In a Fbeotens experiment, the tensile force needed for elongation of an extruded filament is measured as a function of the draw ratio. For thermo-rheologically simple polymer melts, the existence of Rheotens-mastercurves is proven. Rheotensmastercurves are invariant with respect to changes in melt temperature. Also, for polymer melts with different average molar masses, but similar molar mass distribution and branching structure, Rheotens-mastercurves are invariant to changes in the average molar mass. It is shown, by testing several polyethylenes with different molar mass distribution and different long-chain branching, that Rheotens-mastercurves allow a direct and quantitative assessment of the drawability of polymei-melts under actual processing conditions, i.e. under the action of a constant tensile force and including the effects of the rheological prehistory in the extrusion die.

The different methods that can be used for measuring the effect of a hydrostatic pressure on the viscosity of polymer melts are evaluated. A linear low-density polyethylene is chosen as test material, as it can be expected to have a small pressure dependency. Special attention is given to methods employing capillary rheometry, as these methods yield a range of shear rates and pressures that are typically encountered under polymer processing conditions. The accuracy of the different techniques is evaluated considering also the complexity of the experimental devices. First it is investigated to which extent standard capillary rheometry can be used to extract information about the pressure dependency of the viscosity. Secondly, it is shown how the accuracy can be greatly increased by the simple addition of a pressure chamber below the exit of the capillary, with a needle valve to regulate the back pressure. The results from this device are compared with those from a more robust method using a pressurized double piston rheometer and with literature data. The experimental values for the pressure coefficient of the viscosity will also be compared with those predicted from PVT data using Utracki's method.

Abstract3- and 4 parameter models (Carreau-Winter, Sabia, Yasuda) are used for fitting capillary rheometer tests. These fitted data are then compared with rotational visco-simeter test data in the region of small deformation speeds. The results clearly demonstrate that the extrapolated capillary rheometer data acc. to the Sabia and Yasuda models yield good practice-relevant results. A good correlation was achieved between the calculated “zero viscosity” and the mean molecular mass and between the model curvature parameters and the width of the molecular mass distribution. For quality assurance in laboratory rheometery and on-line rheometry these obtained good results are of high importance.

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