The Role of Rheology in Polymer Extrusion

John Vlachopoulos
Department of Chemical Engineering

McMaster University
Hamilton, Ontario, Canada
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David Strutt Polydynamics, Inc.
Hamilton, Ontario, Canada

1.0 Rheology

Rheology is the science of deformation and flow of materials [1]. The Society of Rheology's Greek motto "Panta Rei" translates as "All things flow." Actually, all materials do flow, given sufficient time. What makes polymeric materials interesting in this context is the fact that their time constants for flow are of the same order of magnitude as their processing times for extrusion, injection molding and blow molding. In very short processing times, the polymer may behave as a solid, while in long processing times the material may behave as a fluid. This dual nature (fluid-solid) is referred to as viscoelastic behavior.

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