A comparative experimental study of the isothermal shear and uniaxial elongational rheological properties of low density, high density and linear low density polyethylenes

Abstract

The rheological properties of a series of sixteen polyethylene melts with different molecular weights, molecular weight distributions and types of long chain branching have been investigated. Measurement of shear viscosity, principal normal stress difference and elongational flow response are included. The behavior of high density polyethylenes and linear low density polyethylenes are described in an equivalent way in terms of their molecular weights and molecular weight distribution. The LDPE response is different, being strongly influenced by the extent of long chain branching. This appears to elevate normal stresses, and introduce substantial “strain rate hardening” in uniaxial extension. The experimental data are interpreted in terms of the theory of second-order fluids and the convected Maxwell model. The influence of long chain branching as well as molecular weight distribution on constitutive equation parameters is discussed.