Study of pitch colloidal stability using a Photometric Dispersion Analyser

This paper describes the use of a photometric dispersion analyser (PDA) to study and quantify the effect of wood resin preparation and salt on the colloidal stability of wood resin dispersions. The PDA technique has two major benefits over other techniques in that it can quantify the aggregation kinetics under dynamic shear conditions and at low concentrations of colloidal material. It is very sensitive to small changes in the solution and provides information about the floc structure and homogeneity. To ensure reproducible results when analysing colloidal wood resin dispersions, conditioning of the tubing and a constant flow rate and stirring rate were required. The PDA signal response with time for the wood resin dispersions shows three distinct regions: a growth region, a peak region, and a decay region. The slope of the initial growth region was used to measure the kinetics of coagulation and to determine the stability ratio, W. The critical coagulation concentration of different salts was also determined. The timeweighted variance of the PDA output showed that potassium salts resulted in more homogeneous aggregates than those formed with the addition of magnesium salts.