Effect of flame-retardant structure on high impact polystyrene

Abstract

Flame retardant high impact polystyrene (HIPS) was prepared using several brominated flame retardants. These were decabromodiphenyl oxide (DE 83-R), octabromodiphenyl oxide (DE 79), tetrabromobisphenol A (BA 59) and polydibromostyrene (PBDS-80). In order to raise limiting oxygen index (LOI) from 18.8 of the base HIPS resin to 25 which is at V-0 rating, antimony trioxide (Sb₂O₃) as the synergist and chlorinated polyethylene (CPE) as dripping inhibitor were added. These materials were mixed in a single screw extruder. All the 36 blends composed of HIPS resin and other materials, i.e., brominated flame retardant 12, 13.5 and 15 phr, antimony trioxide 3, 4 and 5 phr and chlorinated polyethylene 10 phr or none. They were cut into pellets and then subject to injection molding as the specimens for physical and mechanical testing including LOI measurement. It was found that each flame retardant can be mixed with antimony trioxide and chlorinated polyethylene at different proportions to enable the most suitable formular which provides LOI of 25 and the highest Izod impact strength with the least amount of the flame retardant. They are as followed: DE 83-R 13.5 phr, Sb₂O34 phr and CPE 10 phr; DE 79 13.5 phr, Sb₂O₃ 5 phr and CPE 10 phr; BA 59 15 phr, Sb₂O₃ 4 phr and CPE 10 phr; PBDS-80 15 phr, Sb₂O₃ 4 phr, CPE 10 phr. The results indicate that the molecular structure of the flame retardant had influence on the ignition resistance and the other properties of the blends. Among these four brominated flame retardants, DE 83-R would provide the best formulation of flame retardant HIPS according to the properties of the blend which was influenced by the molecular structure of DE 83-R.