Extrudate swell of polymer melts and compounds in various die geometries and the screw extrusion of rubber compounds

A comparative experimental and theoretical study is presented for extrudate swell and dies of various cross-sectional geometries and lengths. The geometries studied included slit, capillary, rectangular and trapezoidal dies. We also present an experimental and theoretical study of screw extrusion of rubber compounds.

The swell from slit dies is greater than the swell from capillaries. At low die wall shear rates the swell of homogeneous melts goes to a value of about 1.2 for slit dies as opposed to about 1.1 found for capillary dies.

The swell from short dies is greater than the swell from long dies. A theoretical study of extrudate swell based on unconstrained elastic recovery from poiseuille flow is developed for long dies. The argument is made that elongational flow existing in the die entry region determines extrudate swell for short dies. A theory of swell based on unconstrained recovery from the entrance flow is developed. A theory is also proposed for the swell of filled polymer melts. This involves consideration of the gel-like character of these materials.

The screw extrusion of rubber compounds has also been studied. A new model is developed which considers the slip of the rubber compounds in the region near the hopper.