Furthering the understanding of the non linear response of filler reinforced elastomers

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The cyclic deformation of filler reinforced elastomer compounds results in energy losses caused by a partial hysteretic breakup and subsequent reformation of the filler network. This phenomenon has significant socio-economic consequences as it affects the rolling resistance of tires and consequently the fuel economy of cars. The results of experiments with an on line rheometer provide more detail on our earlier reported findings that this filler network does not exist after the elastomer compounds are first mixed but forms on storage by a flocculation process particularly at higher temperatures to which rubber compounds are exposed to during shaping and vulcanization. Additionally they suggest that the formation of a filler network does not only depend on the type and volume fraction of filler but also on the thermodynamic interaction between the host polymer and the polymer chains which attach themselves physically and/or chemically to the filler surface during composite mixing. Since the embedded fillers resemble core/shell nanoparticles we drew on the results of published theoretical studies on the stabilization of colloidal systems to help define key factors contributing to the stability and equilibrium morphology of filler reinforced elastomers. The insight gained offers an explanation on why composites made with end group functionalized polymers have a reduced filler network manifested by a significantly lower excess storage modulus ΔG′.