Flame-retarded halogenated unsaturated polyester resins: Thermal decomposition study

The thermal decomposition of halogenated unsaturated polyester resins (UPRs), flame retarded by zinc hydroxystannate and cross-linked with styrene, has been investigated by thermogravimetry (TG) in both dynamic and isothermal mode, and TG coupled on-line with Fourier transform infra red spectroscopy (TG-FTIR) or mass spectroscopy (TG-MS). The data from TG analysis show that degradation proceeds in two steps for pure as well as modified UPR, while the char residue at 500degreesC was considerably higher for flame-retarded resins. Analysis of the volatile decomposition products by FTIR and MS spectrocopy revealed that, during controlled heating, emission of phthalic anhydride takes place at ca. 330degreesC, then at ca. 380degreesC styrene and a complex mixture of other aromatic compounds is evolved. Further studies by TG-FTIR revealed that evolution of CO2 is considerably lowered by zinc hydroxystannate, whereas at a higher stage of decomposition evolution of H2O and HBr (traces) can be identified. On the basis of the results obtained a mechanism of decomposition was proposed that takes into account tin compounds reactions with the products coming from ester linkage rupture processes.