The application of an acid prehydrolysis Step, even under very mild conditions, such as by the action of water or very dilute acetic or sulphurous acids for 1 h at 100â°C, allowed a great reduction in the duration of the alkaline pulping and resulted in significant changes in the properties of purified Egyptian cotton waste fibers. Alkaline pulping without a preceeding prehydrolysis Step produced a high α pulp with a high D. P. However, it was not reactive towards xanthation. A mild sulphurous acid prehydrolysis treatment resulted in still higher α-cellulose, higher degree of whiteness, high D. P. and better reactivity towards xanthation. The use of very dilute acetic acid in the prehydrolysis Step resulted in the same physical and sub-microscopic characteristics and the same reactivity äs in case of sulphurous acid. However, it gave rise to lower α-cellulose and lower degree of whiteness. A comparison between using low concentrations of weak and strong acids and under mild conditions in the prehydrolysis step revealed that the highest and lowest α-cellulose were obtained in case of sulphurous and acetic acids, respectively, and that sulphurous acid resulted in the best degree of whiteness. It also did not result in great differences in the swelling ability of cotton fibers, their crystallinity and their reactivity towards xanthation. Differences in pulp characteristics began to appear when the prehydrolysis was carried out under more drastic conditions. These differences were dependent upon the prehydrolysing acid and a wide variety of cotton pulps which differed in their specifications were obtained by intensifying the prehydrolysis conditions. A definite advantage of sulphurous acid is that it gave rise to pulps with higher degree of whiteness and which were composed almost completely of pure α-cellulose. © 1979, Walter de Gruyter. All rights reserved.
