Material degradation of polypropylene on the co-rotating twin screw extruder
Final Report Abstract
As part of the previous DFG-funded project, investigations were carried out on the material degradation of polypropylene (PP) using a 28 mm twin-screw extruder. Based on the findings, recommendations for gentle processing were derived, and a mathematical model was developed to describe material degradation. The goal of the follow-up project was to evaluate the applicability of these insights to various extruder types. This included collaborative experimental investigations with industrial partners. A key focus of the project was also to study the influence of additives on material degradation. In the first phase of the project, comparative studies were conducted at KTP to assess the transferability of previous results to other machine sizes. Pure PP was processed using both 25 mm and 45 mm twin-screw extruders. The evaluation of the samples produced was based on the measurement of melt flow rate (MFR) values and their conversion to weight-average molar masses. These results aligned with earlier findings: material degradation is generally intensified by high screw speeds, low throughputs, and high melt temperatures. In parallel, experimental planning with the application partners was conducted through intensive knowledge exchange. In addition to pure PP, filled material systems were processed. A detailed study of the effect of additives on material degradation was carried out at KTP using a 28 mm twin-screw extruder. Two compounds—PP/TiO₂ and PP/CF—were investigated. Samples from both these tests and those from the application partners were analyzed using Gel Permeation Chromatography (GPC), as converting MFR to weight-average molar mass is only suitable for pure PP. The results showed that higher mechanical and thermal stress—due to high screw speeds, low throughputs, or elevated melt temperatures—leads to a greater shift of the molar mass distribution curve toward lower molar masses. This is caused by increased chain scission. After cleaning the data set by removing outliers, the degradation model developed in the previous project was globally parameterized based on the process coefficients. The result is a universally applicable model capable of predicting PP degradation across different twin-screw extruder sizes. A comparison between simulation and experimental data revealed that most test points fall within a ±20% tolerance band, indicating a satisfactory level of agreement. However, achieving sufficient correlation between simulation and measured value was not achieved for the compounds, which is due to altered degradation mechanisms of the PPs in the compound. Finally, the enhanced model was implemented into the simulation software SIGMA, developed at KTP.
Publications
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Material-Preserving Extrusion of Polyamide on a Twin-Screw Extruder. Polymers, 15(4), 1033.
Schall, Christoph; Altepeter, Matthias; Schöppner, Volker; Wanke, Sven & Kley, Marina
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Modelling of the material degradation of polypropylene on the co-rotating twin-screw extruder. AIP Conference Proceedings, 2884, 090001. AIP Publishing.
Altepeter, Matthias; Wanke, Sven & Schöppner, Volker
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Polypropylene Degradation on Co-Rotating Twin-Screw Extruders. Polymers, 15(9), 2181.
Altepeter, Matthias; Schöppner, Volker; Wanke, Sven; Austermeier, Laura; Meinheit, Philipp & Schmidt, Leon
