The Life Cycle Engineering research group of SIM² – KU Leuven has investigated the effectiveness of density-based sorting processes for separating recyclable plastics used in electronics and cars. For this research, the group worked together with Galloo and Ad Rem, two Flemish companies active in the field of sorting and recycling. With the use of spectroscopic characterisation techniques and lab-scale density-separation experiments, it was possible to assess the capabilities of density-based sorting processes and to indicate the optimal use of this type of sorting techniques for separating post-consumer plastic fractions. The results of the research were summarised in the article “Evaluating the effectiveness of density-based sorting of plastics from WEEE and ELVs”, published in the journal “Resources, Conservation & Recycling”.

In many state-of-the-art sorting companies, density-based sorting is applied to separate several groups of metals and plastics by density. In the investigated instance, plastic waste was separated with this technique in three fractions: one fraction going to landfill, one incinerated for energy recovery and one recycled fraction. Samples were collected from each of these fractions to assess their composition with two spectroscopic characterization techniques: Fourier-Transfrom Infrared (FTIR) and X-Ray Fluorescence (XRF). Using FTIR measurements, the polymer types in the investigated fractions could be identified, while the concentrations of concerning substances such as bromine and chlorine could be measured using XRF. A high number of samples could be characterised by using a custom-made automated system for the two types of measurements. In total, more than 10 000 measurements were performed for this research.

By performing lab-scale density measurements prior to the spectroscopic characterisation, the polymer type concentrations and bromine and chlorine levels could be analysed in function of density, which offered valuable insights to optimise the used density-based sorting techniques. Furthermore, comments on the planned changes to the EU restrictions of some brominated flame retardants in recycled plastics could be made based on the outcomes of the experiments. Excessive tightening of the allowed levels of some restricted flame retardants could have a strong negative effect on the volumes of plastics that can be recycled.

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