Crystalline regions cellulose

Sulfate esters have also been prepared using preformed diafeylamide-sulfur trioxide (DMF.SO,) complexes. The reaction is heterogeneous but the complex can penetrate into the cellulose crystalline regions, producing highD.S. values) 2.0) and a very uniform distribution of the sulfate groups (31). 

It eonfirms the opinion [44, 56, 63] that water cannot penetrate cellulose crystalline regions. Thus, an inverse problem, namely, evaluation of the erystallinity degree based on thermoehemical data, can be solved. For example, using the enthalpy of cotton MCC interaction with water (AmixH= -3.5 kJ/mol of polymer) obtained in [48, 49] the degree of MCC erystallinity can be estimated using Eq. (1), this value being 86 %. 

In cellulose, crystalline regions coexist with non-ciystalline, amorphous domains statistically alternated along the fibril. Amount of amorphous phase in plant depends on the sample origin and, e.g., for Valonia it is 11%, while for primary walls of plants it reaches more than 70% [5,14]. 

Cellulose is the main component of the wood cell wall, typically 40—50% by weight of the dry wood. Pure cellulose is a polymer of glucose residues joined by 1,4-P-glucosidic bonds. The degree of polymerization (DP) is variable and may range from 700 to 10,000 DP or more. Wood cellulose is more resistant to dilute acid hydrolysis than hemiceUulose. X-ray diffraction indicates a partial crystalline stmcture for wood cellulose. The crystalline regions are more difficult to hydrolyze than the amorphous regions because removal of the easily hydrolyzed material has Htde effect on the diffraction pattern. 

Mercerized cellulose fibers have improved luster and do not shrink further. One of the main reasons for mercerizing textiles is to improve their receptivity to dyes. This improvement may result more from the dismption of the crystalline regions rather than the partial conversion to a new crystal stmcture. A good example of the fundamental importance of the particular crystal form is the difference in rate of digestion by bacteria. Bacteria from cattle mmen rapidly digest Cellulose I but degrade Cellulose II very slowly (69). Thus aHomorphic form can be an important factor in biochemical reactions of cellulose as well as in some conventional chemical reactions. 

Solid cellulose forms a microcrystalline structure with regions of high order, i.e., crystalline regions, and regions of low order that are amorphous. Naturally occurring cellulose (cellulose I) crystallizes monoclinic sphenodic. The molecular chains lay in the fiber direction ... 

Cellulose crystallinity has been shown to affect pyrolysis rates and Ea s (2,26,27). The initial low temperature decomposition is reported to occur first in the amorphous region (5,26,27). Also,... 

The elastomers exhibited rubber-like behavior. From an examination of electron photomicrographs of cross sections of the elastomers, the fibrillar structure of the cellulose fibers apparently formed a network, and poly (ethyl acrylate) was distributed uniformly among the fibrils. The rigid crystalline regions of the cellulose fibers apparently stabilized the amorphous, grafted poly (ethyl acrylate) to determine the mechanical properties of the elastomers (43, 44). For example, typical elastic recovery properties for these elastomers are shown in Table X. 

Because cellulose consists of regions of high and relatively low crystallinity, processes to disrupt cellulose operate at two levels intercrystalline and intracrystalline. The conditions required to swell intercrystalline regions are relatively mild, whereas drastic processes are required to affect the high-crystalline regions. These two areas overlap strongly but need to be distinguished. 

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