Mercerized cellulose

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. 

Mercerized Cellulose (Mercerized Cotton). Mercerizatlon is a process of treating cotton with 25% Na hydroxide which causes it to shrink and become heavier, stronger, denser, and acquire a milky luster it will not shrink and is more easily dyed. It is more active and easier to nitrate than the original cellulose, but the resulting prod is not very stable... 

Those containing less than 7.5% N show a fiber character and give no X-ray diffraction indicating nitration, but only the pattern of mercerized cellulose... 

N are more or less disintegrated, yielding very diffuse diffractions, apparently due in part to very small crystalline elements of mercerized cellulose... 

The swelling of native, and mercerized, cellulose fibers in ethyl-enediamine (EDA), with subsequent washing in methanol, changes the cellulose I and II lattices to cellulose II] and III, respectively. The presence of EDA, in excess of that which is necessary for the cellulose-EDA complex to form, is essential for the conversion to occur. Treatment with boiling water or hydrochloric acid converts the III lattices into the respective, parent types. Washing in alkali converts both forms into cellulose II. 

Wilson and Miles [12] have measured the absorption of nitric acid by treating with it nitrocotton of 13.8% N. Under a pressure of 4 mm Hg as much as 15% of HN03, was absorbed by this nitrocotton. Nitric acid is absorbed better by a lowernitrated substance, just as the absorption of water vapour is easier in the case of lower-nitrated nitrocellulose. The maximum absorption has been established with nitrocellulose of 7% N. The amount of nitric acid absorbed by cellulose depends on its type. For native cellulose it amounts to about 25% by weight of the cellulose, and approaches 50% for mercerized cellulose. Such differences in the behaviour of different kinds of nitrocellulose indicates that swelling has an appreciable influence on absorption. Mercerized cotton which is more liable to swell simultaneously shows stronger absorption. 

Cotton thread treated with concentrated NaOH shrinks and has an increased luster. Tire resulting "Mercerized" cellulose has changed into other crystalline forms. The major one is cellulose II, in which the chains in the sheets are antiparallel.693 Cellulose II may also occur to some extent in nature. Many other modified celluloses, e.g., methylcellulose, in which some -OH groups have been converted to methyl ethers70 are important commercial products. 

The remaining questions in relation to the comparison made above is concerned with the appearance of two sharp bands in the IR and Raman spectra of mercerized cellulose, while only one such band is seen in the... 

Different. solubility behaviors were observed in organic solvent systems. Regenerated cellulose did not dissolve in the SOj-amine-DMSO system which, however, readily dissolved the native and mercerized samples [15-17]. Similarly, rayon and mercerized cellulose, unlike native cellulose, were insoluble in the dimethylformamide (DMS)-chloral-pyridine solvent system 114]. Thus, the morphology of the amorphous component in addition to its content plays a significant role in the overall reactivity of cellulose. 

Under similar acetylation conditions [153], the acetyl content of cotton (4.3%) was more than twice that of ramie (2.1%) or linen (1.3%) cellulose. Mercerization [8,154,155] greatly enhances the reactivity (or accessibility) of cellulose if it is maintained in a never-dried state. Drying of mercerized cellulose considerably reduced its reactivity to even less than half that of the unmercerized samples [8]. However, its impact, can be alleviated by dehydration through a solvent exchange process. The reactivity of mercerized samples expressed by acetyl content increased from 1.7% to 17.7% if water-washed sample was solvent-exchanged with pyridine and to 29% if washing directly with absolute ethanol and a subsequent pyridine exchange. 

In attaining a high alpha-cellulose with simultaneous removal of pentosan, there is a considerable loss of other material, presumably hexosan in nature. Although higher purity can be attained by treatment with cold, concentrated sodium hydroxide, this results in mercerization of the cellulose. Mercerized cellulose is of no use in the acetylation process unless it is specially treated in order to avoid inactivation by drying. ... 

Cellulose is a highly crystalline polymer composed of D-p-glucose units that are arrayed in chains with a polar axis and directionality (39). The two major crystalline forms of this polymer are native cellulose (form I) and regenerated or mercerized cellulose (form II). The present view is that, for cellulose I, all the chains in a crystal point in the same direction, that is, they are parallel, whereas for cellulose II, the chains in adjacent layers of a crystal are antiparallel (39). 

Mercerized celluloses absorb more water, have higher regains and more easily wet out than unmercerized fibres. Due to caustic soda penetration, many hydrogen... 

Figure 1. Ejects of grafting on pyrolysis products. Key O, char , tar O, water. A, mercerized cellulose B, carbamoylethylated and carboxyethylated...

Figure 5. TGA curves of unmodified and modified cellulose. A, mercerized cellulose (M) and carbamoylethylated and carboxyethylated cellulose (C) B, grafted samples of M and C C, stannic chloride treated cellulose of M and C D, stannic chloride treated cellulose of grafted samples.

TEMPO-mediated oxidation. With regenerated and mercerized celluloses, the oxidation leads to water-soluble p-l,4-linked poly glucuronic acid sodium salt (cellouronic acid, CUA) quantitatively [16]. In contrast, with native celluloses having the cellulose I crystal structure, the cellulose slurries maintain the slurry states even after TEMPO-mediated oxidation. These modified celluloses form water-insoluble fibers [17]. This has enabled modification of the surface of cellu-losic fibers. 

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