A comparison of extensional viscosity measurements from various RME rheometers |
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| Authors: | Jonathan S. Schulze Timothy P. Lodge Christopher W. Macosko Jens Hepperle Helmut Münstedt Heike Bastian Dino Ferri David J. Groves Yong Hoon Kim Mike Lyon Thomas Schweizer Terry Virkler Erik Wassner Wim Zoetelief |
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| Affiliation: | (1) Department of Chemical Engineering and Materials Science University of Minnesota Minneapolis MN 55455–0431, USA e-mail: macosko@tc.umn.edu, US;(2) Department of Chemistry University of Minnesota Minneapolis MN 55455–0431, USA e-mail: lodge@chem.umn.edu, US;(3) Institut für Werkstoffwissenschaften University of Erlangen D-91058 Erlangen, Germany, DE;(4) Institut für Kunststofftechnologie University of Stuttgart D-70199 Stuttgart Germany, DE;(5) Enichem Research Centre, Via Taliercio 14 46100, Mantova, Italy, IT;(6) IRC in Polymer Science and Technology Department of Physics and Astronomy University of Leeds, Leeds LS2 9JT United Kingdom, GB;(7) Toyota Technological Institute 2–12–1 Hisakata, Tempaku Nagoya 468–8511 Japan, JP;(8) ExxonMobil Chemical Company Baytown TX 77520, USA, US;(9) Institut für Polymere ETH Zentrum ML J16 Zürich CH-8092, Switzerland, CH;(10) Bayer Corporation, Indian Orchard MA 01151, USA, US;(11) BASF Polymer Research Laboratory ZKM/R-G 201, D-67056 Ludwigshafen Germany, DE;(12) DSM Research P.O. Box 18, 6160 MD Geleen The Netherlands, NL |
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| Abstract: | The transient uniaxial extensional viscosity η e of linear low density polyethylene (LLDPE) has been measured using the commercial Rheometric Scientific RME and the Münstedt Tensile Rheometer in an effort to compare the performance of available extensional rheometers. The RME indicated a significant strain hardening of the LLDPE, especially at a strain rate of 1 s−1. In contrast, the Münstedt rheometer showed the LLDPE to be only slightly strain hardening. This artificial strain hardening effect in the RME resulted from the strain rate applied to the sample, determined from the sample deformation, being up to 20% less than the set strain rate. These results initiated a round-robin experiment in which the same LLDPE was tested on several RMEs in various locations around the world. All but one of the RMEs indicated a deviation between set and applied strain rates of at least 10%, especially at strain rates above 0.1 s−1. The strain rate deviation was found to depend strongly on the value of the basis length L 0 , and may result from the upper pair of belts not properly gripping the sample during extension. Thus visual inspection of the sample deformation is necessary to determine the applied strain rate. The most accurate measurements of η e with respect to the strain rate deviation were obtained when the correct L 0 value and belt arrangement were used. A list of recommendations for running an RME test is provided. Future work focusing on the fluid mechanics during the test may identify fully the cause of the strain rate deviation, but from a practical point of view the problem can be corrected for in the determination of η e . Received: 27 September 2000/Accepted: 5 February 2001 |
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| Keywords: | Polymer melt Uniaxial extensional rheometry Instrumentation RME |
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