Study of the Hydrodynamic and Viscoelastic Properties Affecting the Surface Appearance of Extruded EPDM Compounds

An experimental study was aimed at understanding the mechanisms establishing the surface appearance of extruded EPDM compounds for applications where aesthetic appearance is critical. The study shows that surface appearance is directly proportional to the extent of viscous heating in the die, and hence can be controlled by the degree of shearing action, either by screw and die design or screw speed. Both surface appearance and extrudate swell can be related to the viscoelastic properties of the EPDM polymer through the dimensionless Deborah and Euler numbers. Knowledge of the parameters affecting surface appearance can be applied to better design of EPDM polymers for such applications as automotive seals for windows and doors, which are comprised of both dense and sponge extruded profiles.