Modelling of material degradation of polypropylene on the co-rotating twin screw extruder

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The degradation of plastics during the processing process affects the properties of the final product. By mechanical and thermal stress during the process, polymer chains are broken down or degraded by oxidative degradation. Reduced fracture properties of the end product can be the result, among other things. However, the degradation of material can only be determined after the compounding process, which entails a great amount of money and time. The aim of this project is the development of a model for the description of molecular weight degradation in the processing of polypropylene on the co-rotating twin-screw extruder. The aim is to develop a process that is as gentle as possible, but which nevertheless takes into account additional boundary conditions, such as a high throughput. The parameters shear rate, residence time and temperature should be taken into account as influencing parameters for the model. By varying the screw and temperature configuration as well as different speeds and throughputs, the mentioned influencing parameters are to be varied. For the present project, polypropylene is to be used as a plastic to be examined, since this represents one of the industrially most important bulk plastics. Three different PP types are used, which differ in terms of the MFI. The target value to be investigated is the intrinsic viscosity. Using empirically determined parameters representing the hydrodynamic interactions between polymer coil and the solvent, the Mark-Houwink plot describes the proportional relationship between the intrinsic viscosity and the molecular weight (viscosity average). The determination of the intrinsic viscosity should be done by means of an Ubbelohde viscometer. By comparing the transit time of the solvent and the solution with a certain concentration, the relative viscosity is described. By the approach of Billmeyer the Staudinger index can now be determined. The evaluation method of gel permeation chromatography is not used in this case because the economic outlay is disproportionate to the benefit and the measurement of the intrinsic viscosity is easier for the later application. Selected operating points are still examined by gel permeation chromatography to verify the model. The experimental investigations and their evaluation serve to develop a new model for the description of material degradation during processing on twin-screw extruders.