The role of β-O-4 cleavage in acidic organosolv pulping of softwoods

Fibres and fibre bundles of Norway spruce (Picea abies) thermomechanical pulp (TMP) were used as starting material for organosolv pulping. The solvents investigated were methanol, ethanol, propanol, acetone, dioxane and dimethyl sulphoxide at two or more volume fractions with water. An acid catalyst was required for significant delignification of the softwood and 0.005 mol/L H2SO4 was close to optimum at 175 degrees C. Delignification was significant for solvent mixtures having Hildebrand solubility parameters in the range of 11-15 (cal/cm(3))(1/2). The concentrations of beta-O-4 linkages in the woodmeal and pulp lignins were estimated by dioxane/HCl (0.2 mol/L) acidolysis. An excellent correlation between the yield of acidolysis products (mmol/g lignin) and lignin content after pulping was obtained for pulps cooked in 15 different solvent/water mixtures, with each formulation having its unique solubility parameter and acidity function.