High Temperature Leaching of Lignin From Unbleached Kraft Pulp Fibers

Abstract

When an unbleached kraft pulp was suspended in water at various temperatures between 20°C and 90°C the rate of the leaching of lignin from the fiber wall increased with the temperature. From 20°C to 70°C, the change in the intrafiber diffusion coefficient with temperature varied directly as the ratio of the absolute temperature to the viscosity of water, as expected for a diffusion process. Above 70°C, there vas a much larger dependence of the diffusion coefficient on temperature than was observed at the lower temperature. The change occurred near the glass transition temperature of the hemicellulose saturated with water, and may have been due to physical changes in the structure of the fiber caused by the thermal softening of the hemicellulose. Even at temperatures of 155°C, the handsheet properties of the pulp were not adversely affected by the leaching process.