Diffusion Controlled Kinetics of Electrolyte Transfer within the Pulp Fiber Wall: Estimation of Fiber Wall Pore Structure

Abstract

A kinetic model for diffusion of ions within the fiber wall is introduced. A good fit for the model was obtained with data from experiments, where diffusion of electrolyte through the fiber wall was studied by means of simple conductivity measurements. This model together with the respective experimental data makes it possible to study the pore structure of fibers.

For the experiments done the pore structure of fibers was first controlled by precipitating calcium carbonate within the fiber walls. It was found that the diffusion coefficient of ions within unfilled and calcium carbonate filled fiber wall was about 1 .5 and 0.5 % of that in water, respectively, when experiments were done for fibers without pit apertures. Experiments were made for fibers with different degree of drying as well. The results showed that the diffusion of electrolyte reduced with replicate dryings as expected. After the dryings, the diffusion coefficient was less than half of that within newer dried fiber.