STUDIES ON SULPHATE PROCESS

Abstract

Red pine and birch were cooked by the sulphate process under the conditions that the active alkali (expressed as Na2O) -to-wood ratio was kept constant at 20% and the sulphidity of the cooking liquor varied from 0 to 100% sulphidity at various times. The chemical and mechanical properties of the pulp of the same yields were studied within the range of semichemical and chemical pulp.The results obtained are as follows:1. To obtain the same yield, the cooking in 30 to 50% sulphidity requires the shortest cooking time. However, the sulphidity has no marked influence upon the cooking time to obtain the same yield in the range of semichemical pulp. (Fig. 2)2. In the case of red pine, value of lignin content in the pulp made at 75% sulphidity is the smallest and in the case of birch the pulp made at 100% sulphidity is the smallest. (Fig. 3)3. Relation between sulphidity and Roe number of pulp is similar to that of sulphidity and lignin contents. (Fig. 4)4. Pentosan content in the pulp of the same yield becomes larger with increased sulphidity (Fig. 5)5. The paper of red pine pulp which is made at 50 to 75% sulphidity has the highest value of breaking length, and that of birch pulp which is made at 15 to 50% has the highest value. (Fig. 6)6. The paper made of red pine pulp has higher value of burst ratio with increased sulphidity, and that of birch pulp has higher value of burst ratio with increase up to 50% sulphidity and the value is unchanged beyond 50%. (Fig. 7)7. The papers of red pine and birch pulps which are made at 30 to 75% sulphidity have the highest value of folding endurance. But, in the semichemical pulp, its value is almost unchangable except at 0% sulphidity.Summary: The cooking at 30 to 50% sulphidity is effectine for shortening cooking time and improving properties of the pulp.Provided that active alkali-to-wood ratio is kept constant and sulphidity is varied, we can get two sorts of pulp having the same yield, and one of these has a larger content of lignin and smaller content of pentosan while the other has smaller content of lignin and larger content of pentosan. Because of this fact, it is important to note whether the sulphidity used in making unbleached pulp is suitable or not for making the bleached pulp.