Toward recycling ʺunsortableʺ post-consumer WEEE stream: Characterization and impact of electron beam irradiation on mechanical properties

Abstract

The work reported here is the first study aimed at providing a full screening of a real unsortable non-recycled post-consumer WEEE stream free of brominated flame retarded plastics, separated using on-line X-ray detection, toward its recycling. In the existing sorting lines, up to 40% of plastics from waste electrical and electronic equipment (WEEE) stream can be rejected, herein named unsortable plastics. To have the most representative homogeneous sample for physico-chemical characterizations, a sampling method was developed to overcome the heterogeneity of the investigated 500 kg batch. The batch screening on both representative samples (∼500 μm size) and 100 plastic fractions (∼20 mm size), by means of routine techniques used in the plastic industry, has allowed to quantify reliably the main polymers included in the studied batch; ∼50% styrene-based polymers, ∼15% polypropylene (PP), ∼15% polycarbonate (PC), ∼1–4% polyamide (PA), polyethylene (PE), polyvinyl chloride (PVC), poly (ethylene terephthalate) (PET), poly (methyl methacrylate) (PMMA) and ∼8% of multi-layer plastics, paints and thermosets. The identification of the ∼8.0% inorganic phase by X-ray fluorescence spectrometry revealed the presence of several additives/charges commonly incorporated in plastic materials, such as calcium carbonate and talc. The studied batch was then subjected to electron beam irradiation at 50 and 200 kGy doses, as a means of compatibilization between the batch components. The mechanical properties and thermal behavior of irradiated samples pointed out the crucial role of the residual free radical scavenger agents present in post-consumer WEEE streams, leading to significantly different properties compared to those of irradiated virgin polymer blends highlighted in the literature.