THE CHEMICAL ANALYSIS OF COTTON—OXYCELLULOSE, Part I

Abstract

Abstract Some of the commonest faults encountered in finished cotton fabrics are traceable to the effects of oxidising agents on the cellulose, whereby this acquires new properties. Methods by which this detrimental change can be detected in its early stages are most necessary, and therefore the existing tests have now been examined critically in order to judge of their merits and to learn how to interpret the information they furnish. As a basis of comparison for the tests, standard methods are described for the preparation of oxycelluloses. On investigation, the products are found to fall between two extreme types of oxycellulose, one characterised by great affinity for Methylene Blue and abnormal retentive power for alkalis, the other by high reducing power (as expressed by the copper number) and excessive loss of weight in scouring. If cotton has been so affected by oxidising agents that the second type of oxycellulose has been produced in it, it regains its original chemical properties on scouring with alkali, though, of course, suffering loss in weight. A determination of the copper number will not therefore reveal such tendering by oxidising agents as leads to the formation of this second type of oxycellulose if the material has been scoured after bleaching. The measurement of the viscosity of a solution of the cotton in “cuprammonium” does, however, reveal changes in the cellulose, no matter what the conditions of oxidation or the subsequent treatment may have been. On the other hand, other changes beside those caused by oxidising agents may bring about the same reduction in viscosity, but this is not likely to happen as the result of a normal alkali scour. The copper number is recommended as a useful criterion of the permanence of white in bleached cotton, the Methylene Blue absorption as an indication of level-dyeing properties, and the viscosity as a means of detecting tendering in a normal process of scouring and bleaching. Which type of oxycellulose is produced predominantly in a given bleach depends chiefly on the acidity or alkalinity of the hypochlorite solution. On the alkaline side of the neutral point the product has a high Methylene Blue absorption and low copper number, but on the acid side the absorption is low and the reducing power great. The value of various qualitative tests is also discussed.