Using a by-pass-extrusion rheometer, which had been developed at the Department of Plastics Processing at the University of Leoben, two PVC-U compounds were characterized rheologically. The skin-component of a multilayer pipe was extruded with extruder speeds of 10 min-1 and 20 min-1. The measurements were carried out at three different melt temperatures and three slit heights of the rheometer. Increasing temperature results in higher slip velocities of the skin-component. At a temperature of 189°C and a shear stress of 0,45 bar a discontinuity of the slip velocity curve was found, where the rheological behaviour changes dramatically. These crictical conditions must be avoided for the extrusion of this material. A comparison between the results at extruder speeds of 10 min-1 and 20 min-1 showed that an increasing speed causes more lubrication, which can be realized in a parallel shift of the slip velocity curve to higher values.
The measurements for the second material, a compound for sewage pipes, were carried out at a speed of
20 min-1. For both melt temperatures of 188,5°C and 196°C, shear stress ranges with pure shear flow, ranges with shear flow overlapped by wall slip, and pure wall slip were found. The critical shear stress between these ranges was shifted to higher values with increasing temperature. At a temperature of 202°C no useful measurements could be carried out due to thermal degradation of the PVC.