Investigation on the thermal oxidative aging mechanism and lifetime prediction of butyl rubber

Accelerated thermal aging experiments were conducted on butyl rubber materials in order to investigate aging behavior using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), positron annihilation lifetime spectroscopy (PALS), and differential scanning calometry (DSC). The XPS results suggested that the thermal oxidation process took place heterogeneously along the samples thicknesses. The aging mechanism was identified to be crosslinking by means of the combined use of PALS and DSC results. Lifetime and intensity of ortho-positronium (o-ps) diminished, and the glass transition temperature (T (g) ) increased during aging. The dispersion condition of silica particles, observed by SEM images, showed that the filler agglomerated after aging. Time temperature superposition was carried out using compression set measurements in the temperature range of 100 to 60 A degrees C. The Arrhenius plot clearly exhibited a curvature around 75 A degrees C, and the activation energy dropped from 126.7 to 58.8 kJ/mol across this region. Relative importance of different processes, over the entire temperature range, was discussed; lifetime at room temperature was predicted.