Cellulose amorphous

Lu and Pizzi [83] showed that lignocellulosic substrates have a distinct influence on the hardening behavior of PF-resins, whereby the activation energy of the hardening process is much lower than for the resin alone [84]. The reason is a catalytic activation of the PF-condensation by carbohydrates like crystalline and amorphous cellulose and hemicellulose. Covalent bonding between the PF-resin and the wood, especially lignin, does not play any role [84]. 

Amorphous adsorbents, 1 587-589 for gas separation, 1 631 properties and applications, l 587t Amorphous aluminum hydroxide, 23 76 Amorphous carbohydrates, material science of, 11 530-536 Amorphous carbon, 4 735 Amorphous cellulose, 5 372-373 Amorphous films, in OLEDs, 22 215 Amorphous germanium (a-Ge), 22 128 Amorphous glassy polymers, localized deformation mechanisms in, 20 350-351... 

The need of fully dependable information on the relative proportions of crystalline and amorphous cellulose in different cellulosic materials has given rise to a variety of approaches to the problem. These alternative methods in many instances fail to support X-ray findings and often show large discrepancies among themselves. It is the purpose of this... 

As a result of these studies it became evident that mechanical and chemical treatments may alter the relative amounts of crystallized and amorphous cellulose in a sample. For example, it was estimated that a normally coagulated viscose filament was about 40 % crystalline and 60 % amorphous while filaments of the same material, after being stretched, appeared to be 70% crystalline and 30% amorphous. This effect was observed to be more pronounced in cellulose derivatives than in unsubstituted cellulose where apparently the blocking of hydroxyl groups reduces the lateral forces of cohesion between chains, facilitates slipping and consequently promotes parallelization of chains. 

Amorphous Cellulose in Cotton and Cuprammonium Rayon by Periodate Oxidation"... 

Goldfinger and coworkers obtained the data shown in Table IX by this method. The difference in amorphous cellulose between linters and cotton is appreciable but attention is directed particularly to the behavior of cuprammonium rayon after being dried from water and after being... 

Evidence was presented that thallous ethylate did not penetrate or alter the crystalline parts of the fiber. Moreover, it was possible to conduct the thallation with different solvents for thallous ethylate. When this was done with normal ethers, the extent of methylation was observed to decrease as the molecular volume of the thallous ethylate solvent increased. These results suggested that accessibility is dependent upon the penetrating power of the ether solvent. Amorphous cellulose was, therefore, defined as the percentage of cellulose wetted by an ether of zero molecular volume and was estimated by determining methylation-molecular volume values for three or more straight-chain ethers, plotting the data and extrapolating to obtain methoxyl content for an ether of zero molecular volume. The amount of cellulose corre-... 

Amorphous cellulose, so defined, was reported for two simple but noteworthy modifications of cotton linters. First, linters which had been swollen with cold 10% sodium hydroxide, washed, and dried by solvent exchange prior to thallation and methylation, showed an amorphous content as high as 27 %. Secondly, unswollen linters appeared to contain only 0.25 to 0.50% of amorphous cellulose. Similarly, swollen ramie appeared to contain 18% of amorphous cellulose unswollen ramie, 0.25%. 

Unlike starch, which is amorphous, cellulose is fermented with difficulty because of its semicrystalline structure. As a consequence, ethanol fermented from cellulose using the latest generation enzymes would still be more expensive... 

The active sites of CBH II (or Core II), on the other hand, participated in the adsorption phenomenon both onto (semi)crystalline (Avicel) and amorphous cellulose. 

The hydrolytic activities of the intact enzymes were comparable, but CBH I was much more sensitive to product (cellobiose) inhibition. Both core enzymes exhibited a strongly reduced activity (50-90%) which was correlated with the absence of the binding domain and their consequent lower binding capacity on Avicel. The activities of CBH I and Core I on amorphous cellulose were, however, comparable. 

Although its two domains could function independently, removal of the substrate-binding domain of ngCenA reduced enzymatic activity against microcrystalline cellulose but not against CMC or amorphous cellulose (12). This suggested that the substrate-binding domain played a critical role in the hydrolysis of crystalline cellulose. 

Highly ordered crystalline cellulose has a density as high as 1.63 g cm whereas highly disordered amorphous cellulose has a density as low as 1.47 g cm 3. High-molecular-weight native cellulose, which is insoluble in 17,5% aqueous sodium hydroxide solution, is called alpha cellulose. The fraction that is soluble in 17.5% sodium hydroxide solution but insoluble in 8% solution, is called beta cellulose, and that which is soluble in 8% sodium hydroxide solution is called gamma cellulose. 

The Soviet authors Kargin et al. [35, 42] and Kozlov [43] have developed the theory of fully amorphous cellulose. Kargin and Leipunskaya [44] have drawn similar conclusions from an electron diffraction study of cellulose esters, including nitrocellulose. 

The glucose production from amorphous cellulose (by glucocellu-lase) and the cellobiose production from crystalline cellulose (by cello-biohydrolase, Ci) can be determined to assay the exo-/M,4-glucanase. 

Finally, the endo-/ -l,4-glucanase (Cx) can be assayed using amorphous cellulose, cellodextrins, or water-soluble derivatives by determination of the reducing sugars released or by viscosimetry. It is generally accepted that the release of reducing sugars is not a typical measure for the random action of endocellulases. 

CMC (50,53) amorphous cellulose (42) cellobiose through cellohex-aose (51)... 

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