Sorting mixed polymers from end of life products by a selective grinding process

Abstract

European policy on waste and market demand for material are driving the development of sorting techniques adapted to automobiles and electric products at the end of their lifetimes. In this article, we present work on polymer sorting using selective grinding. Selective grinding is an operation that consists in sorting polymers after shredding. Specific particle size distributions characterize each polymer in the output stream and these differences are used to recover certain polymers by sifting. This process is based on the brittle or ductile properties of polymers. The first results presented in this work concern the sorting of a mixture of polymers and polyolefins, which are chemically incompatible. The working method adopted includes three parts. In the first part, a stream of mixed polymers from the shredder residue (SR) of a treatment chain was characterized. The mixed stream was composed of different grades of Polypropylene and different grades of Polyethylene. Afterwards, based on the characterization data, selective grinding tests were carried out on a model mixture with virgin materials. Once the selective grinding conditions were validated, other tests were carried out with shredder residues. The conclusion of this study is that selective grinding can be an efficient technology to sort incompatible polymers, which are not sorted by other processes, such as density separation or automated near infrared sorting.