Influence of long-chain branching on the rheological behavior of polyethylene in shear and extensional flow

Abstract

In this work, a study of the influence of molecular struc- ture on the viscoelastic behavior of melts of commercial polyethylene (PE) copolymers, particularly in extensional flows, will be performed. To enable this study to be performed, a series of four very low-density polyethyl- enes (VLDPEs) (film and blow molding grades) with dif- ferent parameters of molecular weight (M W), molecular weight distribution (MWD), and degree of long-chain branching (LCB) will be used. Experiments in shear flow (steady state and oscillatory regime) are complemented with experiments in uniaxial extension (constant strain rate and stress relaxation after a step strain). It will be shown that a qualitative correlation exists between both types of experiments; the stress relaxation experiments being particularly sensitive to the different molecular features of the polymers. In addition, the failure behavior in extension was also investigated and the results indi- cate that, within experimental error, the Hencky strain to failure is sensitive to the type of molecular structure but the corresponding tensile stress is not.