Adherent and slippery walls for extrusion of entangled polymer melts and compounds

A brief overview is given of the distortions observed when polymer melts or compounds are extruded. It appears that extrusion through steel dies can be done either with macroscopic slip or with no‐slip wall conditions. Recent experimental and theoretical progress made in understanding the various aspects of slip at the wall, and its measurement techniques, are presented. Boundary conditions for rubber compounds flowing through steel‐walled dies could be seen to be much more complex than those for melts. However many aspects of the methodologies developed are of common interest both for melts and rubber. It has already been suggested that advantages can be obtained from the use of slippery walls in extrusion. Such wall properties have already been used indeed for a long time with compounds, where processing additives are introduced. New experimental data are presented concerning two typical EPDM compounds series, obtained using several laboratory techniques at the same time. Constitutive equations for the bulk and for friction at the wall can be introduced at present and adjusted to experimental data. Die extrusion can be simulated numerically, and significant improvements can be expected in quality and productivity.