Reinforcement effects in fractal-structure-filled rubber

A quantitative morphological analysis has been performed using AFM and SAXS measurements in order to determine the spatial distribution of fillers in silica SBR composites. The proportion of fillers in agglomerates or aggregates of silica has thus been separated. Additional measurements have been carried out to quantify the amount of modified polymer in the vicinity of the filler surface, i.e. the bound rubber. It is shown that the reinforcing phase, constituting both silica particles and bound rubber, can be considered either as the dispersed or the continuous phase depending on the filler content.The linear dynamic mechanical properties of composites are then analysed. The variations of the shear modulus as a function of the filler content are then related to either the reinforcement effect induced by fillers or the development of specific additional interactions between phases, i.e. the interface effects. To separate the respective contribution of these effects from the overall dynamic behaviour of composites, micromechanical modelling is then performed. In a first step, the viscoelasticity of composites reinforced by 5.7 vol% of silica is predicted with the help of Christensen and Lo's model. For composites filled with 10 and 15 vol% of silica, self-consistent modelling, applied in a reverse mode, confirmed that the reinforcing phase, i.e. silica particles and bound rubber, acts as the continuous phase, in agreement with the morphological analysis. From the predicted dynamic mechanical properties of the reinforcing phase, the bound rubber behaviour is thus extracted as a function of the filler content and compared to that of unfilled SBR.