Thermo-chemical recycling of plastics retrieved from waste electric and electronic equipment (WEEE) by pyrolysis: Identification of the polymer type, removal of bromine compounds from plastics based on an environmentally-friendly process and characterization of the pyrolysates

Abstract

The increased amounts of plastics originating from waste electric and electronic equipment (WEEE) necessitates finding environmentally friendly solutions for their handling. Taking into account the importance of the aforementioned issue, in this work attention is paid to the recycling of various plastic materials coming from WEEE. Plastic samples including parts from televisions, computers, printers, remote controls and a calculator, were collected from a recycling plant and from end-of-life household appliances. After collection and size reduction, they were analysed by various techniques, including Fourier transform Infra-Red spectroscopy (FTIR) measurements, for the identification of the polymers present in each device, since they were unknown. Their degradation behaviour was investigated via Evolved Gas Analysis (EGA), by heating them from 100 to 700 °C. Thermal pyrolysis was applied with the aim of recovering the monomers or secondary useful products during the samples’ degradation. X-ray fluorescence (XRF) analysis was applied to all samples collected in order to identify the possible presence of bromine, in case those plastics were brominated flame retarded; and it was found that 41% (7/17) of the samples contained bromine. The brominated samples were subjected to Soxhlet extraction aiming to reduce the bromine incorporated into them. Results showed that bromine was reduced in all cases tested, reaching up to 35% reduction. According to EGA analysis, the thermal degradation in most cases followed a one-step mechanism. FTIR and thermal pyrolysis results revealed that most samples consisted of high-impact polystyrene (HIPS), while some of them were blends of polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) or ABS. The chemical recycling of the samples, via pyrolysis, led to monomers (e.g., styrene), or other valuable compounds, including hydrocarbons or phenols, depending on the type of the polymer present in each sample.