A Critical Analysis of Using Step-Strain and Extensional Rheology to Obtain the Multi-mode 'Pom-Pom' Model Parameters for Branched High-Density Polyethylenes

The focus of this research is to evaluate the viability of using a rheological approach that combines shear step-strain and transient extensional rheology to determine the model parameters for the McLeish-Larson multi-mode pom-pom model for a series of structurally well-defined high density polyethylene. Presented here are two areas fundamental to this work. First is a novel encapsulation technique designed to overcome material failures ('necking') in transient extensional flow using a LLDPE sheath. Second is a discussion of the effect of branching content on time-strain factorability in step-strain.