Dissolved and colloidal substances from a mechanical pulp suspension—Interactions influencing the sterical stability

The stability of colloidal material present in unbleached thermomechanical pulp suspension was studied by investigating the influence of simple electrolytes as a function of temperature and substrate concentration. The influence of competitive adsorption to kaolin was also studied. The results indicate that when the temperature is raised, a decrease in the stability of the suspension occurs. The stability was further decreased by addition of simple electrolytes as well as by decreasing the pH. When increasing the substrate concentration, the suspension seems to become less sensitive to electrolyte induced flocculation. This indicates that in concentrated suspensions the contribution of the sterical component of the stabilization mechanism is greater and that in diluted systems other stabilization mechanisms are also important. Adsorbed polymers are proposed to largely determine the surface properties of the lipophilic extractives. Kaolin was found to influence the stability of the lipophilic extractives resulting both in a decrease of the amount of lipophilic extractive droplets in the dispersion, as well as rendering the droplets sensitive to electrolyte induced aggregation.