Cellulose models

Cellulose Models for Fonnaldehyde Storage in Wood Carbon-13 Nuclear Magnetic Resonance Studies... 

C-NMR spectra of water soluble cellulose model compounds indicate that formaldehyde is capable of reacting with wood cellulose functions under hot press conditions as well as at room temperature yielding hemiacetals. The formation of hemiacetals is reversible, and thus constitutes a reservoir for formaldehyde storage. Due to its affinity for water, formaldehyde released during the manufacture of UF-resin bonded products will be retained in the aqueous phase of wood. Wood contains about 9 wt% of moisture. Most of this is in the S-2 secondary cell walls that consist mainly of wood cel IuIose. 

MEYER ET AL. Cellulose Models for Formaldehyde Storage in Wood... 

Figure 6.60 (c) Reaction of cellulose models with chlorine in acidic aqueous solution. 

DA Blythe, FR Schroeder. Degradation of a Nonreducing Cellulose Model, 1,5-Anhydro-4-O-P-D-Glucopyranosyl-D-Glucitol, under Kraft Pnlping Conditions. J Wood Chem... 

Monsalve et al. [236] studied the degradation of dehydroascorbic acid and chlorogenic acid, at pH 6, and at variable water activities and temperatures in model systems containing cellulose, dehydroascorbic acid and/or chlorogenic acid. They found that at 45°C nonenzymatic browning of dehydroascorbic acid-cellulose model system increased linearly through a certain time and then it... 

Based on the number and location of the maxima and minima in the relationship between the band intensities and the polarization of the incident light relative to the chain axis, the bands in the Raman spectrum of cellulose could be divided into four groups. The about the direction of the vibrational motions in cellulose. The directions of the vibrations are such that the major change in polarizability associated with the motions is either parallel or perpendicular to the chain axis. Raman spectra recorded from deu-terated celluloses allowed the vibrational modes involving C-H and 0-H motions to be identified. These spectra demonstrated that most of the modes are complex coupled vibrations. Normal coordinate analyses of cellulose model compounds were done to determine the types of motion most likely to occur in each region of the spectrum. The calculations also suggested that the vibrational motions are very complex. The information from the normal coordinate calculations. 

In the present study, the role of cellulose physical structure in alkaline reactions was investigated by comparing the alkaline degradation of highly crystalline (cellulose I) fibrous hydrocellulose with that of amorphous (noncrystalline) hydrocellulose. The amorphous substrate was taken as a cellulose model the reactivity of which would most closely approximate that of alkali-soluble cellulose. The availablity of such an approximation to the inherent reactivity of cellulose allowed evaluation of the effects of the more highly ordered structure of the fibrous hydrocellulose. 

Fig. 2 Drainage behavior of cellulosic model suspensions with low or high anionic trash content (TC) in the presence of PDADMAC. (a) Drainage volume Fsr in dependence on the amount of PDADMAC the dotted lines exhibit the point of zero charge in the suspension, (b) Net charge of the residual solution/mixture in dependence on the amount of added PDADMAC...

Konttiui, E Thiine, PC Niemantsverdriet, JWH. Cellulose model surfaees-simplified preparation by spin coating and characterization by X-ray photoeleetron speetroseopy, infrared spectroscopy and atomic force microscopy. Langmuir, 2003, 19, 5735-5741. 

The crystal structure of native ramie cellulose was shown to be similar to that recently reported for Valonia cellulose. The earlier conclusion that the ramie diffraction data could not be satisfied by a conventional cellulose model is refuted. R (an indication of diffraction error) values of 0.158, 0.185, and 0.175 were obtained for anti-parallel, parallel up, and parallel down alignments respectively. The author considers that the anti-parallel model provides the best accounting for the ramie data and is therefore probably the correct model for both cotton and ramie cellulose. The changes in crystallinity and physical characteristics of microcrystalline cellulose which occur on grinding have been studied. Under one set of grinding conditions, the specific surface area rose... 

Investigation of cellulose systems in closer detail requires the choice of representative cellulose model surfaces for the experiment. A spin-coated cellulose surface on mica was the first model surface used in studies of forces in papermaking systems (70). This work was followed by other SFA studies using Langmuir-Blodgett (LB) films of cellulose (11-14). These films are noticeably smoother and more stable than spin-coated surfaces. In studies using the atomic force microscope (AFM) colloidal probe technique (Ducker et al. (75)), interaction forces were measured either between two cellulose beads (16,17) or between cellulose beads and spin-coated cellulose surfaces (18,19). 

This study, and a H NMR study conducted in parallel on single ionic liquids with ethanol as cellulose model, clearly demonstrated that as halide anions exhibit strong and preferential interactions with the H2 of the 1,3-dialkylimidazolium cation rather than with the cellulose (or ethanol) hydroxyl group, the cellulose-dissolving anion... 

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