Effects of thermal aging on degradation mechanism of flame retardant-filled ethylene-propylene-diene termonomer compounds

Ethylene-propylene-diene termonomer (EPDM) compounds filled with halogenated (Br and Cl) flame retardants (FRs) and Sb₂O₃ were prepared via melt mixing, and their thermal stability, weight loss, and elemental composition were investigated as a function of aging conditions (temperature: 120-380°C, period: ~100 h, and atmosphere: nitrogen and air). The thermal aging was done with thermogravimetic analysis under both isothermal and nonisothermal conditions and a convection oven. Scanning electron microscopy-energy dispersive spectroscopy was used to study the surface morphology and elemental composition of the thermally aged FRs-filled EPDM compounds. For a better precision of compositional analysis, a laser-induced breakdown spectroscopy (LIBS) was employed in this study. The thermal degradation behavior of EPDM compounds containing halogenated FRs was strongly dependent on the aging atmosphere (N₂ or air) and type of FRs. The weight loss of the EPDM compounds during thermal aging was found to be quite small in the temperature ranges below 190°C, while it was noticeable above the temperature. The LIBS technique can be an effective and promising analysis tools for analyzing the elemental components in a bulk rubber compound. Two possible mechanisms were proposed for the thermal degradation of the EPDM compounds containing brominated FR and Sb₂O₃.