Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 38: Focus: Rheology II (joint focus with DRG)
CPP 38.10: Vortrag
Freitag, 30. März 2012, 12:00–12:15, C 130
An in-situ investigation of the draw resonance phenomenon in film casting of a polypropylene melt — Teodor Burghelea1, Hans Jurgen Griess2, and •Helmut Muenstedt2 — 1Universite de Nantes, Nantes Atlantique Universites, CNRS, Laboratoire de Thermocinetique de Nantes, UMR 6607, La Chantrerie, Rue Christian Pauc, B.P. 50609, F-44306 Nantes Cedex 3, France — 2Institute of Polymer Materials, Friedrich-Alexander-University Erlangen-Nu *rnberg, D-91058 Erlangen, Germany
An experimental investigation of the stability of the casting process of a polypropylene film is presented. Several flow regimes are identified: stable, oscillatory and chaotic. Measurements of the velocity distribution along and across the extruded film corresponding to each drawing regime are presented. The intermittent physical rupture of the film's edges observed within the chaotic drawing regime is explained by the emergence of a "V - shaped" region of high axial gradients of the axial velocity component which indicates a highly inhomogeneous distribution of tensile stresses. By measurements of the statistics of the fluctuations of both the film's width and velocity a continuous (second order) imperfect bifurcation towards oscillatory states is found. The fluctuation data acquired before the chaotic regime is reached can be fitted by the stationary Landau-Ginsburg equation. The observation of a stable limit cycle at the onset of the bifurcation identifies it as a supercritical Hopf bifurcation. The experimentally found scaling of the onset and amplitude of the bifurcation with the Weissenberg number indicates that elasticity destabilizes the drawing process.