Influence of material contamination on polypropylene melt filtration using assembled and fused screens

The large range of polymers produced leads to their use in such diverse areas as packaging, the automotive industry, electrical applications, electronics, household appliances, building, and construction. For these applications, materials should be clean and free from contaminants, such as unintentionally cross-linked material (gels), unconverted polymers, agglomerated additives, dirt, and dust. Since 2000, the amount of plastic produced globally has increased by 5% per year. In 2019, Europe consumed 50.7 million tonnes of plastics, and demand is increasing. As production rises, so does waste, making it essential to reduce plastic waste via recycling. To be recycled, materials must be clean and free from contaminants. While numerous preparation processes in recycling can reduce contamination, the final remaining contaminants can be separated from the polymer by melt filtration. The aim of this work was thus to gain insights into the mechanisms underlying melt filtration in an extruder to determine how effective the process is depending on the type of contamination (PET particles and glass beads served as model contaminants). Additionally, behavior and filtration efficiency of two different screen-pack types were investigated. We found that rigid contaminants (i.e., glass beads) can be filtered from the melt by using screens that are finer than the particle size, but removing soft contaminants, (i.e., PET particles) requires even finer.