The influence of the relative molecular weight of natural rubber on its thermo‐oxidative stability

Abstract

AbstractThe influence of relative molecular weight on rubber thermo‐oxidation in air at 130 ± 1°C has been studied by means of infrared spectroscopy. The carbonyl group formation in single fractions of natural rubber has been measured. It was found that the development of kinetic curves ΔACO = f(t) corresponds for both fractionated and unfractionated extracted samples. Kinetic curves of natural rubber formation are characterized by an induction period τ. Its magnitude is a function of molecular weight up to the value [η] = 0.2 m3/kg, and then stays invariant to changes in [η]. In the range of low values of the internal viscosity up to 0.2 m3/kg, the dependence τCO = f[η] has an exponential character as a consequence of the statistical character of chains breaking down during the degradation. It has been proved that the reciprocal value dependence of the mean viscosity molecular weight of unfractionated acetone‐extracted natural rubber on the length of induction period is linear. The change in double‐bond amount during the oxidation is not reflected in the induction period determined by infrared spectroscopy.