Chapter 5 - Analysis of polymer melt flow

Abstract

This chapter describes the analysis of polymer melt flow. It is fundamental to the operation of all of the major melt processing techniques for thermoplastics. It begins by explaining the general behaviour of polymer melts and demonstrates the importance of experimentally derived flow curves for the understanding of processing behaviour. It then develops relationships for isothermal flow of Newtonian fluids in uniform channels and shows how rheological models may be used to represent polymer melt flow. This enables the analysis to be deepened to include the flow of non-Newtonian fluids in non-uniform channels. Consideration is also given to the elastic behaviour of polymer melts and the prediction of die swell due to shear and tensile stresses. The chapter includes descriptions and basic analysis of the major experimental methods used to obtain flow data. The remainder of the chapter consists of a series of illustrative example problems in which detailed analysis of melt flow behaviour in processing operations such as extrusion, injection moulding and blow moulding is presented. This includes the introduction of basic heat transfer analysis for the consideration of conduction and convection during processing.