INVESTIGATION UPON DISSOLVING PULP (PART VIII)

Abstract

With the same samples described in parts V, VI and VII, the morphological transformation of wood cellulose fibers during sulfite cooking, hot alkaline purification and hypochlorite bleaching was investigated by modifying Heide's phosphoric acid method. (K. Heide, Faserforsch. u. Textiltechn., 3, 469 (1952)).The swelling and dissolution state of cellulose fiber at each pulping stage in 78, 79 and 80% H3PO4 was observed by phase-contrast microscope. Simultaneously, the determination of haze value of cellulose solution in 79.5% H3PO4 was also carried out as a newly proposed method by us for estimation of cellulose reactivity.The results ware as follows:1. The swelling and dissolution state of sulfite-cooked cellulose fiber (further delignified with NaClO2)in phosphoric acid was improved with decrease in its average D. P. during the sulfite cooking.2. As a result of subsequent chlorination, hot alkaline purification and hypochlorite bleaching, the state of swelling and dissolution of cellulose was further improved. The final hypochlorite bleaching, however, did not contribute too much to its improvement as the former did. Though the influence of DP of the original sulfite cooked pulps upon the state of swelling and dissolution of cellulose in phosphoric acid was gradually decreased with the subsequent pulping processes, its effect was still slightly observed in final bleached pulps.3. The determination of the haze value of cellulose solution in 79.5% H3PO4, newly proposed by us, may be a good method for quantitative estimation of reactivity of cellulose.The results by this method was very much consistent with that of microscopic observations, and also with the results reported in Part VII on clogging constant (Kw) of viscose prepared from these samples.