Abstract
It is well recognized that cellulosic materials contain acidic groups which bind ions and accordingly influence the electrical conductivity, the dyeing, and the finishing of the fibers or fabrics.
In an earlier investigation, the relationship between the ash content of cotton fibers and their acid-binding capacity was devel oped. To study further the acidic properties of cotton, the investi gation has now been extended to include the direct estimation of the acidic groups in the fiber by titration with alkali. Both mono valent and divalent cations were used in this work.
When dewaxed cotton is freed of its cationic ash electrodialyti cally, it binds a maximum of 0.065 milliequivalent per g. of either silver or calcium ions, while depectinized cotton binds only 0.010 milliequivalent per g. These values confirm previous estimates of the carboxyl contents of these samples obtained by titration with acid. The identity of the base-binding capacities when mono- and divalent ions are used is a strong indication that the binding of these ions results from an acid-base reaction rather than from some undefined adsorption process. This conclusion was substantiated by esterifying the acid groups of eelctrodialyzed depectinized cot ton with diazomethane, which thus reduced the base-binding ca pacity to nearly zero.
It is shown that the maximum silver-binding capacity can be obtained only by the use of the silver salt of a very weak acid. When the salt of a strong acid is used a sufficient number of hy drogen ions are in the solution to compete with the silver ions for the acidic groups of the fiber.
The silver-binding capacities of electrodialyzed dewaxed and electrodialyzed depectinized cotton are greater than those of de waxed and depectinized samples, respectively. This result is ex plained in terms of competition of silver ions with the cations already on the acidic groups of the fiber.
The number of acidic groups in depectinized cotton is not altered by progressive treatment of the fiber with alkali, a fact which lends support to the tentative conclusion that the acidic groups in depectinized cotton are an integral part of the cellulose molecule.
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