| Abstract: | Commercial, suspension-type PVC resin, poly (vinyl chloride), molecular weight Mw × 10?4 = 8.6 ± 0.9, polydispersity Mw/Mn = 2.26, was mixed with plasticizer di(2-ethyl hexyl)phthalate (DOP) and organo-tin stabilizer in four different proportions. The mixtures were milled and pressed into sheets for testing. The polymer content in these samples was 97, 80, 60, and 40 wt percent. The viscoelastic properties of the materials were investigated using a Weissenberg rheogoniometer in a cone-and-plate, steady-state shearing mode. The viscosities and primary normal stress difference coefficients were measured at shear rates of 10?2 ≤ \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^. $\end{document} (sec?1) ≤ 102 and at temperatures from 151 to 246°C. The zero shear viscosities, plotted as log η0 vs 1/T (T is the absolute temperature) did not follow either a straight line dependence, reported for PVC melts at low shear rates at 170–190°C, nor was any discontinuity found near 195°C as by others; the data follows a continuous concave curve. The apparent activation energy of flow increases steeply with decreasing temperature. The data can be represented by a WLF type of equation, but the magnitudes of the parameters of this relation differ from expected values. A crossplot of log η0 (T = const.) vs log w (where w is the polymer content) also demonstrates a faster increase of η0 with w than expected from the straight line dependence. The primary normal stress difference coefficient was found to increase with w and decrease with T, paralleling the observed dependencies of η0. |
