DISSOLVING PULPS FROM EGYPTIAN WHEAT-STRAW BY THE SODA PROCESS

Prehydrolysed Egyptian wheat straw was subjected to soda pulping and the effects of the duration of pulping and sodium hydroxide concentration on the alkali consumption, the yield, the chemical, physical and sub-microscopic characteristics of the pulps obtained, and their chemical reactivity (xanthation) were investigated. Higher alkali concentration enhanced delignification, had a favourable effect on the chemical and physical properties of the pulps obtained, and resulted in a more open and accessible fine structure and better chemical reactivity. The residual alkali remaining during pulping was necessary for the dissolution of the degraded carbohydrates and for improving the swelling properties of the pulps obtained. However, prolonging the time of pulping in the presence of higher residual alkali dissolved the more hydrophilic carbohydrate fractions and impaired the chemical reactivity. The only beneficial effect in this case was the higher rate of delignification. Moderate pulping time, together with higher alkali concentration were necessary to obtain a pulp with improved chemical, physical and sub-microscopic characteristics.