ( 17.5–19.0). Good agreement was obtained between the DS values obtained from the NMR spectroscopic analyses and those determined by the conventional nitrogen content method, indicating the validity of the NMR method used. In addition, the NMR method was found to be effective in determining the positional substituent distribution by the quantitative analysis of the three cyan carbon signals ( 118–120).     

Trimethylsilylation of Cellulose in Ionic Liquids

Trimethylsilylation of cellulose in different 1,3‐dialkylimidazolium ionic liquids (IL) with hexamethyldisilazane (HMDS) as a silylating agent was investigated. Trimethylsilyl (TMSi) cellulose with a degree of substitution (DS) greater than 1 is insoluble in the IL. The maximum DS obtained depends on the nature of the anion. Carboxylate and diethylphosphate counterions gave better results than chloride or thiocyanate, which corresponds to the solubility of HMDS in the IL. Controlled silylation with stoichiometric amounts of HMDS was feasible in imidazolium carboxylates and diethylphosphate. Analysis of the substitution pattern of the silyl groups in the anhydroglucose unit (AGU) by methylation analysis gave a more homogeneous distribution under (initially) homogeneous conditions (fewer unsubstituted AGUs, fewer trisubstituted AGUs) compared to TMSi cellulose obtained in liquid ammonia.

     

Characterization of Water-Soluble Cellulose Derivatives in Terms of the Molar Mass and Particle Size as well as Their Distribution

The property profile of cellulose derivatives dissolved in aqueous solvents is not only dependent on the chemical composition (average-, molar- or regiospecific degree of substitution, as well as the substitution along the chain), solvent, temperature and concentration but also on the molar mass and the particle size. All this information can be obtained from the Mark-Houwink-Sakurada-relationship ([;gh]-M-) or the R_G-M-relationship, if these are at hand. These relationships are suitable for a specific degree of substitution. The R_G-M-relationship has only been determined and published for a few water-soluble cellulose derivatives. The prerequisite is the availability of a homologous series of samples with the same chemical composition. In this paper it is shown that only the ultrasonic degradation is able to create such a series. Due to the ability of coupled methods of analysis to acquiring absolute data, molar mass and particle size distributions have been compiled in recent years. Using such methods it was possible to determine molar mass and particle size distributions of several aqueous cellulose derivative solutions by combining a fractionation unit (size exclusion chromatography (SEC) or flow field-flow fractionation (FFFF)) with multi angle laser light scattering (MALLS) for the detection of Mw and R_G and concentration detection (DRI). Results for nonionic cellulose ethers, mixed cellulose ethers, ionic carboxymethyl cellulose, sulfoethyl cellulose, hydrophobically modified hydroxyethyl cellulose were obtained and are partially discussed with focus on the recovery of cellulose derivates after fractionation and the impact on the distribution functions.     

Selectively Dendronized Cellulose: Synthesis and Characterization

Selectively dendronized cellulose at C‐6 was synthesized homogeneously (in DMSO) and heterogeneously (in methanol) by the conversion of 6‐azido‐6‐deoxy cellulose (degree of substitution, DS 0.75) with polyamidoamine (PAMAM) dendrons possessing an ethynyl focal moiety via the copper‐catalyzed Huisgen reaction (click reaction) under mild conditions. First to third generation of PAMAM‐triazolo cellulose derivatives with DS values of up to 0.69 could be prepared, which are soluble in organic solvents (DMSO, DMF) and in water. The novel biopolymer derivatives were characterized by elemental analysis, FTIR, and NMR spectroscopic methods, showing no impurities and no conversion at the secondary positions.

     

Decolorization of Distillery Effluent Using Poly(Vinyl Chloride) and Cellulose Acetate Phthalate as Adsorbents

Decolorization of distillery effluents, using low cost polymer adsorbents, is one of the challenging areas for environmental technologists. Untreated distillery effluents are harmful to the environment, causing foul smell, spoiling fresh water sources and killing aquatic life. The color of distillery effluents have been decolorized by using polymer based adsorbents, such as poly(vinyl chloride) (PVC) and cellulose acetate phthalate (CAP), which are water insoluble, easily available, and cheap. In the present article, special emphasis is given to studies such as the effect of contact time, dosage amount, dilution, and the variation in the amount of sample on the degree of decolorization of the effluent. The decolorization of a distillery effluent was monitored by using UV/Visible spectroscopy and Fourier transform infrared spectroscopy (FTIR). From these studies, it was noticed that moderate to fair results were obtained and it was also found that CAP was a better adsorbent, compared to PVC, for decolorization of distillery effluents.     

二醋酸纤维素接枝聚己内酯的核磁共振表征

用^1H-NMR和^13C-NMR研究了二醋酸纤维素(CDA)和聚己内酯(PCL)的接枝共聚反应,确定了^1H-NMR和^13C-NMR谱中各谱峰的归属,为证明二醋酸纤维素和己内酯的接枝共聚反应提供了依据。     

Study of the reaction between 1,5-naphtalene diisocyanate and polycaprolactone in different solvents

The reaction between polycaprolactone and 1,5-naphtalene diisocyanate has been investigated in solvents with different dielectric constants and hydrogen bonding powers (toluene, ethyl acetate, ethyl methyl ketone), and in the same solvents with the addition of a catalytic amount of dimethyl sulfoxide (DMSO). The reaction was considered to proceed over two steps, the reaction of the first NCO group being faster. The course of the reaction was measured by titration of the unreacted NCO groups, ¹H- and ¹³C-NMR spectroscopy, and size exclusion chromatography. By titration only the overall reaction order and reaction rate constants could be determined. DMSO accelerated the reaction in all three solvents, which was explained by the stabilization of the activation complex by DMSO. Both steps of the reaction could be specified by NMR spectroscopy. The ratio between the reaction rate constants for the first and the second step decreased with the increased hydrogen bonding strength of the solvent and with DMSO. By SEC only the reaction of the first NCO group could be determined due to the low resolution for higher molar mass reaction products with a broad distribution. The values obtained for the first step reaction rate constants were in good agreement with NMR values. © 1995 John Wiley & Sons, Inc.     

纤维素微孔锂电隔膜的制备及性能研究

为了改善锂电隔膜的亲液性和耐高温性,以醋酸纤维素为成膜材料,利用相转化法制备了新型锂电隔膜,通过形貌和孔道结构表征、亲液性能和耐热性能测试对醋酸纤维素隔膜的基本性能进行研究,并将该隔膜装配成锂离子电池进行充放电性能测试. 结果表明,醋酸纤维素隔膜具有均匀的微孔结构,孔隙率达到65%,约为传统聚烯烃隔膜的1.5倍;纤维素材料的良好亲液性和高孔隙率结构改善了隔膜的吸液性能,其吸液率达到285%;该隔膜在150 ^oC、30 min的热处理条件下未发生明显的热收缩. 鉴于上述优点,相对于市售PE隔膜,醋酸纤维素隔膜所装配锂离子电池显示出更优的循环性能和倍率性能.     

Distribution of Substituents along the Cellulose Chain on Cellulose Xanthate and Carboxymethyl Cellulose

The distribution of substituents of cellulose xanthogenate and carboxymethyl cellulose along the cellulose chains and therefore in relation to the molecular mass can be measured using size exclusion chromatography including a multi angle laser light scattering and mass detection for determining the molecular mass of the derivative assisted by an UV- detection for determining the xanthate groups and carboxymethyl groups after derivatisation, respectively. The results investigating cellulose xanthogenate show that the temperature used in dissolving xanthogenate and in ripening viscose influences the distribution of xanthate groups in a different way; but all steps processing viscose are connected with a loss in the degree of substitution in ripening the distribution of substitution additionally becomes more even. The investigated carboxymethyl cellulose revealed different distribution of carboxylic groups in dependence on the viscosity of the CMC.     

Cellulose Derivatives Used as Chiral Stationary Phases in Capillary Gas Chromatography

Abstract

In this work, we present the first separation of enantiomers in gas chromatography (GC) using a fused‐silica capillary column containing cellulose triacetate, cellulose triphenylcarbamate, or cellulose tris(3,5‐dimethylphenylcarbamate) as the new chiral stationary phase. The separated solutes included alcohols, amine, ketone, ether, ester, and amino acid. Their column efficiency, polarity, and chiral selectivity were studied. The retention mechanism was discussed. The results showed that those derivatives had relatively high chiral recognition abilities and can be used as the chiral stationary phases in GC.     

Study on Synthesis and NMR Characterization of 2,3-O-Hydroxyethyl Cellulose Depending on Synthesis Conditions

The synthesis of hydroxyethyl celluloses with regioselective functionalization in position 2 and 3 starting from triphenylmethyl (trityl) cellulose is described. The effects of reaction conditions upon both the degree of substitution and the distribution of the hydroxyethyl moieties were investigated in detail. The interest was not only focused on regioselective functionalization within the anhydroglucose unit but also on the formation of oxyethylene side chains. To avoid the formation of oxyethylene side chains, 2-(2-bromoethoxy)tetrahydropyran was used as etherifying agent in comparison with 2-bromoethanol. By acidic hydrolysis, both protecting groups – trityl at 6 position and tetrahydropyran at the hydroxyethyl substituent – can be simultaneously cleaved off. The hydroxyethyl celluloses were characterized by one- and two-dimensional NMR spectroscopy in order to determine the substitution pattern.     

Preparation and Characterization of Nanocomposites of Carboxymethyl Cellulose Reinforced with Cellulose Nanocrystals

Summary: Cellulose nanocrystals (CNC) were extracted from Kraft pulp of Eucalyptus urograndis. The CNC were isolated by acid hydrolysis with H₂SO₄ 64% (w/w) solution, for 20 minutes at 45 °C. The morphology and crystallinity of the CNC were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. The AFM image supports the evidence for the development of crystals of cellulose in nanometric scale. These nanoparticles were used as reinforcement material in carboxymethyl cellulose (CMC) matrix. Nanocomposites films were prepared by casting. The nanocomposites were characterized by thermal (TGA) and mechanical (DMA) analyses. A large reinforcing effect of the filler was observed. The tensile strength of nanocomposites was significantly improved by 107%, the elongation at break decreased by 48% and the thermal resistance increased slightly. The improvements in thermo-mechanical properties suggest a close association between filler and matrix.     

纤维素酶降解纤维素机理的研究

纤维素是自然界中含量最多的一类碳水化合物,同时它也是地球上数量最大的可再生资源。纤维素酶是一种高活性生物催化剂,在纤维素类资源的利用方面发挥重要的作用。本文综述了纤维素、纤维素酶的分子结构和纤维素酶对纤维素的降解机理,影响酶解的主要因素以及提高酶解效率的主要措施,并对纤维素酶研究存在的问题以及今后的发展作了进一步展望。     

三醋酸纤维素/醋酸纤维素正渗透膜的制备工艺对性能的影响

通过相转变法制备了一系列三醋酸纤维素/醋酸纤维素正渗透膜,并探索了影响正渗透膜水通量的三个重要因素:膜厚度、凝胶时间、热处理过程。结果表明膜厚度为300mm、凝胶时间48 h,并经过热处理以后的正渗透膜水通量效果最佳,达到7.088 L/m~2·h。     

Analytical Investigations of Bacterial Cellulose

The cultivation of the bacterium Acetobacter xylinus AX 5 was carried out in the common Hestrin-Schramm medium containing D -glucose as C-source and citric acid as buffer component. HPLC studies proved to be convenient methods to investigate the stability and interactions of these constituents in the starting culture liquid. Within the initial sterilization step and limited by the citric acid, up to 6% of the D -glucose was partially isomerized to D-fructose and degraded to dark-yellow products. In static culture, A. xylinus AX 5 produces cellulose extracellularly on the surface of this medium. Solid-state NMR spectroscopy represents a suitable analytical method to characterize the supramolecular structure of the bacterial cellulose in never-dried, air-dried, and freeze-dried states. It could be demonstrated that the drying process reduces the degree of crystallinity in the range of about 12% without changes in the Iα/β ratio of these cellulose modifications.     

纤维素硝酸酯接枝物的FTIR光谱

作者对纤维素硝酸酯与聚甲基丙烯酸甲酯接枝共聚物的FTIR光谱进行了比较全面的定性与定量分析,并探索其在接枝共聚研究中的某些应用。     

纤维素纳米晶体薄膜的制备与表征

讨论了两种新型纤维素纳米晶体(Cellulose nanocrystal,CNC)薄膜的制备方法:浸没法和旋涂法,并利用红外反射吸收光谱(Infrared reflection absorption spectroscopy,IRRAS)和原子力显微镜(Atomic force microscopy,AFM)对其进行表征。AFM高度图显示两种工艺制备的CNC薄膜均由棒状的CNC纳米颗粒交错叠加而成。实验结果显示,旋涂法制备的薄膜更加光滑,粗糙度RMS约为2.7 nm。由于带电颗粒间斥力的存在,浸没法制备的CNC膜厚度最大约为15 nm,而旋涂法可以得到更厚的CNC薄膜,其厚度可达50 nm以上。研究CNC悬浮液浓度与旋涂法CNC膜厚之间的关系后发现,可以通过改变CNC溶液的浓度对薄膜厚度进行控制。IRRAS结果也证实随着CNC悬浮液浓度的增加,旋涂薄膜的厚度随之增加。