Mechanisms of thermal degradation of a polyester flame-retarded with antimony oxide brominated polycarbonate studied by temperature-programmed analytical pyrolysis

Thermal degradation of a flame-retarded poly(butylene terephthalate) (FR-PBT) consisting of PET and a synergistic flame-retardant system based on brominated polycarbonate (Br-PC) and Sb2O3 was studied by means of various temperature-programmed analytical pyrolysis techniques such as temperature-programmed pyrolysis-mass spectrometry (TPPy-MS), TPPy-atomic emission detection (TPPy-AED) and TPPy-gas chromatography (TPPy-GC). During the degradation of FR-PBT, brominated phenols were first observed to evolve at temperatures slightly lower than those for the flammable product evolution from the substrate polymer (PBT), followed by the evolution of HBr over the whole range of degradation temperatures for the substrate polymer. These degradation processes were closely related to the synergistic effects of Sb2O3 on the decomposition of Pr-PC in the flame-retardant system to promote the thermal degradation of Pr-PC at lower temperatures than those for pure Pr-PC. Furthermore, the evolution of the flame poisoning SbBr3 formed through the reaction between Br-PC and Sb2O3 could also be monitored directly by TPPy techniques. On the basis of the data obtained by these TPPy techniques, the thermal degradation of the FR-PBT and synergistic flame-retarding mechanisms are discussed. (C) 1998 Elsevier Science Limited. All rights reserved.