Study of the Effect of an Antifoaming Agent on the Evaporation of the Components During the Stirring of a Coating Dispersion Containing a Volatile Agent

The main objective of this work was to evaluate the evaporation of coating liquids containing a volatile component (ethanol) and an aqueous polymer dispersion under well‐controlled circumstances. The influence of different concentrations of a polydimethylsiloxane type antifoaming agent was studied. In consequence of to its low interfacial tension, it can form a layer on the surface of a liquid, and the effect of this was studied by determination of the quantity of the stirred liquid that was evaporated. The effects of different operational factors were compared by means of factorial designs. It was conluded that the presence of ethanol in the liquid changed not only the extents of the effects of the factors, but also their relative importance as concerns the evaporation process. The highest difference in effect of a given factor was detected for the stirring rate, while the lowest difference was observed for the duration of stirring. A high concentration of Dimeticon decreased the extent of evaporation, but not significantly. Thus, the alterations in the effects of the operational factors were not very substantial either. It may be stated that this antifoaming agent does not result in a relevant change in the evaporation in these systems containing ethanol as a volatile component. Accordingly, primarily the operational parameters must be considered during the formulation of these compositions. This information helps towards the design of an appropriate stirring device, because our results indicate that open systems are not adequate and it is known that hermetically closed tanks make atomization impossible. Hence, determination of the critical control points of coatings with a liquid containing a volatile component cannot be avoided because the vapour of such materials can be very dangerous.