Sensor-Based Sorting for Waste Plastics Recycling

An essential step in the recycling of plastic waste is the provision of a material feed suitable for the recycling processes. This concerns, e.g., both chemical and mechanical recycling. For this purpose, the waste streams, e.g., lightweight plastic packaging and shredder light fraction, must be pre-processed in a multi-stage process, typically including screening, air separation, magnetic separation, eddy current separation, and sensor-based sorting. Utilizing industrially well-established technologies, packaging material is for instance typically shredded and separated according to material groups into a metallic and plastic fraction. Furthermore, for an efficient recycling, it is often necessary to separate different polymers and thus also to be able to distinguish those. Plastic parts contained in the input material streams to be sorted can also occur in a wide variety of shapes and colors and comprise objects consisting of complex mixtures of materials and composites. During their life cycle, plastics further undergo changes in their material properties, e.g., as a result of aging. Contaminants, such as chlorinated plastics, also have a significant impact on the quality of the recycled material and must be removed during sorting. This chapter presents solutions regarding the pre-treatment processing of material streams for waste plastics recycling. The main focus lies on sensor-based sorting, as it significantly contributes to tackling the challenges mentioned above and hence achieving the desired quality of material streams for recycling due to its flexibility and programmability.