(602g) The Sensitivity of Extensional Rheology to Long Chain Branching in Commercial Polyethylene Samples

The ability to engineer the rheological response of polymeric materials is of great interest to both academia and industry. Efforts in this area include blending polymeric architectures and molecular weights to achieve a prescribed linear and nonlinear shear response of the material. Unfortunately, the bulk of these efforts are trial and error approaches that afford little in the way of predictable processing conditions. Recent work from our group demonstrated the lack of correlation between linear shear response and nonlinear response of long branched chains, such as low-density polyethylene, in extensional flow. Since most processing flows are dominated by extensional flows, more work is needed to better understand the effects of formulation and long chain branching on nonlinear extensional viscosity. In this work, we examine four industrial high-density polyethylene (HDPE) samples in linear shear and nonlinear extension. Small amplitude oscillatory shear shows very little differences in the HDPE samples. Using the van-Gurp Plamen plot, we identify samples with long chain branching and make correlations to nonlinear extensional viscosity. When possible, the results are put into the context of molecular weight and polydispersity as reported by the supplier. We demonstrate the sensitivity of creep compliance and rate dependent strain hardening on long chain branching, average molecular weight, and PDI. Overall, extensional rheology is shown to be very sensitive to polymer formulation and with sufficient well-characterized samples could lead to predictive tools to engineer nonlinear rheological behavior.