| Abstrakt: |
The prolonged action of molar sodium chlorite on hydrocelluloses at pH 2.9 and 20°C causes oxidation additional to the conversion of terminal reducing groups into carboxyl groups. Unmodified cotton cellulose is also oxidized under the same conditions after a period of induction of about 24 hours. It is believed that this oxidation is due to chlorine dioxide, which is gradually developed through decomposition of the chlorous acid present. The effect of aqueous solutions of chlorine dioxide on cotton cellulose at 20°C has been studied by measuring the rate of increase of fluidity, copper number, and carboxyl content. Unbuffered solutions (pH 2 to 3) with concentrations ranging from 0.28M to 0.80M, and approximately 0.27M solutions buffered at pH's ranging from 1.76 to 6.05 were used. Oxidation of the cellulose occurred under all the conditions employed, its rate increasing with increasing chlorine dioxide concentration and with increasing pH. The oxidation appeared to take place in two stages, viz. the formation of reducing groups and their conversion into carboxyl groups. Like the over-all reaction, the first stage was accelerated by increasing the pH, but the second occurred more rapidly at pH < 5 than at pH 6. Treatment of the chlorine dioxide oxycelluloses with 0.2M chlorite at pH 3 and 20°'C had little or no effect on their fluidities, but caused significant falls of copper number and rises of carboxyl content. The fact that the relation between fall of copper number and rise of carboxyl content was independent of the pH of the chlorine dioxide solutions used suggests that the nature of the primary oxidation is also independent of this pH. [ABSTRACT FROM AUTHOR] |
