Studies on the Mechanism of Thermal Decomposition of Unsaturated Polyester Resins with Reduced Flammability

Abstract

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 by 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 unmodified as well as modified UPR, but the char residue at 500°C was considerably higher for flame-retarded resins. Analysis of the volatile decomposition products by FT-IR and MS spectrocopy revealed that during controlled heating, the emission of phthalic anhydride takes place at ca. 330°C, followed by styrene at ca. 380°C., and a complex mixture of other aromatic compounds are evolved. Further studies by TG-FTIR revealed that evolution of CO2 is considerably lowered by zinc hydroxystannate, andat a later stage of decomposition the 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 the reaction of tin compounds with the products of ester linkage rupture processes.