The effect of different batches of the same polymer on the flow in flat coextrusion dies

Abstract

Rheological and molecular characteristics (MWD) were experimentally determined for different batches of LDPE. The results show that extensional viscosity may significantly vary for different batches even if shear viscosities and MWDs are very similar. FEM analysis was consequently performed to determine the stability of the coextrusion flow in the flat die for different batches of the material and the effect was found considerable. A recently proposed 'TNSD sign criterion' (Zatloukal et al, Int Polym Proc., 16(2) 198-207 2001), which quantifies the relative stretching of the layers in the merging area, was used for this purpose.