Cellulose results

Addition of bran from hard red and soft white wheat bran, psyllium fiber, and cellulose resulted in increased losses of calcium in feces in comparison to losses when no fiber supplements were used (P<0.05). Urinary calcium losses were not significantly affected however, calcium balances were lowered when these four fiber sources were added to the laboratory controlled diet (P < 0.05). 

It has been realized for many years that excessive acidity is the single most serious cause of degradative effects on paper (I, 2, 5, 6). Although acids may be present from many sources (carboxyl groups in cellulose resulting from oxidation and the presence of acidic hemicellu-loses, bleach residues, some wet-strength resins, etc.), the most important... 

Physical interactions between drug and excipient also can compromise quality. Adsorption of drug by microcrystalline cellulose resulted in drug dissolution being less than complete. Interaction between chloramphenicol stearate and colloidal silica during grinding led to polymorphic transformation. 

In each case, preconditioned material was placed in the hopper of an instrumented tablet machine and the performance of these two materials was compared at constant machine settings. The sample with 5.1% MC produced tablets that weighed slightly less (an effect on flow and bulk density), and as a result were exposed to lower compression force. However, the moist microcrystalline cellulose resulted in harder tablets, even though it had been exposed to lower compression force. The loci of points on the compression force versus hardness profile (Fig. 20) for the tablets indicate a different fundamental behavior for the two materials. 

As shown in the model, pyrolysis of cellulose results in solid, liquid and gaseous products. However, the proportions of the product yields can change depending on the process conditions. The knowledge of thermodynamics and kinetics of the reaction pathways allows us to adjust the conditions to maximize the yield of the desired products. 

Nitric Acid and Nitrate Activation. The reactions of HNO3, nitrates, and nitrogen oxides with lignocellulosic materials have been a subject of numerous publications. The specific transformations can be subdivided into acid reactions, oxidation reactions, and nitration-esterification reactions. With HNO3 and more acidic salts the acid reactions predominate at higher dilutions, and parallel those of aqueous solutions of H2SO4 and other similar acids. Oxidation of cellulose results primarily in oxidation of primary hydroxyls to carboxyls, with the secondary hydroxyls oxidized less. Nitration leads... 

This reaction is supposed to have an E2 mechanism [32]. Further decomposition of the dehydrated cellulose results in an increased yield of water, char, gases and carbonyl compounds and a simultaneous decrease in levoglucosan formation as compared to pure cellulose pyrolysis. 

A.L. Margolin, Photochemistry of cellulose. Results of science and engineering. Chemistry and technology of highmolecular compounds, volume 24, 84-158, Moscow (1988) (in Russian). 

In this Section will be considered a proposal that polymorphism of chitins and cellulose results from differences in chain folding. To illustrate this hypothesis, RudalF used the two polymorphs of chitin, which he referred... 

The general pyrolysis mechanisms of polysaccharides have been determined from model studies on cellulose and involve the splitting of the polysaccharide structure by three basic chemical reaction mechanisms dehydration, retroaldolization, and decarboxylation. Using these basic pyrolysis mechanisms, it is possible to explain the pyrolysis of polysaccharides and evolved pyrolysis products. The hexose degradation pathway for cellulose results in formation of furan- and pyran-type fragments and smaller acyclic aldehyde and ketone fragments. ... 

Fig. 4 Time course of ethanol, glucose, xylose and cellobiose concentrations during SSF of wet-exploded wheat straw at 14% DM and enzyme loading of 10 FPU/g-cellulose. Results are average of duplicates...

Cellulose, the most abundant organic compound found in nature, forms the principal constituent of cell walls in higher plants. It accounts for 91% of cotton fibers and 40-50 of wood. It is a linear chain made of up to 10 (l->4)-linked P-D-glucose molecules. The characteristics of cellulose result from the tendency of the individual chains to form linear, extended ribbons, which assemble to form highly ordered, hydrogen-bonded microfibrils. If the ribbons are laid down in sheets in a parallel manner such that all reducing terminals occur at the same side of the bundle, it is called cellulose I. This is the most common natural material (Fig. 4.2.23). 

Degradation of oat and barley glucans with Streptomyces cellulase, which produces mainly cellobiose and cellotriose from cellulose, resulted in production of a trisaccharide fraction and a tetrasaccharide fraction as the major products. These were isolated by preparative paper-chromatography, and the trisaccharide was found to preponderate ... 

Cellulose Crystallization. For crystallization below 100 C, the solutions were poured into petri dishes and positioned inside a closed vessel containing an excess of water. The vessel was then fitted into a temperature controlled oil bath and brought to the crystallization temperature. Crystallization of cellulose resulted from the diffusion of water into the solution. Crystallization was complete within a few minutes at 90 C whereas several days were necessary at room temperature. For crystallization between 100 C and 120 C, a similar principle was used except that a thick-wall sealed glass vessel was used to prevent water vapor from escaping. 

In 1920, the Tubize Company built a plant to produce the yarn in the United States. By 1934, however, other types of superior rayon had been developed, so the nitrocellulose plant was sold to a company in Brazil. Several incidents of explosions and fires caused by the incompletely denitrated cellulose resulted in setbacks to the Chardonnet silk process, but, fortunately, the simultaneous development of cuprammonium and viscose solutions for spinning rayon rapidly replaced the more dangerous nitrocellulose fibers. 

Explain why oxidation of cellulose results in cellulose with a high copper number but alkaline oxidation gives cellulose with high acid group content but low copper numbers. 

The major advantage of using cadoxen solutions of cellulose for SEC is that the cellulose need not be derivatized before determination of the SEC. This eliminates the time-consuming step of derivative formation, which in the case of the tricarbanilate derivative requires more than 48 h. In addition, smaller cellulose samples are required and any changes in the cellulose resulting from sample preparation are minimized. 

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