Thermo-oxidative ageing of a SBR rubber: effects on mechanical and chemical properties

In this work, the effects of thermo-oxidative ageing at different temperatures and for different exposure durations on the mechanical and the chemical properties of a styrene butadiene rubber (SBR) are presented. Uniaxial tensile tests, hardness measurements, Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) spectra analysis, and swelling tests are carried out on as-received and aged samples. Accelerated ageing process was conducted at different temperatures ( 50^∘ C , 70^∘ C , 90^∘ C , and 100^∘ C ) and for different exposure durations (7, 14, 21, 28, 35, 45 and 60 days).This work confirm that accelerated ageing lead to a decrease of the ultimate mechanical properties and of the molar mass between cross-links in one hand, and an increase of the cross-linking density and of the material hardness, in another hand. ATR-FTIR analysis shows significant changes in the chemical structure of aged SBR samples dominated by the thermo-oxidative process, which is, mainly pronounced at high temperature and long exposure time. The ultimate mechanical properties are related to the average molar mass between cross-links. A threshold value of this property corresponding to a complete degradation of the rubber can be determined. Finally, the time–temperature equivalence principle is applied to build master curves describing the evolution of certain quantities such as molar mass between crosslinks, tensile strength, and strain at break versus the reduced time. A predictive modeling of the stress and strain at break as function of the effective ageing time is proposed which give satisfactory results.