Measurement ond Modelling of Polymer melt Flow and Extrudate Swell
Timothy Nicholson, Oliver Harlen, Alexi Likhtman, Tom McLeish
University of Queensland
Australia

Keywords: melt-flow, finite-element, pompom

---

Various polyethylenes (low density and high density) and polystyrenes (monodisperse linear, H and comb) were observed flowing through a 10:1:10 constriction in a multi-pass rheometer, developed at the University of Cambridge. In this the flow is assumed to be planar and observations can be made of the birefringence, and pressure drop across the constriction. The birefringence pattern in the outflow was observed to be a qualitative measure of the degree of branching.

The polyethylenes were also extruded through a 15mm die of diameter 3mm and the extrudate dimensions recorded. The observed die swell increased with shear rate up to a rate of 10s^-1 and then decreased at higher shear rates. In all cases the extrudate swells rapidly upon exit from the die and then continues to expand more slowly.

The same materials were rheologically characterised (shear viscosity and extensional data) and these data used to fit the necessary parameters for constitutive models. Two constitutive models were evaluated: the multi-mode pom-pom equation, designed to model branched polymers, and the ROLIEPOLY (ROuse LInear Entangled POLYmer) equation, designed to model linear polymers. Simulations of the flow and extrusion processes were then performed using a Lagrangrian finite element flow solver developed at the University of Leeds. For the extrusion process non-isothermal effects had to be included in the models. The simulations showed good agreement to the experiments.