Depolymerization of cellulose

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... 

Macrocellulosic radicals initiated by ionizing radiation can be divided into two classes one class in which the radiant energy is selectively absorbed by the cellulose molecule and another class in which the radiant energy is randomly absorbed by the cellulose molecule. In both cases, after localization of the absorbed radiant energy, oxidative depolymerization of cellulose is initiated, and macrocellulosic radicals are formed (3). 

Rinaldi R, et al. Which controls the depolymerization of cellulose in ionic liquids the solid acid catalyst or cellulose ChemSusChem. 3(2) 266-76. 

Conditions selected so that the copolymer contained about the same amount of cellulose, 77-82% AN = acrylonitrile DMF = N,N-dimethylformamide. b Initial molecular weight of cellulose 7.1 X 105 for ionizing radiation molecular weight of cellulose was determined at dosage indicated no determination was made on possible oxidative depolymerization of cellulose by chemical redox systems. c Based on poly (acrylonitrile) recovered from acid hydrolysis of copolymer and on intrinsic viscosity method. 

Fig. 8-16. Depolymerization of cellulose (viscosity decrease) during oxygen bleaching of pine kraft pulp. Dotted line, no inhibitor addition full line, inhibitor added (Mg salt).

Schweizer s solution (Cuoxam) [Cu(NH3)4](OH)2 Dark blue. Extensive depolymerization of cellulose in the presence of oxygen. 

Lignin is the second most abundant natural polymer in the biosphere and the most abundant renewable aromatic material. It comprises 15-30% of woody plant cell walls, forming a matrix surrounding the cellulose. This encrusting matrix (1,2) significantly retards the microbial depolymerization of cellulose and thus lignin plays a key role in the earth s carbon cycle (1-3). 

Depolymerization of cellulose fibers during irradiation is accompanied by a reduction in crystallinity, and, at high doses, extensive decomposition occurs. A dose of 5 X 10 equivalent roentgens brings about marked degradation and is sufficient to convert cotton linters into water-soluble materials. After irradiation, cellulose is more susceptible to acid hydrolysis and exhibits an after-effect. When irradiation is terminated, the intrinsic viscosity of cupriethylenediamine solutions of the irradiated cellulose continues to decrease. This behavior is initiated by oxygen and terminated by water. A similar effect is encountered with pectins after irradiation. 

When the pretreatment temperature exceeds 100 C, monophosphates of cellulose are formed, the development of intermolecular cross-linking is promoted and depolymerization of cellulose is hindered. 

This initial oxidative depolymerization of cellulose evidently opens up the wood cell wall structure so that cellulolytic and hemi-cellulolytic enzymes can reach their substrates despite the presence of lignin. Solubility of wood in 1% NaOH increases markedly on brown-rot attack IS) and reflects cellulose depolymerization and the opening up of the wood structure. 

Figure 7. Depolymerization of cellulose in wood by brown-rot fungi might involve Fe and HgOg (92, 96, 97).

Table I. Rate Constants for the Depolymerization of Cellulose in Air and Nitrogen...

It has been suggested that the depolymerization of cellulose to levoglucosan is the first, and rate-determining, step. General mechanisms involved in the pyrolysis of cellulose have been discussed, - and some of these have invoked the formation of 1,2-anhydro-a-D-glucopyranose as an essential intermediate - The effect of the pr ence of salts on this mechanism has also been discussed. " - ... 

Brown The determinations of size of the cell-wall capillaries and the cellulases of fungi indicate that the enzymes that have been isolated to date are so large that they probably can penetrate only a few cell-wall capillaries in wood and cotton. This conclusion is supported by Cowling s DP data for the action of the white-rot fungus, Polyporus versicolor, on wood (Figure 13). But it is also contradicted by the same type of data for the effect of both the brown-rot fungus, Poria monticola, on wood (Figure 13) and of Myrothecium verrucaria on mercerized cotton as shown by Selby (60). Thus we believe that the catalysts responsible for the initial depolymerization of cellulose in wood and cotton by these two... 

Photodegradation including fragmentation of lignin molecules and depolymerization of cellulose... 

Fig. 22. Reductive depolymerization of cellulose derivatives after permethylation.

Demin, V. A., Kabal nova, N. N., Osipova, G. I., and Shereshovetz, V. V., Depolymerization of cellulose upon ozonation, Russ. J. Appl. Chem., 66... 

Increasing the SA concentration to more than 65 wt% led to further diminution in yield, crystallinity, and DP of the regenerated particles. After hydrolysis of the initial sample with 67 wt% SA the yield of the particles was zero because the hydrolyzed and dissolved cellulose cannot be regenerated from the acidic solution by dilution with water. This was caused by the fast acidic depolymerization of cellulose with 67 wt% SA and forming of the water-soluble ohgomers. 

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