Electron spectroscopy cellulose

Fomier de Violet, P., Nourmamode, A., Colombo, N., and Castellan, A., "Study of Brightness Reversion of Bleached Chemithermomechanical Pulp by Solid State Electronic Spectroscopy", Cellulose Chem. Technol., 1989, 23, 535. 

By using this technique acrylamide, acrylonitrile, and methyl acrylate were grafted onto cellulose [20]. In this case, oxidative depolymerization of cellulose also occurs and could yield short-lived intermediates [21]. They [21] reported an electron spin resonance spectroscopy study of the affects of different parameters on the rates of formation and decay of free radicals in microcrystalline cellulose and in purified fibrous cotton cellulose. From the results they obtained, they suggested that ceric ions form a chelate with the cellulose molecule, possibly, through the C2 and C3 hydroxyls of the anhy-droglucose unit. Transfer of electrons from the cellulose molecule to Ce(IV) would follow, leading to its reduction... 

Graft and block copolymers of cotton cellulose, in fiber, yam, and fabric forms, were prepared by free-radical initiated copolymerization reactions of vinyl monomers with cellulose. The properties of the fibrous cellulose-polyvinyl copolymers were evaluated by solubility, ESR, and infrared spectroscopy, light, electron, and scanning electron microscopy, fractional separation, thermal analysis, and physical properties, including textile properties. Generally, the textile properties of the fibrous copolymers were improved as compared with the properties of cotton products. 

The primary sources of information concerning the molecular structure of cellulose have been x-ray and electron diffractometric studies, conformational analyses, and vibrational spectroscopy. The work up to 1971 was very ably reviewed by Jones (10), and by T0nnesen and Ellefsen (II, 12). They generally concluded that although much evidence can be interpreted in terms of cellulose chains possessing a two-fold axis of symmetry, in both Celluloses I and II, none of the structures proposed... 

Samples (10 mL) of humic acid in the appropriate buffer (y - 0.05-0.1), typically containing between 0.1 and 2.0 grams of humic acid per litre (determined by electronic absorption spectroscopy), were placed in regenerated cellulose dialysis bags. The closed bags were placed in 100 mL bottles, previously filled with 40 mL of the buffer containing varying concentrations (10 7 - IO m)... 

Now that the range of likely shapes has been defined by experiments on related molecules and by energy calculations, we focus on the details of specific structures that have been observed for real, crystalline cellulose molecules, primarily by x-ray, neutron, and electron diffraction studies. A number of landmark concepts have been established with electron microscopy, as well. Infrared (IR), Raman, and nuclear magnetic resonance (NMR) spectroscopy have all also been important in the quest for understanding cellulose structure. Such data, while so far not able to provide complete definitive structures themselves, constitutes additional criteria that any proposed structure must be able to explain. In addition, unlike crystallography, the resolution of spectroscopic methods is not directly affected by the dimensions of the... 

Gel-permeation chromatography" is used to compare the pore structure of jute, scoured jute and purified cotton cellulose. Both native and scoured jute have shown greater pore volumes than cotton. The effects of alkali and acid treatment on the mechanical properties of coir fibers are reported." Scanning electron micrographs of the fractured surfaces of the fibers have revealed extensive fibrillation. Tenacity and extension-at-break decrease with chemical treatment and ultraviolet radiation, whereas an increase in initial modulus and crystallinity is observed with alkali treatment. FTIR spectroscopy shows that the major structural changes that occur when coir fibers are heated isothermally in an air oven (at 100, 150 and 200 °C for 1 h) are attributable to oxidation, dehydration and depolymerization of the cellulose component. 

The CNTs, both single-walled nanotubes (SWNT) and multi-walled nanotubes (MWNT) prepared by chemical vapor deposition (CVD) and arc-discharge (AD) methods, respectively, were purchased from Iljin Nanotech, Co., Korea. For proton and electron irradiation experiments, CNTs sheets were prepared as shown in Figure 2 by filtration of the CNT solution mixed in dimethylformamide through a cellulose membrane (pore size 0.45 pm). The thickness of the CNT sheets was approximately 0.5 mm, and they were 47 mm in diameter. After drying in a vacuum oven at 80 °C for 24 hours, CNT sheets (Figure 2) were obtained. These sheets were used in the radiation experiments, and were used for analysis such as SEM, Raman spectroscopy and XPS without any further treatment. For a dispersion test, a CNT powder was used instead of the CNT sheets. 

With the wide acceptance of the proposal of the two crystalline forms (I and I/3) came the challenge of understanding the differences between them and their relationship to each other within the morphology of native cellulosic tissues. A number of complementary approaches were pursued by different investigators in the search for answers. Some were based on further application of solid-state C NMR to the study of different celluloses as well as to celluloses that had been subjected to different modifying treatments. Others were based on the application of Raman and infrared spectroscopy to new classes of cellulosic samples. Others were still based on the refinement of electron microscopic and diffractometric methods. The results of these investigations will be presented in summary. 

P-Mannan is water-insoluble and solubilizing it requires very strong alkali, cuprammonium or derivatization. X-ray and electron diffraction show that mannan has a ribbon-like conformation, similar to cellulose, with the 2-OH axial instead of equatorial. In seeds (palm, coffee, caraway) a few (<5%) of a-Gal groups are attached to the hydroxymethyl and in seaweeds a small percentage (<5) of Glc residues may occur in the chain. A pure P(l-4) mannan has been extracted from cell walls of the siphonous green alga Codium latum as the methylol mannan with paraformaldehyde dimethylsulphoxide. It was purified by size exclusion chromatography in dimethyl sulphoxide and recovered by the addition of water or methanol and could be re-dissolved in hot dimethyl sulphoxide. Infra-red and n.m.r. spectroscopy and periodate oxidation confirmed the unbranched P(l-4) structure [185]. 

Chemically modified celluloses have been analyzed by conventional wet methods and by various Instrumental methods designed to differentiate bulk and surface properties. Electron emission spectroscopy for chemical analyses (ESCA) used alone and In combination with radiofrequency cold plasmas yielded elemental analyses, oxidative states of the element, and distribution of the element. Techniques of electron paramagnetic resonance (EPR), chemiluminescence, reflectance infrared spectroscopy, electron microscopy, and energy dispersive X-ray analyses were also used to detect species on surfaces and to obtain depth profiles of a given reagent in chemically modified cottons. 

Cellulose, which Is one of the most abundant organic substances found In nature, has been extensively studied by various techniques such as x-ray scattering, electron microscopy, IR and Raman spectroscopy, NMR spectroscopy etc. However, the crystal structure and noncrystalline state are not yet solved for cotton, ramie, bacterial and valonla celluloses which can be easily obtained in pure form. Cross-polarization/magic angle spinning(CP/MAS) C NMR spectroscopy is a promising new method to study these unsolved problems of cellulose, because this method is very sensitive to local molecular conformations and dynamics. 

The supermolecular structures of cellulose have been investigated extensively by many techniques including x-ray and electron diffrac-tometry, electron microscopy, IR and Raman spectroscopy, broad-line proton NHR and solid-state c-uuR. Nevertheless, many questions remain concerning the solid-state structures. 

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