Elongational viscosities of polymethylmethacrylate/nano-clay composites

The elongational flow of polymethyl methacrylate/nano-clay composites was studied during stressing and creep experiments using a Munstedt tensile rheometer (MTR). The dispersion of the nano-claywas controlled by means of transmission electron microscopy (TEM) and the layer distance was measured with X-ray diffraction (XRD). With growing volume fraction of the filler an increase of the viscosity is observed under constant strain rate and constant stress conditions. The results for the elongational viscosities for both modes are consistent with each other. Furthermore, a strain softening behavior can be measured, which is the more pronounced the higher the nano-clay content is. As the Trouton rule is not valid, deviations from the linear behaviour are related to an envolope curve for the elongational viscosities instead of the threefold zero shear viscosity.