How Affine is the Entanglement Network of Molten Low-Density Polyethylene in Large Amplitude Oscillatory Shear?

Abstract

The nonlinear viscoelastic behavior of molten plastics is often attributed to interactions between long-chain molecules. Entanglement theories model this behavior with a network of junctions. Whether this network deforms differently than the liquid is a question of considerable interest to polymer engineers since nonlinear viscoelasticity governs many plastics processing operations. In this paper, large amplitude oscillatory shear flow is used to measure how affine the network deformation is relative to the deforming melt. For a low-density polyethylene melt, a small amount of nonaffine network deformation is observed when the large amplitude oscillations are analyzed with a nonaffine structural network theory. Inaccurate predictions were obtained from both the nonaffine network theory due to Phan-Thien, and the nonaffine network strand theory due to Larson.