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

Kerstin Koller,Christian Paulik,Christoph Burgstaller

doi:10.1002/pls2.10061

Abstract

AbstractThe 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.

Highlights

Recycling of plastics has become increasingly important, especially as public awareness of the extent of plastic littering has grown due to photos of plastic waste floating in the oceans and media reports of microplastics in the environment
Pressure started to increase compared to the base pressure of the neat polymer, and Screen mesh size/type 100 μm/assembled
We found that contaminants which are larger than the mesh size can be filtered successfully, with the process being more effective with rigid glass beads than with softer PET particles

Summary

Introduction

Recycling of plastics has become increasingly important, especially as public awareness of the extent of plastic littering has grown due to photos of plastic waste floating in the oceans and media reports of microplastics in the environment. Recycling has to solve several critical issues: First, the plastic waste must be collected, and second it must be sorted, as different applications use different plastic materials and mixtures. 40% of the global annual plastics consumption is packaging, in which—due to its nature—plastics are used to enclose large free volumes. This makes it very material-efficient, as the packaging uses small amounts of plastic, and very visible in the waste streams. Recycling of packaging requires several steps to separate the reusable plastics from the waste stream.

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