Studies on Alkaline Digestion with Some Kind of Solutions (I)

Abstract

In a previous paper, it was assumed that the Sivola process gave a higher yield of pulp, because of the second stage alkaline digestion performed in the weakly alkaline region. So in this paper, various alkaline solutions were selected and used for alkaline digestion chemicals of unbleached sulfite pulp at high temperature. Yield, degree of polymerisation and other properties of digested pulps werecompared one another, and the results are as follows ;
1. The yield of pulp at a given alpha-cellulose level becomes lower according to the following order ; sodium borate or sodium borate+sodium sulfite, sodium carbonate+sodium sulfite, and sodium carbonate or sodium hydroxide (Fig.2-14, and Table. 3).
2. Pulp digested with a caustic solution is the lowest in the degree of polymerization and others are higher at all levels of alpha-cellulose content (Fig-3).
3. Sodium sulfite solution helps the dissolution of the degradation products from the carbohydrates of short chain length at the alkaline digestion and increases refining effect on cellulose (Table 2) as well as accelerates delignification on pulp.
4. It seems that the differences of pulp yields shown in item 1 are based on pH value of alkaline solutions and some actions of sodium sulfite above mentioned.