Influence of poly(vinyl alcohol) molecular weight on drop coalescence and breakage rate

• Influence of polymer molecular weight on drop size.
• Transient drop size distribution in the presence of surface active polymer.
• Better drop stabilization by PVA of lower molecular weight.
• Good DSD prediction by multifractal breakage and coalescence model.

The influence of poly(vinyl alcohol), PVA, molecular weight on drop breakage and coalescence in stirred liquid–liquid dispersion was considered. Three types of PVA of the same degree of hydrolysis 88% and different molecular weights in the range 13,000–186,000 were used in experiments. Molecular weight affects steric forces, interfacial tension and surface viscosity, which all have an influence on drop size distribution. PVA of lower molecular weight reduces the interfacial tension more effectively while the adsorption of high molecular weight PVA is slower and more complicated. Drop interfaces can remain partially mobile for polymer concentration as small as 0.001 wt% or they can be significantly immobilized for PVA concentration c ≥ 0.002 wt%. Drop size distributions were predicted using multifractal breakage and coalescence models. Lost of stabilizing properties of PVA of highest molecular weight at high impeller speed was observed which can be explained by unfavorable molecule conformation in such conditions.