Correlation between (nano)-mechanical and chemical changes occurring during photo-oxidation of filled vulcanised styrene butadiene rubber (SBR)

Abstract

Photo-oxidation at λ > 290 nm was performed on vulcanised styrene butadiene rubber (SBR) designed for flooring applications. The effect of the presence of coated titanium dioxide (TiO2), used as a pigment, was evaluated. The chemical and nano-mechanical changes occurring at the surface during irradiation were studied by micro-FTIR spectroscopy and atomic force microscopy (AFM). Both techniques were used to obtain the oxidation profiles in the depth of the composites (in the absence and presence of TiO2) to characterise the oxidative layer formation. The nano-mechanical and chemical profiles were superimposed for both composites (SBR and SBR/TiO2) suggesting a correlation between both properties. Indeed, the increase of the DMT modulus determined by AFM reflects the crosslinking reactions which occur simultaneously with the formation of oxidised photo-products.Moreover, during irradiation, the mechanical properties were followed at low and high degree of deformation by means of dynamic mechanical analysis (DMA) and tensile test until break, respectively. We demonstrate that the physico-chemical properties of the oxidised layer which represents 20 μm of the 600 μm of the material can explain the loss of mechanical properties for both composites based on vulcanised SBR and SBR/TiO2 during irradiation at λ > 290 nm. We also demonstrate a different mechanical behaviour in presence of TiO2 compared to neat SBR that could be due to a competition between formation of photo-products and the filler-rubber debonding during photo-oxidation.