Carbohydrate behaviour of Arundo donax L. in ethanol–alkali medium of variable composition during organosolv delignification

The effect of medium alkalinity, organic solvent concentration and liquor-to-material ratio on the main carbohydrate constituents of Arundo donax L. stem (cellulose, hemicelluloses and uronic acids) under conditions of ethanol–alkali delignification has been examined. A protective action of alcohol addition against carbohydrate degradation was observed. The amount of non-cellulosic polysaccharides as well as the intrinsic viscosity of pulps increased with a rise in ethanol content in the reaction mixture. The increase in medium alkalinity was found to have a detrimental effect on carbohydrates and caused substantial loss of hemicelluloses. Elevated alkali and solvent concentrations were found to favour uronic acid groups degradation and hexenuronic acid formation during ethanol–alkali pulping. The liquor-to-material ratio had only some effect on uronic acid behaviour without any appreciable influence on cellulose and hemicelluloses.