STUDIES OF SEMICHEMICAL PULP

All cookings in this report were performed under the following conditions except the addition of alkaline chemicals:Total:- SO2 2.5%, Liquor to wood ratio:- 5:1Time required to raise from 20°C to 185°C (cooking temperature) 100 minutesCooking time:-120 minutes in the case of cooking of the red pine 30 minutes in the case of cooking of the birch.For the first case we cooked the red pine and the birch without adding of alkaline chemicals, and the pulp yields from both woods resulted in 67%_??_68%. Then we added alkaline chemicals to the cooking liquor, and studied the effects of addition of chemicals upon the cooking state and the properties of paper made of the pulp obtained.(1) When the cooking liquor involves sodium hydroxide or sodium carbonate, the velocity of digestion is accelerated and sodium hydroxide shows faster cooking than sodium carbonate does.The cooking velocity is no more accelerated when sodium hydroxide of sodium carbonate is added over a certain limit. When sodium hydroxide is excessively added to the cooking liquor, it works as the cooking reagent and impedes sulfonation of lignin by sodium sulphite.(2) The alkaline chemical suitable for the purpose of buffering action is sodium bicarbonate, and sodium hydroxide and sodium carbonate indicate no buffering action and work only as pH controlling reagent which keep in order that the cooking liquor may no turn acidic while cooking. The addition of calcium carbonate to the cooking liquor shows also no buffering action.(3) When the concentration of sulphur dioxide in the cooking liquors is kept constant, the mechanical properties of paper made of pulp obtained are not affected by the amounts and kinds of added alkaline chemicals, but closely depend upon the yield of pulp.(4) In the range of semichemical pulp, Roe number is relative to the yield of pulp, but the change of Roe number is very small in comparison with the change of the yield of pulp.(5) In the definite cooking time, it is worth noticing that lignin content in pulp increases notwithstanding the decrease of yield, when alkaline chemical is added to the cooking liquor.(6) In the cooking of birch, the increase of cooking pressure caused by carbon dioxide gas from sidium carbonate or sodium bicarbonate is negligible, if they are not excessively added to the cooking liquor.(7) The color pulp cooked by the liquor without any alkaline chemical is the lightest, and the more alkaline chemical added to the cooking liquor, the worse becomes the color of the pulp. In this case, jt becomes more brown in the red pine and more reddish-brown in the birch.