Swelling Complexes—Alkali Celluloses

Alkali celluloses are extremely important intermediates because they exhibit a markedly enhanced reactivity compared with original cellulose. The reagents can penetrate more easily into the swollen cellulose structure and thus react with the hydroxyl groups. For instance, preparation of alkali cellulose, named mercerization after its inventor John Mercer (1844), is an important step when producing cellulose xanthate, from which viscose fibers and cellophane are prepared. 

When cellulose fibers are mercerized in 12-18% sodium hydroxide solution, the original cellulose (cellulose I) is transformed into cellulose II and the unit cell dimensions are changed. This transformation, taking place at somewhat different concentrations depending on the origin of the sample, can be followed by X-ray measurements (Fig. 9-3). 

So-called inclusion compounds can also be prepared from cellulose. According to this technique water-swollen cellulose is dried via a series of solvents and the final solvent used is trapped inside the structure on drying. Although the embedded organic solvent has no stoichiometric relation to the cellulose, it has a property of activating cellulose for organic reactions. Such 

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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. 

The complex-formation of polysaccharides with alkali metals and alkaline-earth metals has already been discussed in this Series. A dextran-iron complex has been used in the experimental therapy of synovitis, and chondroitin sulfate-iron colloids have been prepared. The swelling of cellulose in aqueous solutions of zinc chloride depends on the formation of a complex with the vicinal 2- and 3- hydroxyl groups of the repeating unit. ... 

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