On-Line rheometry for twin-screw extrusion (along the extruder) and its applications

Abstract

Due to a number of practical difficulties, both in- and on-line measurements of the rheological properties of complex systems during extrusion are usually performed at the end of the extruder, under very specific experimental conditions. This makes this type of instruments more useful for quality control than for process optimisation, since information about the influence of the geometry and/or processing conditions on the evolution of the material characteristics inside the extruder is not easily gathered. Recently, however, the authors have developed an on-line capillary rheometry system that overcomes most of the existing problems and allows small amounts of sample to be tested in very near real time, along the extruder. The present work aims at illustrating the usefulness of this concept for the study of physical compounding processes and some reactive systems. Two very different systems will be used for that purpose: a reactive extrusion process (the peroxideinduced thermal degradation of polypropylene) and the dispersive mixing involved in the preparation of thermoplastic/carbon fibre composites.