Investigation of the fundamental physico-chemical properties of kraft black liquor

The fundamental physico-chemical properties of kraft black liquors (KBLs) have been investigated. These samples are obtained from an isothermal, 170 degrees C, a constant flow-through, 120 ml/min, laboratory pulping system at 15, 30, 60, 90, 120 and 150 min pulping time, respectively. It was found that the kraft black liquor (KBL) is a polymer solution with a lower surface tension and Hamaker constant than the original kraft white liquor. The reason is to be due to the presence of dissolved wood components, i.e., lignin, extractives and hemicelluloses. This suggests that these wood components are surface active. In this paper, the surface properties of kraft black liquor are discussed in terms of the Lifshitz-van der Waals (LW) force and acid-base (AB) interactions. It was found that all of these surface properties and the residual alkali as well as pH seem to be inverse proportional to the lignin concentration including of others dissolved wood substances. The viscosity and density of kraft black liquors are found varying proportionally to the concentration of lignin.