Effect of Alkali Fsetreatment Gn Eucalypt Chips on Kraft Black Liqucr Viscosity and Pulp Strength

Higher viscosity of eucalypt kraft black liquor is apparently caused by a condensation of the poly-phenolic extractives with lignin during pulping. Extraction of the chips with 0.1–0.2 N NaOH at 115–125°c for 4 hours is suggested, prior to pulping, for removing most of the tannin-like material constituting about 1054 of plantation grown eucalypt (E. Tereticornls hybrid, 8–10 years old). Pulp yield. Kappa number and strength of a control cook with 16% active alkali are maintained with 13–14% chemical charge for the extracted chips. Viscosity data for black liquors at 80–100°C for concentrations up to 61% show lower values for extracted chips. The viscosity for 50% black liquor at 100°C decreases by one-third and two-third after pulping chips extracted with 0.l and 0.2 N NaOH, respectively.