Fundamental Studies on the Process of Wood Cooking (II)

Abstract

Again we took shavings as thin as 200 μ from ezomatsu (a kind of spruce in Hokkaido, Japan) and cooked them by soda process. While cooking, we measured 1. the amount of removed lignin, pentosan and cellulose.2. the change of “degree of polymerization” (D.P.) 3. mechanical properties of residues and their products which were delignified with NaClO2. The results were compared with that from the previously reported sulfate cooking.The speed of cooking reaction and consumption of effective alkali was slower in the case of soda cooking than sulfate cooking. However, the amount of removed lignin, pentosan and cellulose for the same yield of residue was almost as same throughout the whole stage of cooking regardless of the cooking process. The “D.P.” and the values of the mechanical properties of delignified soda pulp reached their maximum at such a high yield as 70% and then began to fall gradually as the yield of residue decreases. In case of sulfate process, it was found that the maximum value of D.P. and maximum mechanical strength appear at the yield of 40-50%. Since the residues could easily be defibrated at the yield of 40-50%, the mechanical properties of soda pulp obtained at such yield are always quite inferior to those of sulfate pulp whichhas the same yield.The reason why the remarkable degradation of cellulose occurs at the later stage of soda cooking is probably hat the cellulose has been exposed to stronger effective alkali for a longer period of time at high temperature. This will also explain the smaller D.P. s and lower values of strength of soda pulp than sulfate pulp.