ON THE MANUFACTURE OF WHEAT STRAW PULP BY AMMONIUM SULFITE PROCESS

Abstract

Wheat straw was chopped to the length of 1-2cm, pneumaticaly elutriated and shieved by screen. The ammonium sulfite solutions used for the cooking of the straw were prepared to pH 9 and pH 3 with sulfur dioxide and aqueous ammonium solution. The refined straw was cooked with 4 to 12% total sulfur dioxide on the weight of oven-dry straw at liquor-to-straw ratio of 10:1 and 5:1. The cooking was carried out at 180°C in case of the cooking liquor of pH 9 and at 150°C in that of pH 3. The pulps resulted were analysed chemically and the mechanical strength of their sheets was measured.The refining and screening of the semichemical pulp of straw were repeated several times under a definite condition. Each fraction resulted was chemically analyed.1. The maximum yield of screened pulp obtained with the cooking liquor of pH 9 and pH 3 is 54-56%, independent of chemicals and liquor-to-straw ratios.2. The lignin content of the pulps at maximum screened yield is varied from 5 to 9% in the cooking liquor of pH 9 and from 14 to 16% in that of pH 3.3. The pentosan content in the pulps at maximum screened yield is below 20% in case of the cooking liquor of pH 3 and over 20% in that of pH 9.4. The pulps of maximum screened yield with the cooking liquor of pH 9 are better than those at pH 3 in burst factor and breaking length.5. In the cooking at pH 9, the pulp of maximum screened yield increases in pentosan and decreases in lignin with increasing chemicals-to-straw ratio. The pulp at maximum yield of the screened obtained by cooking with a constant chemicals-to-straw ratio is slightly lower in lignin and pentosan in case of liquor-to-straw at the ratio of 5:1 than that of 10:1. As chemicals-to-straw ratio increases, the burst factor and breaking length of the pulp increase, while the liquor-to-straw ratio affects little upon these strengths.6. Semichemical pulp made from straw contains fractions having various lignin and pentosan contents.