Nanocomposite materials from latex and cellulose whiskers

Composite materials were processed by casting a mixture of aqueous suspensions of latex and microfibrils. These microfibrils, or whiskers, are extracted from a sea animal and are monocrystals of cellulose, with an aspect ratio around 100 and an average diameter of 20 nm. It has been found that the mechanical properties (shear modulus) are increased by more than two orders of magnitude in the rubbery state of the polymeric matrix, when the whisker content was 6% (w/w). This very large effect is discussed on the basis of different types of mechanical models and it is concluded that these whiskers form a rigid network, probably linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.     

Effect of cellulase on the pore structure of bead cellulose

An enzymatic treatment with cellulases fromTrichoderma viride was investigated in its effect on the pore structure of different types of bead cellulose. One objective of this study was to establish a suitable procedure for combined enzymatic treatment and solvent exchange that would restore the original pore structure which the beads had before drying without causing major losses in mechanical stability. Another aim was to further increase the accessible pore space and internal surface area for separation of large molecular weight compounds with regard to Chromatographic applications. Finally, an attempt was made to extend the findings for unsubstituted beads to the derivatives carboxymethyl (CM) and diethylaminoethyl (DEAE) cellulose beads. The enzymatically treated samples were characterized by microscopic methods and porosity measurements such as mercury porosimetry, nitrogen sorption and size exclusion chromatography. It was found that under controlled conditions the low-porosity surface layer of dried beads could be removed making the internal pore space accessible without reducing the resistance to deformation of the beads. Additionally, a shift in pore size distribution towards larger pores was observed. Supplementary swelling treatments in solvents of high swelling power could substantially restore the former porosity of the dried beads but did not enhance the accessibility to the cellulases to a considerable extent. Internal pore volume and surface area of the derivatives were dramatically increased in the case of DEAE upon enzymatic hydrolysis, however, at the expense of mechanical stability, whereas CM was found to be less affected.     

非共价键自组装有机功能材料

分子自组装对于某些化学反应过程、生物化学过程及生命活动的模拟等方面具有重要的意义。本文对非共价键组装方式自组装的有机功能材料的分类，结构、性质、自组装机理以及研究进展进行了综述。     

Hydrogen bonds in regioselectively substituted cellulose derivatives

Formation of hydrogen bonds in various cellulose derivatives, 2,3-di-O- and 6-O-substituted cellulose ethers, were characterized by FTIR and solid-state CP/MAS¹³C-NMR. The polymers were synthesized by regioselective substitution of hydroxyl groups and had a uniform structure. Since their three hydroxyl groups (OH) are selectively blocked, the cellulose derivatives appeared to form specific inter- and intramolecular hydrogen bonds. The characteristic OH stretching frequencies in IR spectra and the C-1 chemical shift in CP/MAS spectra of 6-O-substituted cellulose derivatives indicated existence of two equivalent intramolecular hydrogen bonds between ether oxygen and OH groups at 3-OH-O5′ and O6-HO-2′ [Figure 3(C)]. Influence of the substituents at the C-6 position on the formation was not significant except trityl group. Behavior of the hydrogen bonds in 6-O-tritylcellulose were also discussed. © 1994 John Wiley & Sons, Inc.     

Surface characterization of TEMPO‐oxidized bacterial cellulose

In this study, we focused on the surface character of bacterial cellulose (BC) before and after oxidation mediated by 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO).Solid‐state ¹³C NMR, XPS, SEM, contact angle and surface free energy analyses were performed to investigate the effects of various parameters (reaction time and oxidant and catalyst concentrations) on the surface composition, morphology and polarity of the BC. The results provided by the combined use of these techniques showed that hydrogen bonds were disrupted on the BC surface after carboxylation occurred; therefore, the surface of oxidized BC was rougher than that of the original BC, and the surface free energy, especially the polar components, increased after oxidation. Copyright © 2013 John Wiley & Sons, Ltd.     

基于非共价键的本征型自修复聚合物材料及其应用

自修复材料作为一种拥有结构上自愈合能力的智能材料近年来得到了快速发展。具备自修复性能的聚合物材料主要包括外援型和本征型。由于本征型自修复聚合物材料具有潜在的自修复能力,且能实现多次修复,所以该领域对于本征型自修复聚合物材料的关注越来越多。由氢键、π-π堆积、疏水作用、离子作用和主客体作用等非共价键力形成的本征型自修复聚合物体系不需要或需要极少外界能量就能实现快速、高效修复。这将是实现节约能源,社会可持续发展的重要途径。本文以不同类型的非共价键为线索,综述了近年来基于非共价键的本征型自修复聚合物材料的发展及其应用,并展望了其未来的发展方向。     

Quantification of cellulose forms in complex cellulose materials: a chemometric model

In this paper, we present a chemometric model for quantifying the cellulose forms with different states of order found within cellulose I fibrils. The relative amounts of the different cellulose forms, that is crystalline cellulose I, para-crystalline cellulose and cellulose at accessible and inaccessible cellulose surfaces, were determined by non-linear least squares fitting of the C4-region in CP/MAS ¹³C-NMR (Cross-Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance) spectra. By correlating these results from the C4-region with the full spectral data we obtained a model which is able to provide an assessment of the relative amounts of the different cellulose forms directly from NMR-spectra of complex lignocellulosic samples. Furthermore, this model enabled new assignments to be made in the C1-region for signals from cellulose at accessible fibril surfaces.     

The relationship between intramolecular hydrogen bonds and certain physical properties of regioselectively substituted cellulose derivatives

This article tries to provide some direct evidence about the relationship between the intramolecular hydrogen bonds in cellulose and their corresponding effect on physical properties. The formation of intramolecular hydrogen bonds has been proved to contribute directly to certain physical properties of cellulose, such as its solubility in solvents having different polarities, the relative reactivities of the hydroxyls in a repeating unit and its crystallinity, using a 6-O-methylcellulose (6MC) film that was known¹ to have intramolecular hydrogen bonds. The excellent solubility of 6MC when compared with other cellulose derivatives indicated a lack of interchain hydrogen bonds. A comparison of the relative reactivities between the C-2 and C-3 position hydroxyls in 6MC also indicates that intramolecular hydrogen bonds once formed in 6MC films are possibly maintained even after dissolution in solvents. In addition, the poor crystallinity exhibited by 6MC supports the idea that crystallization in cellulosics may be dependent more upon preferencial interchain hydrogen bonding at the C-6 position hydroxyls than upon a uniform structure such as that found in 6MC, where every structural unit is completely and regioselectively substituted, distinguishing it from other synthetic polymers such as polyolefins and polyesters. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 717–723, 1997     

键合型邻乙酰水杨酸纤维素酯手性固定相的合成及应用

将邻乙酰水杨酸纤维素酯通过间隔臂--2-（3,4-环氧环己基）乙基三甲氧基硅烷键合于硅胶之上,制得键合型手性固定相CSP1,考察了其与同类纤维素衍生物制得的涂敷型手性固定相在拆分效果方面的异同,并探讨了其差异的原因与机理。为了印证间隔臂中环己基对于手性拆分的作用,本文又将CSP1与间隔臂中不具有环己基的键合型手性固定相CSP2进行了拆分对比,进一步证实了间隔臂中环己基的作用。结果表明,键合型手性固定相相比涂敷型固定相在拆分咪唑类药物方面具有优势,这种优势一方面来自于流动相范围的扩大,另一方面是由于间隔臂中环己基对纤维素表面结构的修饰作用。     

Incorporation of quadruply-bonded units into solid-state materials

The thirtieth anniversary of the quadruple bond marks a time in science when synthetic inorganic chemists are exploring molecular routes to new solid-state materials. Dinuclear transition metal complexes possessing , , and components to their M-M bonding present exciting opportunities for the design of macromolecular compounds with interesting optical, electronic, and magnetic properties. This brief review reports recent progress in the area of ordered molecular arrays incorporating quadruply bonded and other multiply bonded M₂ units.     

Reactivities of cellulases from fungi towards ribbon-type bacterial cellulose and band-shaped bacterial cellulose

We have investigated the reactivities of various cellulases onribbon-type bacterial cellulose (BC I) and band-shaped bacterial cellulose (BCII) so as to clarify the properties of different cellulases. BC I waseffectively hydrolyzed by exo-type cellulases from different fungi from twicetofour times as much as BC II, but endo-type cellulases showed little differencein reactivity on those substrates. One of the endo-type cellulases, EG II fromTrichoderma reesei, degraded BC II more rapidly thanexo-type cellulases even in the production of reducing sugars. The degree ofpolymerization (DP) of BC II was rapidly decreased by endo-type cellulases atanearly stage, while exo-type cellulases did not cause the decrease of DP atthe initial stage, though the decrease of DP was observed after an incubation of24 h. All exo-type cellulases adsorbed on BC I and BC II,whileendo-type cellulases except for EG II adsorbed slightly on both substrates. Itwas interesting to observe EG II adsorbed on BC I but not on BC II. It issuggested that the adsorption of enzyme on cellulose is important for thedegradation of BC I, but not for BC II. It is proposed that the ratio of aspecific activity of each enzyme between BC I and BC II represents thedifference in the mode of action of cellulase. Furthermore, the K _RW value, which we can calculate from thedecrease of DP/reducing sugar produced, is effective for discriminating themode of action of cellulase, especially the evaluation of randomness in thehydrolysis of cellulose by endo- and exo-type cellulases.     

New waterborne epoxy coatings based on cellulose nanofillers

New nanocomposites based on a waterborne epoxy emulsion and a suspension of cellulose crystallites were prepared by film casting in order to obtain coatings displaying both flexibility and stiffness. Tunicin cellulose whiskers are attractive reinforcing fillers due to their high aspect ratio, large interface area, and, significant mechanical properties). Typical processing problems for this type of composite are related to high viscosity values of filled polymers in the in the molten state, the incompatibility between hydrophobic matrices and hydrophilic cellulose and the formation of hydrogen bonds between cellulose of this type of natural fibres in an epoxy matrix. The aim of this work is to solve some of the problems above mentioned by selecting the nature of the components used for coating synthesis film processing. The dynamic mechanical properties display an important improvement of the composite modulus in the rubbery state of the matrix at low concentrations of fillers, which can not be expected other cellulose based fibers.     

Characterization of magnetic membranes based on bacterial and man-made cellulose

Ferrites were synthetized in situ in two different neutral cellulose gels: a never-dried bacterial cellulose membrane and a never-dried cast film using N-methylmorpholine-N-oxide as solvent. X-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometry (VSM) and Mossbauer spectroscopy were used to characterize the resulting magnetic nanocomposites. TEM micrographs showed the presence of ferrites in two different shapes, acicular and equiaxial, respectively hydrated ferric oxides (FeOOH) and the spinel oxides: maghemite (gamma-Fe2O3) or magnetite (Fe3O4). Thin sections of bacterial cellulose showed these particles to be located along the cellulose microfibrils, which are assumed to provide a site for their nucleation. Room temperature magnetization curves showed all samples to be superparamagnetic     

分子间的非共价相互作用：σ-穴键和π-穴键

第四到第七主族元素以及惰性气体元素可以作为电子受体位点形成分子间吸引性的非共价键合作用。这些电子受体位点,即缺电子密度的位点,大多情况下具有正的分子表面静电势,可以将其分为2类。沿着σ共价键键轴延伸方向原子的外围中心具有正的分子表面静电势的区域称之为σ-穴。而垂直于分子σ-骨架平面具有正的分子表面静电势区域称之为π-穴。σ-穴和π-穴与富电性位点之间吸引性的相互作用分别称之为σ-穴键和π-穴键。σ-穴键倾向于180°,而π-穴键倾向于90°。按照元素周期表族的名称,σ-穴键又分为碳素键、氮素键、氧素键、卤键、惰素键等。可见流行的卤键只是σ-穴键的一个子集。π-穴键分类显得复杂些,可简单分为单原子和多原子π-穴键。     

Synthesis,crystal structure,photoluminescence properties of organic-inorganic hybrid materials based on ethylenediamine bromide

In this work, a new orthorhombic organic-inorganic hybrid single crystal (C₂H₁₀N₂)₂MnBr₄.2Br with-Zero-dimensional structure was synthesized by slow evaporation method at 75 °C. The crystal structure and intermolecular interactions were performed by single crystal X-ray diffraction and Hirshfeld surface. Optical properties of (C₂H₁₀N₂)₂MnBr₄.2Br were systematically studied by Raman, infrared spectrum, UV–vis, photoexcitation spectra, and photoluminescence spectra. The optical band gap (E_g = 2.61 eV) were calculated from the absorption spectra of (C₂H₁₀N₂)₂MnBr₄.2Br. This hybrid materials also had shown good thermal stability (decomposition temperature: 288–660 °C). Finally, photoluminescence measurements showed a strong excitation line at 362 nm and a strong fluorescence at 537 nm which makes it a promising material in luminescence field.     

Surface modification of natural cellulose substances:toward functional materials and applications

Combining various synthetic chemical processes and biological assemblies provides a promising strategy for the design and fabrication of functional materials with tailored structures and properties.The unique multilevel structures and morphologies of natural cellulose substances such as ordinary commercial laboratory filter paper make them ideal platforms for the self-assemblies of various functional guest molecules that are to be deposited on the surfaces of their fine structures,and the resulting composite matters show significant potentials for various applications.The surface sol-gel process was employed to deposit ultrathin metal-oxide(e.g.,titania and zirconia)gel films to coat the cellulose nanofibers in bulk filter papers;thereafter,monolayers of specific guest substrates were immobilized onto the surfaces of the metal-oxide gel films.Highly selective,sensitive,and reversible chemosensors based on the surface modification of filter paper were obtained toward the fluorescence and colorimetric detection of various analytes such as heavy-metal ions,inorganic anions,amino acids,and gases.Cellulosebased composite materials with superhydrophobic,antibacterial,or luminescent properties were fabricated by self-assembly approaches toward practical applications.     

关于键解离能、键能、反应焓变的探讨

键解离能、键能、反应焓变是广泛应用的化学术语,也是中学化学教学中容易混淆的概念。通过探讨3者的联系及区别,以期让教师形成清晰认识,从而在教学实践中加以准确应用。     

基于认知结构测查的化学概念学习评价——以“化学键”为例

通过流程图法对高中生“化学键”认知结构测查的结果表明：在“化学键”概念的学习过程中,多数学生在建构知识的过程中注重对概念文字表述的记忆,而欠缺对相关概念内涵的深层次理解,尤其对“化学键”相关概念中所蕴含的化学学科观念较为忽视,认知困难主要表现在“离子键与共价键的本质”“离子键的形成过程”等内容中。     

Magneto-responsive hybrid materials based on cellulose nanocrystals

We fabricated self-standing films of cellulose nanocrystals (CNC) and electrospun composite fibers with CNC and polyvinyl alcohol both with magnetic properties arising from cobalt iron oxide nanoparticles in the CNC matrix. Aqueous dispersions of cobalt-iron oxide nanoparticles (10–80 nm diameter) and CNCs (ca. 150 nm length) were used as precursor systems for the films and composite fibers. The properties of the hybrid material were determined by electron and atomic force microscopy, X-ray diffraction, thermogravimetry and magnetometry. The CNC-inorganic system was ferromagnetic, with a saturation magnetization of ca. 20 emu g^?1 of the magnetic phase. We demonstrate potential applications of the precursor dispersions, including magnetic fluid hyperthermia and highlight possible uses of the CNC-based magneto-responsive systems in biomedical and magneto-optical components.