Studies on the wetting behaviour of polymer melts on solid surfaces using the Wilhelmy balance method

Abstract

A Wilhelmy balance method has been used to measure the wetting tension of polymer melts on solid surfaces at high temperatures. The application of thin quartz fibres or platinum wires allowed fast and reliable surface tension values for polypropylene and epoxy resin melts to be obtained without knowledge of the density of these melts. The measuring technique is also suitable for investigating the surface activity of additives or polar components in these polymer melts. The plot of γ cos Θ versus concentration for two commercially applied additives (benzoin, butyl acrylate) yielded different surface activities of these additives in an epoxy resin melt. The plot of γ cos Θ versus temperature provides different temperature coefficients of the wetting tension for each additive concentration. It was found that − d(γ cos Θ) dT was increased in the presence of the additives. The γ cos Θ versus temperature curves permit conclusions concerning the change in flow properties of polymer coating systems due to additives. Depending on the type of interaction at the solid/liquid interface — physical or chemical interactions — different wetting kinetics have been found for unmodified and chemiscally modified polypropylene melts on untreated and aminosilane-treated glass fibres. Thus, it is assumed that these measurements permit a more fundamental and quanttative understanding of the mechanism of interface formation in fibre-reinforced polymer composites.