A collaborative study of capillary flow of a highly lubricated unplasticized poly (vinyl chloride)

Viscometric measurements carried out by ten members of the IUPAC Working Party “Structure and Properties of Commercial Polymers” is summarized and discussed. The participants in the study carried out steady flow measurements with capillary, slit, cone‐and‐plate and concentric cylinder apparatuses. Dynamic viscosities were determined with the Contraves Balance Rheometer. In this study a highly lubricated material with a relatively low molecular weight was chosen: highly lubricated to aid slip, low molecular weight to obtain a thermal transition at a relatively low temperature. The influence of capillary length and diameter on the flow curve has been the main subject of this study. Information supplementary to this was obtained with the other equipment. Above 180°C it was found that the flow curves obtained by the participants were consistent when account was taken of the lengths and radii used by the respective participant. The reason for this seemed to lie in the effect of hydrostatic pressure on the viscosity. There was no evidence at these temperatures of slip at the capillary wall. A change in the radius of the capillary did not alter the measured flow curve except at high shear rates when the effect of shear heating could be seen. Below 180°C there were indications that wall slippage or other, possibly structural, changes were taking place. However, strong evidence for this was not found by all participants and in some cases the findings were even contradictory.