THE INFLUENCE OF THE POLYMER MATRIX ON THE FORMATION OF POLYBROMINATED DIBENZO-PARA-DIOXINS (PBDDS) AND POLYBROMINATED DIBENZOFURANS (PBDFS)

During micro-pyrolysis of polybrominated diphenylethers (PBDPOs), which are used as flame retardants in synthetic polymer blends, PBDDs and PBDFs are formed. The yield decreases from Br5DPO --> Br8DPO --> Br10DPO due to the energetically favourable elimination of HBr. The influence of the high impact polystyrene (HIPS) polymer matrix on the formation consists of a selectivity towards formation of PBDFs, a shift in the optimal PBDF formation temperature from T = 600-degrees-C to the HIPS depolymerisation temperature T = 350-400-degrees-C and an enhancement of the total yield of PBDFs with a factor 7. The key towards understanding of the low PBDF formation temperature lies in the fact that PBDPOs are incorporated in a polymer matrix. During radical depolymerisation of the HIPS polymer matrix PBDFs are formed by the exchange of hydrogen and bromine which is followed by a ring closure reaction. The thermal degradation processes of HIPS/Br10DPO/Sb2O3 were studied dynamically with in-source temperature resolved Py-MS (negative ions). Several processes taking place during degradation of the HIPS/Br10DPO/Sb2O3 polymer matrix, like debromination of the flame retardant Br10DPO to form less brominated diphenylethers, formation of PBDFs, bromination of polystyrene and formation of antimony (oxy)bromides, were elucidated with this technique.