Photometric Dispersion Analyser (PDA)to quantify pitch coagulation kinetics

The kinetics of coagulation/aggregation of the wood resin colloids under varying conditions of shear and ionic strength were investigated using a Photometric Dispersion Analyser (PDA) 2000. The PDA 2000 measures the turbidity variations of a moving colloidal suspension and monitors its aggregation/dissociation rate in terms of a stability ratio (W). This paper describes the use of the PDA 2000 to quantify and mathematically model the coagulation of wood resin colloids under dynamic shear conditions The PDA signal with time curves show several characteristic features: growth region, steadystate region, peak region, and lower steady-state region. These regions give information into the floc variation and growth. The slope of the initial growth region is a measure of the kinetics of coagulation. This is used to assess the validity of the Derjaguin, Landau, Verwey and Overbeek theory (DLVO theory) and the Reerink and Overbeek theory. The time-weighted ratio variance provides an indication of the severity of floc/aggregate break up as well as a measure of floc/aggregate structural homogeneity.