Mercerization complexes

Figure 4.8. The 2 1 complex of KNCS with dibenzo-24-crown-8 (Fenton, Mercer, Poonia Truter, 1972).

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. 

A much more extensive investigation of the effect of alkalies has been made in the case of polysaccharides, especially cellulose this is understandable in view of the industrial importance of mercerization, of the viscose process, and of cellulose ethers. Various complexes have been reported for cellulose and alkalies depending upon the nature of the alkali, upon its concentration, upon the washing treatment used, and upon the pretreatment of the cellulose. A discussion of this subject has been published by Nicoll and Conaway.84 There is general agreement on the formation of several compounds, which are susceptible to hydrolysis. The question as to whether these compounds are molecular complexes (XLVII), true alkoxides (XLVIII), or an equilibrium mixture of the two has not been answered. In recent studies Lauer65 has reached... 

The effects of cellulase enzymes on cotton substrates that were dyed with various classes of dyes have been reported. It was found that vat dyes do not inhibit cellulase activity on cotton, and hydrolysis of the substrate with subsequent color removal transpires. In contrast, cellulase activity on cotton was inhibited by the presence of some direct and reactive dyes. There is the probability that a dye-enzyme complex is formed with less activity than that of the free enzyme. The increased weight loss from enzymatic treatment on untreated cellulose is associated with a slight reduction in dye sorption, and this may be because of a reduction of amorphous regions in cellulose where dye molecules are usually sorbed. Cellulase activity is more prominent on mercerized cotton than on unmercerized cotton. This is because mercerization is associated with a decrease in the crystallinity of the cellulosic structure [540]. One major negative aspect of cellulase treatment of cotton fabric is the strength loss associated with the approximately 3-5% weight reduction under normal treating conditions. Of course, this is to be expected after cellulose is hydrolyzed. Future research efforts may lead to processes in which enzymes... 

Sarko, A., Nishimura, H., and Okano, T., Crystalline alkali-cellulose complexes as intermediates during mercerization, in The Structures of Cellulose, Atalla, R.H., Ed., ACS Symposium Series, No. 340, American Chemical Society, Washington, D.C., 1987, p. 169. 

Figure 11.21. Golgi Complex and Endoplasmic Reticulum. The electron micrograph shows the Golgi complex and adjacent endoplasmic reticulum. The black dots on the cytoplasmic surface of the ER membrane are ribosomes. [Micrograph courtesy of Lynne Mercer.]...

The preceding discussion of the industrial products obtained from cellulose while not complete nor in technical detail emphasizes the striking fact that cellulose, a widely distributed natural substance, complex in its constitution and inactive in its properties, may, by either mechanical treatment or chemical reaction, be converted into such important products as thread, string and rope wearing apparel (cotton and linen). Mercerized cotton, artificial silk collodion, celluloid, smokeless powders and high explosives. 

Strong alkali solutions acting on cellulose (at room temperatures) produce alkali cellulose. The studies on the structure of alkali cellulose [43] obtained with 20-40% NaOH solutions indicated that the substance is not a true alcoholate but an addition complex, RceiiOH NaOH. A true alcoholate can be obtained, for example, from dry cellulose and Na in liquid ammonia. Alkali cellulose has a large range of applications as an intermediate product in the preparation of cellulose ethers, and xanthate (dithiocarbonate), as well as in cellulose mercerization. 

Because of the demand for solving environmental problems and the explosion of computing power at ever reduced prices, there has been tremendous growth in models of coupled processes. Nevertheless, the complexity of nature and demands on computing power still preclude models that include all the processes discussed above. Very often we are forced to consider simplified subsets of the general problem (Mercer and Faust, 1981). 

Crystalline Alkali-Cellulose Complexes as Intermediates During Mercerization... 

As can be seen in table 2, a number of unit cells have been proposed for cellulose I-hydrazlne complexes over the years. Some of this diversity is almost certainly due to poor quality data, which can be Indexed in different ways. Nevertheless, visual comparison shows that our patterns are significantly different from those published previously, which probably reflects the fact that we used hydrazine containing no more than 3% water, as compared to up to 40% in earlier work. So far we have prepared three different cellulose Il-hydrazlne complexes, two for Fortisan (designated A and B) and one for Mercerized ramie. There may be some rationale for this complex A has only been obtained using anhydrous hydrazine, and the Fortisan and Mercerized ramie have different morphologies. However, it seems likely that all three complexes can be formed by both specimens once the preparation conditions are better understood. 

In the previous work in which (H- and )3c-NMR were used (17), the dissolution of cellulose in the SO2-DEA-DMSO system has been explained in terms of complex formation between the -OH of cellulose, and SO2 and DEA, as shown in Figure 1. The pattern of solubilities noted earlier suggests that the complex formation reaction in Figure 1 is specific to particular intra- and/or intermolecular hydrogen bonding patterns peculiar to native and mercerized celluloses. 

Mellor traced this idea of association of molecules by residual affinities to Mercer and Playfair it was adopted by H. E. Armstrong, and J. W. Walker. The idea of an intermediate complex appears in the work of W. Higgins (1789 see Vol. HI, p. 745) and in Dalton s note-books. Kekule s scheme of reaction (3) implies the modern theory of the intermediate complex , since he said ... 

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