Twin screw extruders are mostly used for the processing of plastics. Technical applications are, for example, the incorporation of fillers and reinforcing materials or the mixing of plastics with each other. An important process characteristic is the stressing of the material and the associated material degradation. In addition to mixing and melting, the thermal and mechanical stress in the compounding process leads to mechanisms that cause a shortening of the molecular chains of the plastic and consequently lead to a decrease in the average molecular weight. This material degradation causes a change in the chemical structure and influences the flow properties during processing and the mechanical properties of the subsequent end product. It is particularly critical that the decrease in the mechanical properties of polypropylene is mostly irreversible. From the investigations on the material degradation of polypropylene in the twin-screw extruder at the Institute of Plastics Technology in Paderborn, recommendations for action result on how the material degradation can be optimised in practice. First it was demonstrated that reproducible material degradation of polypropylene during processing in the twin-screw extruder is possible before the influences of the various process parameters were detected. In a full factorial experimental design, throughput, screw speed, temperature profile and screw configuration were varied in combination with two types of polypropylene. In summary, material degradation can be reduced by lowering the speed, increasing the throughput, reducing the barrel temperature or adjusting the screw configuration. However, when varying the operating parameters, the influence on other quality parameters such as melt homogeneity must always be taken into account. Furthermore, the developed calculation model for the material degradation of polypropylene, which was implemented in the simulation software SIGMA, is presented.