Attenuated Total Reflectance Infrared Microspectroscopy of Aged Carbon Filled Rubbers

A number of different carbon-filled rubbers have been studied using infrared microspectroscopy with an attenuated total reflectance objective incorporating a silicon internal reflectance element (IRE). Excellent spectra were obtained of these difficult samples in a reasonable measurement time. The IRE had a contact face of 100 μm diameter, but this could be apertured to improve the spatial resolution, but at the expense of the signal-to-noise ratio of the spectra. The minimum aperture size, which still produced an acceptable spectrum, was 40 μm. The spatial resolution was less than the aperture size because of the effect of the refractive index of the IRE. The method was applied to thermally aged rubbers by measuring spectra at intervals across a sectioned face. Oxidation profiles were derived from the absorbances of oxygenated functional groups in the spectra and were found to agree with those previously published. The IR-ATR microspectroscopic method is shown to be simple and effective because the measurement is made directly, and non-destructively, on the sectioned face of the rubber.