ONLINE MONITORING OF DROP SIZE DISTRIBUTIONS IN AGITATED VESSELS .2. EFFECT OF STABILIZER CONCENTRATION

Surface-active agents play a very important role in the production of polymers by suspension polymerization. Their function is to absorb to the monomer/water interface, thus, preventing coalescence of monomer droplets. One commonly used stabilizer is poly(vinyl acetate) partially hydrolyzed to poly(vinyl alcohol) (PVA). The degree of hydrolysis and the molar mass of PVA affect its ability to act as a stabilizer. To assess the effectiveness of PVA in stabilizing monomer drops, a model system of 1 % styrene in water was selected for our experimental studies. The stabilizer had a viscosity average molar mass of 22 000 and a hydroxyl group content of 97.5-99.5 mol %. The interfacial tension of the styrene/water system was measured by the Wilhelmy plate method for various concentrations of PVA. A number of experiments were carried out to study the effect of stabilizer concentration on the evolution of drop size distribution. The minimum time required for a system to reach steady state and the corresponding average drop diameters were measured as a function of stabilizer concentration, temperature, and agitation speed. Correlations were developed to relate the minimum transition time, t(min), and Sauter mean diameter, d32, with the Weber number of the main flow.