The flow behaviors of a series of polyvinylchloride (PVC) resins covering a broad range of molecular weight have been examined at several temperatures. It has been shown that the influence of temperature on viscosity depends on the temperature range. That is, the flow activation energy is not constant but can be approximated by two values, one applicable to low temperatures, the other to high temperatures.The flow activation energy based on viscosities at constant shear rate decreases as the molecular weight increases. In contrast, the flow activation energy from viscosities at constant shear stress increases with molecular weight.The fact that the activation energy is dual valued does not seem to be associated with the polymer type. Both emulsion and suspension resins exhibit this behavior. Addition of certain modifiers appears to alter the activation energy at lower temperatures. These observations indicate that the shift in the activation energy in the low temperature range is due to a change in the flow mechanism.

The elasticity of polymer melts is of major concern in the processing of plastics. It is usually reflected by dimensional changes. Since the swelling of polymer extrudates depends on the capillary dimensions and the volumetric flow rate, the blow-up must be examined over a range of conditions, Of course, the swelling is also dependent on polymer structure. Consequently, variations in materials and operating conditions necessitate changes in tooling. This paper describes the swelling behavior of several different polymer types and illustrates that viscosity measurements can not be used to predict elasticity.

A method of treating experimental flow measurements on high polymers to obtain the basic shear diagram is described. Shear stress data are corrected to eliminate capillary end effects, and shear rate data are modified for the non‐Newtonian behavior of the materials. Differences in flow behavior of commercial low‐density polyethylenes are illustrated, and the effects of the two corrections are demonstrated. The method is applicable to other polymer melts. Although the data could be expressed by the power law, the fact that logarithmic plots of shear stress versus shear rate are not linear suggests that such relationships would be approximate. The data are expressed better by the threeconstant Powell‐Eyring equation, although the significance of the three parameters is uncertain. The need to obtain the rheological constants from the basic shear diagram rather than from an uncorrected or partially corrected capillary flow diagram is emphasized. In support of previous investigators, irregularities in the extrudate were observed at high shear stresses. However, it was not possible to determine at what pressure the roughness was initiated. The shear diagrams calculated from the experimental data do not exhibit any point of inflection as reported in some studies.

Studies of capillary extrusion measurements using an Instron rheometer show that certain types of high density polyethylene exhibit a discontinuity in the shear stress/shear rate curve. This behavior which is separate and distinct from the phenomenon of melt fracture is caused by a change in the flow regime. It is manifested by oscillation of the recorded load while the rheometer piston is operated at a constant rate. Therefore, this behavior has been termed “oscillating shear phenomenon”. The location and magnitude of the fluctuations are functions of the molecular parameters of the polymer as well as the melt temperature, capillary geometry, and other rheometer variables. Evidence is presented which indicates that the change in flow regime could result from the orientation of the melt as it enters the capillary.

A method is described to predict the time‐temperature behavior and hence thermal stability of PVC melts in a Brabender Plasticorder torque rheometer from basic rheological data(flow and thermal stability observations) obtained on an Instron capillary rheormeter. The predicted and experimentally determined values of the Brabender thermal stability are shown to be in good agreement.