The effect of pH disturbances on the colloidal structure and fibre adsorption of Pinus radiata wood extractives

Experiments have been undertaken to investigate the effect of pH disturbances on the colloidal stability and phase distribution of Prudiala wood extractives. Adsorption experiments found that a perturbation of the pH resulted in increased deposition and lowering of the equilibrium concentration of the colloids in the water phase indicating a decrease in colloidal stability. Solubilisation of wood extractivcs from both the colloidal phase and the adsorbed state followed by re-precipitation of the wood extractives into the colloidal phase can explain the observed behaviour when the p11 is perturbed above 7 and then back to 5. When the perturbation is only 1-2 units from an original pH of 5 little solubilisation of the colloids occurs. It is proposed that changes to the interaction between the molecules in the colloid occur in this region which affect colloid structure and stability.