The strain-hardening behaviour of linear and long-chain-branched polyolefin melts in extensional flows |
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Authors: | Manfred H. Wagner Heike Bastian Peter Hachmann Joachim Meissner Stefan Kurzbeck H. Münstedt F. Langouche |
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Affiliation: | Polymertechnik/Polymerphysik Technische Universit?t Berlin Fasanenstrasse 90 10623 Berlin, Germany e-mail: wagner@ikt.uni-stuttgart.de, DE Institut für Kunststofftechnologie Universit?t Stuttgart B?blinger Strasse 70 70199 Stuttgart, Germany, DE Institut für Polymere, ETHZ 8092 Zürich, Switzerland, CH Swiss F.I.T. Rheocenter, ETHZ 8092 Zürich, Switzerland, CH Institut für Werkstoffwissenschaften Universit?t Erlangen-Nürnberg 91058 Erlangen, Germany, DE Solvay & Co, 1120 Bruxelles, Belgium, BE
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Abstract: | By generalizing the Doi-Edwards model to the Molecular Stress Function theory of Wagner and Schaeffer, the extensional viscosities of polyolefin melts in uniaxial, equibiaxial and planar constant strain-rate experiments starting from the isotropic state can be described quantitatively. While the strain hardening of four linear polymer melts (two high-density polyethylenes, a polystyrene and a polypropylene) can be accounted for by a tube diameter that decreases affinely with the average stretch, the two long-chain-branched polymer melts considered (a low-density polyethylene and a long-chain branched polypropylene) show enhanced strain hardening in extensional flows due to the presence of long-chain branches. This can be quantified by a molecular stress function, the square of which is quadratic in the average stretch and which follows from the junction fluctuation theory of Flory. The ultimate magnitude of the strain-hardening effect is governed by a maximum value of the molecular stress, which is specific to the polymer melt considered and which is the only free non-linear parameter of the theory. Received: 1 June 1999/Accepted: 24 November 1999 |
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Keywords: | Strain-hardening in extensional flows uniaxial, equibiaxial and planar deformation linear and long-chain-branched polymer melts Doi-Edwards model molecular stress function theory |
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