Surface Characteristics of Cotton Fibers as Indicatcd by Electro phoretic Studies

Natural cotton is composed of a primary and a secondary wall. The former forms a thin sheath on the surface of the fiber and is composed principally of small amounts of cellulose imbedded in a membrane of wax and pectic substance. The latter is composed principally of cellulose and forms the main body of the fiber. The pectic substance, although present to the extent of only approxi mately 1 percent, accounts for 85 percent of the total acidic groups of the mature fiber. The highly acidic nature and the location of this substance in the naturally-occurring fibers would be expected to influence greatly a number of the properties of the fibers, espe cially those dependent on surface characteristics. These surface characteristics are of considerable importance in a number of in dustrial processes such as, for example, the scouring, dyeing, and finishing of textile materials. Since the electrophoretic technique has been shown by research associates for the Textile Foundation at the National Bureau of Standards to be a useful tool for characterizing other fiber surfaces, it appeared advisable to apply it to an investigation of the cotton fiber as well. Samples of dewaxed cotton, cotton which had been depectinized by treatment with a boiling 1-percent solution of so dium hydroxide for various lengths of time, and pectic substance from cotton gave widely different pH-mobility curves. The curve for pectic substance is characteristic of a highly acidic substance whereas that of depectinized cotton shows a low order of acidity. The curve for dewaxed cotton appears to be a composite of the curves for cellulose and pectic substance. The purified cellulose exhibits a reversal of charge below pH 2.5, and accordingly is isoelectric at that pH. It is shown that the reversal of charge has not resulted from irreversible changes pro duced in the fiber during immersion in the dilute solutions of acid used in the present investigation.