Analysis and modelling of the material degradation of polypropylene on the co-rotating twin-screw extruder

During compounding on co-rotating twin-screw extruders, the properties of a base polymer are specifically modified by blending in additives or other polymers. Besides the desired effect of melting and mixing, an undesired, mostly irreversible material degradation occurs during the compounding process. The resulting changes in the molecular structure influence the rheological properties of the polymer melt during processing and the mechanical properties of the final product. In this work, the material degradation of polypropylene on the co-rotating twin-screw extruder was experimentally investigated and modelled. It was found that high rotational speeds, low throughputs and high melt temperatures increase material degradation. Compared to these factors, the screw configuration has a rather small influence on the degradation behaviour. For the mathematical description of the material degradation, a model for single-screw extruders developed in a previous research project at Kunststofftechnik Paderborn (KTP) was modified. Since the model provides a good prediction of the material degradation of polypropylene on the twin-screw extruder, it was implemented in the SIGMA simulation software.