Authors: Daniel Raps Thomas Köppl Lutz Heymann Volker Altstädt
Publish Date: 2016/12/27
Volume: 56, Issue: 2, Pages: 95-111
Abstract
The rheological properties of a long chain branched polypropylene LCBPP were investigated at the processing conditions of foam extrusion namely high pressure gas loading and high shear rates as well as in elongational deformation For measuring the rheological properties of PP at moderate and high deformation rates an inline rheometer was used Comparison of the results to standard rotational rheometry showed good agreement The effect of the processing parameters was quantified using shift factors for temperature pressure and gas concentration The influence of pressure on the shear viscosity was found to be of minor importance In contrast the shear viscosity was distinctly affected by CO2 concentration reducing it to one third of its gasfree value at a concentration of 6 wt at a specific shear rate The change of viscosity by a variation of temperature is similar in magnitude compared to the variation due to dissolved blowing agent Furthermore thermorheological complex behaviour was observed In the foaming process thermorheological complexity could contribute to a better morphology control of long chain branched polymers compared to linear ones The elongational viscosity was measured using both a hyperbolic die and a film stretching tool UXF for comparison It is almost three decades higher than the shear viscosity in the nonlinear region due to pronounced strain hardening of the meltThe financial support of the German Research Foundation DFG in the frame of the research project number Al 474/181 is highly acknowledged We also thank PD Dr Ulrich Handge Dr Sandra Aline Sanchez Vazquez and Prof HansMartin Laun for numerous scientific discussions Polypropylene was kindly provided by Borealis Polyolefine GmbH We thank Sebastian Gröschel and Markus Schirmer for experimental support
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