Exploring the utility of an axisymmetric semi-hyperbolic die for determining the transient uniaxial elongation viscosity of polymer melts

Abstract

The estimation of elongation viscosity of polymeric fluids from pressure drop measurements across converging dies remains an attractive method due to its cost effectiveness. However, the elongation viscosity so measured can be contaminated by large shear effects at the walls unless specific stress boundary conditions can be imposed. Such experiments are in general difficult to perform. In this work we examine an alternative simpler method that relies on a combination of experimental pressure drop measurements in semi-hyperbolic dies and matching viscoelastic CFD simulations to obtain the transient elongation viscosity data. The calculations of the transient uniaxial elongation viscosity from this methodology for an LDPE melt are compared with data obtained using extensional rheometers in order to explore the utility of the strategy.