Determination of phenomena involved in impregnation of softwood chips. Part 2: Alkali uptake, alkali consumption and impregnation yield

The influence of impregnation conditions on the phenomena involved in impregnation was studied with the aid of a new impregnation method. The method was found to be good enough for scientific research purposes and useful for gaining new knowledge of the alkali uptake, alkali consumption and dissolution of wood material during impregnation. An impregnation time of slightly over 15 min was found to be enough to transfer the required amount of alkali into wood for cooking, if presteaming and liquor with a high EA concentration were used. Most of the alkali was diffused into wood. It proved impossible to transfer enough alkali during 60 min impregnation using liquor with an EA concentration of 40 g NaOH/l. Besides, the amount of unconsumed free alkali inside wood was so small that this would involve a risk of running out of alkali, if the temperature is raised quickly to cooking temperature. Calculated impregnation yields were between 90 and 77% after 60 min impregnation, depending on the impregnation conditions. High impregnation temperature caused the biggest wood loss. Its influence on the yield loss was more remarkable than that of the amount of impregnated alkali inside chips.