Modelling the contamination behaviour 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, but also when using virgin polymers, contaminations can occur 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.As a result of the increasing demands on the quality of extrusion products, especially in the field of fiber 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 are used. Some examples of typical filter media are different kinds of wire mesh, filters made of nonwoven metal fibers 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 calculate the lifetime of a filter in an extrusion process, a new possibility of modelling the filter contamination is presented in this work as a part of the PET processing. At first, a method for reproducible rapid contamination of filter materials was developed in pre-investigations. After this, a high number of experimental investigations have been done in order to generate a wide data basis for the modelling of the filter contamination. This soiling behavior is then mathematically modelled, in that manner that the filter lifetime can be calculated.