Gamma irradiation in multi-cycle ABS recycling- effects on ABS properties and the recovery of antimony

Licentiate thesis, 2013

Electronic waste, also called waste electrical and electronic equipment (WEEE), is the fastest growing waste stream in Europe today. The fast exchange pace of mobile phones, televisions and computers creates an important need to develop recycling areas to take care of, reuse and recycle these materials. Metals and plastics are equally important to recover from the waste, especially to fulfil the European Directives on the minimum amount of reused and recycled material. In order to facilitate the recycling, this project has looked into the possibilities of leaching antimony (Sb) with various weak acids from one of the main plastic constituents in electrical and electronic equipment (EEE): acrylonitrile butadiene styrene (ABS). Sb is a synergist to brominated flame retardants and a hazardous substance. The influence of gamma-irradiation on ABS has been investigated in a series of experiments. Firstly the hypothesis that irradiation would have a beneficial effect on the recycling of the plastics by re-extrusion, the plastic was also aged by heating it in an oven (90 oC, 144 h). Secondly the effect of irradiation on the rheological properties such as viscosity was investigated. Thirdly, the influence of irradiation on the leaching of the antimony from the plastic was studied. The main results show that antimony can be leached from ABS by heated sodium hydrogen tartrate in dimethyl sulfoxide (DMSO) with an estimated efficiency of 50 %. Gamma-irradiation has an impact on the mechanical and rheological properties of ABS. The yield stress increased with irradiation doses of 0, 10, 50 and 400 kGy. The viscosity also increased in the test samples with irradiation doses of 0, 10, 100 and 200 kGy. In the multi-recycling and accelerated aging test there was a significant reduction in stiffness for the gamma-irradiated samples after the second out of four cycles which is not fully understood. There was no ductile to brittle transition noticed with respect to the strain rate. Keywords: ABS, WEEE, gamma-irradiation, recycling, antimony, plastics