Electronic Waste Plastics Characterisation and Recycling by Melt-processing

University dissertation from Chalmers University of Technology

Abstract: Melt-processing of blended plastics from waste electrical and electronic equipment (WEEE) is a method to facilitate mechanical recycling, and this might improve the recycling conditions and increase the amounts of plastics being recycled. To ensure the quality of melt-blended plastic waste, it is essential to know the composition of the incoming material and then possibly improve the compatibility between the different polymer phases. WEEE plastic compositions as well as the mechanical and thermal properties obtainable from a model material of a recyclable WEEE plastics blend have been studied in this work. A real collected and recyclable WEEE plastics fraction was found to contain mainly high impact polystyrene (HIPS, 42 weight% (wt%)), acrylonitrile-butadiene-styrene copolymer (ABS, 38 wt%) and polypropylene (PP, 10 wt%). The remaining part (10 wt%) consisted primarily of other styrene-based thermoplastics and polyolefins. 1-2 wt% were found to be non-thermoplastic contaminants including wood, polyurethane foam and silicone rubber. The amount of merged HIPS and ABS was relatively stable at 80 ± 4 wt% (95% confidence interval) in the sampled waste volume of 600 kg. Virgin and recycled (containing real collected and sorted WEEE plastics) ternary blends, with the same relative composition of HIPS, ABS and PP as presented above, were blended to model the studied WEEE plastics fraction. Melt-processing by extrusion was compared with injection moulding. An intermediate degree of orientation corresponding to 400-500 % melt-elongation, obtained by extrusion, resulted in the highest ductility while the ductility of the injection-moulded material was significantly lower, but exhibited less variation. The stiffness and yield stress of the recycled ternary blend were found to be higher, while the elongation at break was lower than the values for the virgin blend. It was also seen that the stiffness and the yield stress of the virgin and recycled blends mainly followed the rule of mixtures, but that blending had an adverse impact on the elongation at break, indicating incompatibility between HIPS, ABS and PP. The thermal analysis of the blends indicated relatively low thermo-oxidative stability, with an onset temperature of exothermic oxidation at 187 oC for the recycled blend and 200 oC for the virgin blend. The low thermo-oxidative stability indicated that it is necessary to increase the amount of active thermo-oxidative stabilisers. The low ductility of the blends implied the need of improving the compatibility between the plastic phases.

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