Estimation of extensional properties of polyethylene melts from melt strength measurements

Extensional viscosity plays an important role in many polymer processes such as film blowing, fiber spinning, blow molding and sheet casting. Melt extension measurements have found widespread use in determining the extensional flow properties of different polymer melts as it is simple, reproducible and is representative of many polymer processes. All of these test results have been performed at a constant mass flow rate and can only represent a qualitative comparison of melt extension because of the non isothermal stretching and prehistory of the polymer melt in the die and extruder. This paper is aimed at studying how uniaxial melt extension experiments for polyolefins can be used to estimate the transient extensional viscosity. An analytical Wagner model in the linear region of the drawing test was used to calculate the transient extensional viscosity. An optimal extrusion and drawing parameters for a reliable drawing test were obtained so that true and accurate melt strength of a polymer could be obtained. Later, these results were compared to the transient extensional viscosity obtained from a constant strain rate Rheometrics Melt Extensional (RME) rheometer. The results agree within the measurement accuracy with those measured from RME. Thus, extensional viscosity calculated from uniaxial melt extension experiments can be used to estimate transient extensional viscosity