Development of a method for a realistically and reproducible contamination of polymer melt filters

Abstract

In the field of polymer processing, extrusion is one of the most common processing methods. Not only in the processing of recycled materials, also when using virgin polymers there can be contaminations during the storage or processing of the material. This may adversely affect the melt quality and by this also the quality of the final extrusion product. Examples of possible contaminations are metal particles which are caused by wear and tear of the extruder, or degradation products of the processed material itself.As a result of increasing demands on the quality of extrusion products, especially in the field of fibre and film extrusion, the filtration of polymer melts is widely used and state of the art. To remove unwanted debris out of the melt, different metal filter media is used. Some examples of typical filter media are different kinds of wire mesh, filters made of nonwoven metal fibres or sintered metal powder discs. By using this filter media, it is possible to remove foreign particles like solid particles, as well as soft components, so called “gels” from the melt. This ensures a high quality extrusion result.In order to compare the filtering effect of different filter media and to assess the contamination and selective filtration, it is necessary to develop a possibility for reproducible rapid contamination of filter materials. In this work this should be elaborated as a part of the PET processing. For this, a real filter contamination is analysed. After this, a definition of an adequate substitute dirt is effected. The focus is both on solid particles, as well as on gel contamination. By this, it is possible to generate realistic and reproducible filter soiling so that pressure rise curves can be generated in order to compare the behaviour of different filter media during the extrusion process.