HOW AFFINE IS THE ENTANGLEMENT NETWORK OF MOLTEN LOW-DENSITY POLYETHYLENE IN LARGE-AMPLITUDE OSCILLATORY SHEAR

The nonlinear viscoelastic behavior of molten plastics is often attrib uted to interactions between long-chain molecules. Entanglement theori es model this behavior with a network of junctions. Whether this netwo rk deforms differently than the liquid is a question of considerable i nterest to polymer engineers since nonlinear viscoelasticity governs m any plastics processing operations. In this paper, large amplitude osc illatory shear flow is used to measure hole affine the network deforma tion is relative to the deforming melt. Far a low-density polyethylene melt, a small amount of nonaffine network deformation is observed whe n the large amplitude oscillations are analyzed with a nonaffine struc tural network theory. Inaccurate predictions were obtained from both t he nonaffine network theory due to Phan-Thien, and the nonaffine netwo rk strand theory due to Larson.