Measuring the transient extensional rheology of polyethylene melts using the SER universal testing platform

Abstract

We use a new extensional rheology test fixture that has been developed for conventional torsional rheometers to measure the transient extensional stress growth in a number of different molten polyethylene samples including a linear low density polyethylene (Dow Affinity PL 1880), a low density polyethylene (Lupolen 1840H), and an ultrahigh molecular weight polyethylene (UHMWPE). The transient uniaxial extensional viscosity functions for the linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) samples have both been reported previously in the literature using well-established instruments and this allows us to benchmark the performance of the new test fixture. Transient stress growth experiments are carried out over a range of Hencky strain rates from 0.003 to 30s−1 and the data show excellent agreement with the published material functions. At deformation rates greater than 0.3s−1 a true steady state extensional viscosity is not obtained in the LDPE samples due to the onset of neckin...