THE PULPING CHARACTERISTICS OF THE FOUR FRACTIONS OF WHEAT STRAW IN SODA-ANTHRAQUINONE COOKING

The pulping properties of the four fractions (node, leaf, joint and ear)of wheat straw were studied in soda-anthraquinone (AQ) cooking. The results show that delignification rate of the four fractions of wheat straw can be divided into three stages under identical cooking conditions: The bulk delignification stage from the beginning of the cook to 100癈; the supplementary delignification stage from 100癈 to 155癈; and the residual delignification stage from 155癈 to the end of the cook. In the first stage of the cook, 64-73% of lignin and 34-41% of carbohydrates in the leaf, joint and ear of straw are dissolved, about 72-74% of alkali is consumed; and 60% of lignin and 22% of carbohydrates in the node are dissolved, 44% of alkali is consumed. In the second stage of the cook, 37% of lignin and 12% of carbohydrates in the node are dissolved, 38% of alkali is consumed, whereas 23-31% of lignin and 11-16% of carbohydrates in the other fractions are dissolved, 17-21% of alkali is consumed. In the third stage, 1. 1% of lignin in the node is dissolved but 2-4% of lignin in the other fractions is dissolved. It is known from above results that there are evident differences in the pulping characteristics of the four fractions of wheat straw during soda- AQ cooking.