An investigation in solution acetylation of cellulose by microscopic techniques

The solution acetylation process of cellulose has been investigated by means of scanning electron and transmission microscopic techniques. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the different morphologies of cellulose acetates, which were prepared at different temperatures. Simply, for the high-temperature acetylation (90°C), the reagents progressed in a linear manner, consisting of the formation of continuous micropores, from the surface into the interior of the supermolecular structure. In contrast, for the low-temperature acetylation (45°C), the reaction took place only through the segregated micropores on the surface of cellulose. As a result, the successive layers and, subsequently, fragmented platelets of the acetylated surface were solubilized in the reaction medium, and a viscous solution was eventually obtained. The experimental conformity between the SEM and TEM results provided valuable information in support of different solution acetylation mechanisms at low and high temperatures. © 1997 John Wiley & Sons, Inc. J. Appl Polym Sci 64: 1953–1960, 1997     

Synthesis and characterization of the novel cellulose derivative dansyl cellulose

Summary Novel, soluble 5-dimethylamino-1-naphthalenesulfonyl esters of cellulose (2) with a degree of substitution from 0.67 to 1.59 were prepared by esterification of cellulose dissolved in N,N-dimethylacetamide/LiCl solvent system and characterized by means of FTIR-as well as ¹H and ¹³C NMR-spectroscopy. The remaining OH groups of 2 can be fully acetylated in pyridine using N,N-dimethylaminopyridine as a catalyst. The polymers show typical fluorescence and absorption spectra with absorptions at 217, 250 and 317 nm which are in good agreement with quantum chemical calculations.     

Tensile deformation of regenerated and native cellulose fibres

The tensile deformation of well-oriented cellulose fibres has been reexamined. It is demonstrated that not only the fibre structure but also the deformation mechanism is similar to that found in high performance aramid fibres. An explanation is proposed for the difference between the elastic moduli of cellulose I and II. In view of these results it is possible to assess the prospect for improving the mechanical properties of cellulose fibres.     

Calculation of crystallite modulus of native cellulose

Summary A crystallite modulus of native cellulose along the chain axis has been calculated based on the X-ray analysed molecular conformation and the force constants used in the vibrational analysis. The calculated values are 172.9 GPa and 70.8 GPa for the cases with and without the intramolecular hydrogen bondings taken into account, respectively. The intramolecular hydrogen bondings have been found to play an important role on the determination of crystallite modulus and the chain deformation mechanism, based on the calculation of the strain energy distribution to the internal coordinates such as bond lengths, bond angles, and so on.     

Thermal decomposition products of cellulose

Untreated and flame-retardant-treated cellulose were thermally decomposed under vacuum and the products were quantitatively analyzed by gas chromatography. An unidentified product at a retention index of 2270 (between 5-methylfurfural and 5-hydroxymethylfurfural), α- and β-D -glucose, and a group of “dimers” that have not been reported previously were found in this study. The identification of this unknown product should assist in studies on the thermal decomposition of cellulose and further the understanding of the mechanism of flame retardancy.     

Electrospinning of native cellulose from nonvolatile solvent system

Improving and understanding the electrospinnability of native cellulose in room temperature ionic liquids (RTIL) have been a hot issue in recent years. In this study, the electrospinning of cellulose in a highly efficient RTIL of 1-allyl-3-methylimidazolium chloride (AMIMCl) was investigated. The introduction of co-solvent dimethyl sulfoxide (DMSO), which significantly decreased the surface tension, viscosity and entanglement density of the network and increased the conductivity of the spinning dope, contributed to a continuous jet. The problems lying in nonvolatility and the high ionic strength of the RTIL, which unavoidably led to the standing up vertically, adhesion and contractions of the wet fibers during the electrospinning process, were successfully resolved using a rotating copper-wire drum as a collector and solidifying the jet under high relative humidity. The water vapor played an important role in leading to “skin formation” which helped to stabilize the fibrous morphology, and finally smooth ultra-thin regenerated cellulose fibers were obtained. The combination of solvent system and collecting apparatus and conditions provided not only an effective method of producing ultra-thin native cellulose fibers on a large scale, but also a fundamental solution to other electrospinning systems with high ionic strength and nonvolatility. Measurements on WAXD and FT-Raman indicated that the electrospun cellulose fibers were almost amorphous with a little crystallization presented the polymorph of Type-II, which was totally different from the native cellulose with the dominated polymorph of Type-I.     

纳米纤维素的制备与表征

以微晶纤维素为原料,通过硫酸酸解制备获得了纳米纤维素。实验优选获得了酸解制备纳米纤维素的优化条件为:硫酸初始浓度35%,反应温度40℃,酸解时间90 min,此优化条件下,纳米纤维素的产率可达83.55%;SEM和TEM观察产物的形态外貌,确定为纳米级纤维素;XRD分析显示纳米纤维素的结晶度要高于微晶纤维素,而TG分析显示NCC的热稳定性要低于微晶纤维素。     

纳米纤维素的制备与表征

以微晶纤维素为原料,通过硫酸酸解制备获得了纳米纤维素。实验优选获得了酸解制备纳米纤维素的优化条件为:硫酸初始浓度35%,反应温度40℃,酸解时间90 min,此优化条件下,纳米纤维素的产率可达83.55%;SEM和TEM观察产物的形态外貌,确定为纳米级纤维素;XRD分析显示纳米纤维素的结晶度要高于微晶纤维素,而TG分析显示NCC的热稳定性要低于微晶纤维素。     

Properties of bacterial cellulose produced in grape medium by native isolate Gluconacetobacter sp

During the production of grape wine, the occurrence of thick leathery pellicle at the air‐liquid interface was found as a contaminant. The pellicle produced was investigated with a view to use as biodegradable polymer. The bacterium that is responsible for the pellicle production was isolated, characterized and identified as Gluconacetobacter sp. Pellicle was produced in pasteurized grape extract as well as in HS medium by the isolated organism in static conditions. The purified film was subjected for Fourier transform infrared spectroscopy and C¹³ solid NMR spectroscopy analysis, which confirmed the pellicle to be a cellulosic material. Scanning Electron Micrograph showed ultra fine network structure along with cells. The films were tested for its physicomechanical characters, barrier and thermal properties. The films of 25‐μ thickness showed very high tensile strength (41.158 MPa) and elongation of 0.987 mm. The thermal properties of the films were characterized by Differential scanning calorimetry and Thermo gravimetric analysis. The melt peak temperature was found to be 111.65°C. The percentage of weight loss was found to be 20% at 327.86°C. Barrier properties (oxygen transmission rate and water vapor transmission rate), indicated a high oxygen barrier but low water barrier. This is the first report on the barrier properties of bacterial cellulose from Gluconacetobacter sp. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

An electron diffraction study of the crystal structure of native cellulose

The crystal lattice of native cellulose from four sources has been investigated by electron diffraction techniques. The four sources were: cotton, ramie, a bacterial cellulose (Acetobacter xylinum), and an algal cellulose (Valonia ventricosa). Evidence for the existence of at least two different unit cells is provided. There were no systematic absences of odd-order OkO reflections in any of the cellulose patterns, therefore, it was concluded that neither cellulose cell falls into the P2₁ space group.     

Liquid-phase acetylation of tetralin with acetyl chloride over zeolites: inhibition of the reaction by the products

HY and H-beta zeolites are efficient catalysts in the acetylation reaction of tetralin with acetyl chloride. Their activity depends largely on the experimental conditions and is restricted by the strong adsorption of organic species, either acetic acid or acetyltetralin formed in the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

高浓度纤维素的离子液体溶液中均相乙酰化反应(英文)

At relatively high cellulose mass concentrations (8%, 10%, and 12%), homogeneous acetylation of cellulose was carried out in an ionic liquid, 1-allyl-3-methylimidazolium chloride (AmimCl). Without using any catalyst, cellulose acetates (CAs) with the degree of substitution (DS) in a range from 0.4 to 3.0 were synthesized in one-step. The effects of reaction time, temperature and molar ratio of acetic anhydride/anhydroglucose unit (AGU) in cellulose on DS value of CAs were investigated. The synthesized CAs were characterized by means of FT-IR, NMR, and solubility, mechanical and thermal tests. After the acetylation, the used ionic liquid AmimCl was easily recycled and reused. This study shows the potential of the homogeneous acetylation of cellulose at relatively high concentrations in ionic liquids in future industrial applications.     

细菌纤维素膜的合成及表征

以海南椰子水为主要培养体系,实验室自行筛选的木醋杆菌(Acetobacter xylinum)为菌种,采用静态培养方法制备了细菌纤维素（BC）。对该BC和商业BC的结构和性能进行了测试对比,观察BC的微结构特点。结果表明: 制备的BC和商业BC在结构和一些性能方面是相似的,都是无色透明膜,呈三维网状结构和孔洞结构,具有良好的纳米纤维网络特征, 具有良好的吸湿性和极佳的持水能力,本实验制备的BC生产成本低,可根据需要大量制备,在生物医学领域具有良好的、广泛的应用前景。     

低取代羟丙基纤维素的溶解性及其表征方法

采用偏光显微镜、旋转黏度计和广角X射线衍射仪表征了低取代羟丙基纤维素(HPC)在氢氧化钠水溶液中的溶解性能。结果表明:在质量分数为8%的NaOH溶液中,-5℃下可以较好地溶解HPC,高相对分子质量HPC溶解性较差,而低相对分子质量HPC溶解性较好,且动力黏度小;彩色偏光显微照片中紫红色背景区域意味着HPC大分子链呈胶束状溶解分散状态(即尚未充分溶解),充分溶解的HPC溶液则呈现淡蓝色的背景颜色,而未溶解且保持纤维状的HPC则可能呈现红、黄和蓝三色;偏光显微镜法和旋转黏度计法可以用来表征HPC的溶解性,X射线衍射法则不适宜表征其溶解性。     

Surface characterization of cellulose acetate propionate by inverse gas chromatography

The purpose of this paper is to study the surface energetics of the polymer excipient cellulose acetate propionate (CAP) in the solid form. The net retention volumes, V _N, for n-alkanes and polar solutes have been measured in the temperature range 353.15–403.15 K by inverse gas chromatography. The dispersive surface free energy, $ \gamma_{\text{S}}^{\text{d}} $ , and Lewis acid–base parameters $ K_{\text{a}} $ and $ K_{\text{b}} $ , have been determined using V _N values. The $ \gamma_{\text{S}}^{\text{d}} $ values are decreased linearly with increase of temperature. The $ \gamma_{\text{S}}^{\text{d}} $ value at 353.15 K is 24.50 ± 1.54 mJ/m², and the temperature gradient was found to be ?0.287 mJ/m²/K¹. The $ K_{\text{a}} $ and $ K_{\text{b}} $ values are 0.410 ± 0.021 and 1.708 ± 0.388, respectively, which suggest that the CAP solid surface contain relatively more basic sites. The K _a and K _b values of CAP are compared with the similar values obtained on the cellulose acetate butyrate solid surface.     

Application of the turbidimetric titration method to study the molecular-weight distribution of sulfite cellulose in acetylation

Conclusions -- It is recommended to the central plant laboratories of man-made fibres to use the method of turbidimetric titration to determine the molecular-weight distribution of sulfite cellulose in the process of working it up.-- A rapid method has been developed for determining a molecular-weight distribution of sulfite cellulose for acetylation using a selective solvent—precipitant system.Translated from Khimicheskie Volokna, No. 6, pp. 36–38, November–December, 1990.     

Fine structural changes in native and mercerized fibrous cellulose brought about by ethylenediamine and methyl alcohol

X-Ray diffraction (XRD) studies were made on native as well as mercerized ramie and cotton fibers after swelling them in ethylenediamine (EDA) solutions and washing out the swelling agent using methyl alcohol (MeOH). These treatments are shown to convert the cellulose I and II lattices into cellulose III_I and III_II type lattices, respectively. Treatment of the III_I and III_II samples in boiling water or hydrochloric acid results in reconversions of their crystal lattices into the respective parent types. Alkali treatment causes a III → II type conversion. Studies using alkali-swollen fibers as well as fibers of different lateral order as starting materials indicate the importance of the structural organization in the cellulosic materials in the production of the cellulose III lattices. Possible mechanisms involved in the lattice transformations in cellulose brought about by the EDA and MeOH treatments are discussed.