Effect of die exit stress state, Deborah number and extensional rheology on neck-in phenomenon

Abstract

In this work, effect of the second to first normal stress difference ratio at the die exit, uniaxial extensional strain hardening, planar-to-uniaxial extensional viscosity ratio and Deborah number has been investigated via viscoelastic isothermal modeling utilizing 1D membrane model and a single-mode modified Leonov model as the constitutive equation. Numerical solutions of the utilized model were successfully approximated by a dimensionless analytical equation relating the normalized maximum attainable neck-in with all above mentioned variables. Suggested equation was tested by using literature experimental data. It was found that approximate model predictions are in a very good agreement with the corresponding experimental data for low as well as very high Deborah numbers. It is believed that the obtained knowledge together with the suggested simple analytical model can be used for optimization of the extrusion die design, molecular architecture of polymer melts and processing conditions to suppress neck-in phenomenon in production of very thin polymeric flat films. © 2018 Society of Plastics Engineers. All rights reserved.