Degradation mechanism of FKM during thermo-oxidative aging from mechanical and network structure correlations

The thermal weak point of a peroxide-cured fluoroelastomer (FKM) in presence of triallylisocyanurate (TAIC) has been identified. To that purpose, the thermal stability was assessed by TGA measurements. In parallel, thermo-oxidative degradation was characterized after the aging of several samples at 250 degrees C for various durations. Specific attention has been directed to the structural evolution, evaluated by both FTIR and equilibrium swelling experiments. Experimental results highlight that TAIC, the system's crosslink node, is the thermal weak point of a peroxide-cured fluoroelastomer (FKM). Nonetheless, crosslinks are not entirely broken since the crosslinking density decreases with aging time before stabilizing for one week at 250 degrees C. This allows the material to retain some of its mechanical properties such as good elongation at break. For longest exposure times at 250 degrees C (beyond one week), chain scission mechanism becomes predominant leading to a loss of the mechanical properties. Regarding the degradation mechanism, TGA-FTIR results are rather in favor of a dehydrofluorination mechanism as hydrogen fluoride (HF) is detected upon the first times of thermo-oxidative aging. In a second step, chain scission starts to occur. Recombination reactions between double bonds provided by dehydrofluorination and macroradicals formed during chain scission could explain that FKM is still crosslinked after one week at 250 degrees C under air.

Automated summary

A thermal weak point of peroxide-cured fluoroelastomer (FKM) in the presence of triallylisocyanurate (TAIC) was identified using TGA measurements. Thermal stability and thermo-oxidative degradation were characterized, revealing TAIC as the weak point in the FKM system. Aging at 250 degrees C led to a decrease in crosslinking density before stabilization, allowing the material to retain mechanical properties. For longer exposures, chain scission caused a loss of mechanical properties. TGA-FTIR results suggested a dehydrofluorination mechanism followed by chain scission.