Mixing on Melting in Single Screw Extrusion

Abstract

Abstract A new approach to assessing mixing in single screw plasticating extruders is proposed. It is based on image analysis of microtomed sections obtained from the polymer helix formed in a suddenly cooled split barrel extruder fed with a mixture of black and white polymer granules. The observations suggest that most of the mixing occurs on melting with little improvement thereafter. A simple laminar mixing model is drawn in the melting zone the results of which compare favourably with experimental data. In particular, it is shown that improved mixing can be achieved with increasing screw speed in complete contradiction with the classical strain theories which consider mixing in the melt conveying zone only.