Conception of a measuring methodology for the degradation behavior of polypropylene and polystyrene in the extrusion process

点击翻译按钮获取中文摘要

In the field of polymer processing, polymers are plasticized in order to be able to process them into end products or semi-finished products. The processing of polymers is often carried out on screw machines. Examples are extruders and injection moulding machines. During processing on such screw machines, the material is subjected to high thermal and mechanical stress. This load can lead to a change in the properties of the material in the form of a molecular mass degradation. This molecular mass degradation can also lead to changes in the mechanical and chemical properties of the polymer.The degradation of the molecular mass was investigated in detail in the preceding DFG project for polypropylene (PP) and polystyrene (PS). In this case, the material degradation was converted into a mathematical model, which enables the calculation of material degradation caused by processing. The modeling is based on three degradation parameters, which have to be known for each material: the residence time sensitivity, the shear rate sensitivity and the temperature sensitivity. These parameters have to be determined by laboratory test series and a subsequent regression for each material type. Experimental investigations have shown that a type-related determination of the material parameters is not sufficient. Even when looking at several types of polypropylene, the sensitivities in terms of residence time, temperature and shear rate are not identical. This is presumably due to a different stabilization of the different material types. Therefore it is necessary to determine the material characteristics for each individual material in order to enable an adequate calculation of the material degradation. Since the determination of these parameters is very time-consuming, it is currently not economical for the calculation of material degradation. The aim of this research project is to develop a possibility for the fast measurement of the required material sensitivities. This should be done in cooperation with the company KAUTEX Maschinenbau GmbH. The test method to be developed should ideally enable to determine the degradation parameters within a few hours. This would significantly increase the applicability of mathematical calculation.In the first step, suitable measuring methods for determining the required material parameters have to be selected based on the previous project. Also their usability needs to be tested. Based on this, a measurement methodology is to be developed which will initially enable a fast and reliable determination of the material degradation parameters. This measurement concept should be transferred into a prototype. The measurement results will be validated on the basis of experimental data and the applicability of the measurement methodology to other materials will be tested.