Theoretical and experimental investigation of wave interfacial instabilities at coextrusion in flat dies

Abstract

The work presents both, simulation and experimental findings of the research of two LDPE melts using a flat coextrusion flow visualization cell. The simulation is performed by FEM analysis with full u-v-p-τ numerical scheme employing viscoelastic constitutive equations. The predicted stresses, velocities and interface location have been found to be in a good agreement with the measurements. The experimental analysis shows that pronounced wave instabilities are caused by the minor layer break at the merge point of the layers, and extensional viscosity is a driving parameter here. Finally, recently proposed 'TNSD sign criterion' has been successfully tested for the prediction of the onset of wave interfacial instabilities in this type of the die geometry.