A novel process for the removal of bromine from styrene polymers containing brominated flame retardant

High-impact polystyrene (HIPS) is one of the main plastic fractions of waste electric and electronic equipment (WEEE). Although recycling of this material is desirable, the presence of brominated flame retardants requires the removal of bromine prior to further treatment steps in order to avoid deterioration. In this study, a new method was developed for the removal of bromine from the polymer without destroying the polymer matrix. Organic bromine from the flame retardant (decabromodiphenyl ethane) was converted into inorganic bromide using a solution of NaOH in ethylene glycol (NaOH(EG)). Using a stirred flask as the reaction vessel, a debromination ratio of 42% was obtained at 190 °C regardless of the NaOH concentration. The same reaction in a ball mill reactor reduced the bromine content in the HIPS to 0.02 wt%. The conversion of organic bromine into inorganic bromide reached 98%. Degradation products from the flame retardant were identified using high performance liquid chromatography coupled with mass spectrometry. In both the flask and ball mill reactor, the reaction was diffusion controlled with an activation energy of about 205 kJ mol−1. The thermal stability of the residual plastic was enhanced during the treatment, which opens up the possibility of reusing waste HIPS by mechanical recycling.