FORMATION OF POLYBROMINATED DIBENZOFURANS DURING EXTRUSION OF HIGH-IMPACT POLYSTYRENE DECABROMODIPHENYL ETHER ANTIMONY(III) OXIDE

Polybrominated dibenzofurans (PBDFs) are formed during extrusion of high-impact polystyrene (HIPS) containing the flame retardant system decabromodiphenyl ether/antimony(III) oxide (Br10DPO/Sb2O3). The process of formation of PBDFs was examined at an extrusion temperature of 275-degrees-C. To get a better understanding of processes taking place in the polymer melt during extrusion, the thermal stability of polystyrene chains was also examined. It was found that the flame retardant system Br10DPO/Sb2O3 shows a stabilizing activity toward thermal degradation of polystyrene chains. Temperature development during extrusion processing of HIPS/Br10DPO/Sb2O3, simulated in a computer model, supports a mechanism of formation of PBDFs which is initiated by thermal degradation of polystyrene. Polystyrene degradation products, i.e., (poly)styrene radicals, are stabilized by radical scavenging properties of the flame retardant decabromodiphenyl ether (Br10DPO). Debromination of Br10DPO is combined with a ring-closure reaction forming PBDFs. It seems inevitable that PBDFs are formed during extrusion of polybrominated diphenyl ethers in addition polymers such as polystyrene. A tentative quantification of the yield of PBDFs in HIPS/Br10DPO/Sb2O3 by RPHPLC showed an increase from 1.5 to 9 ppm for heptabromodibenzofuran and from 4.5 to 45 ppm for octabromodibenzofuran after four extrusion cycles.