Search

Carbon black particulate reinforcement of rubber is examined in terms of linear viscoelasticity and the dynamics of the filler particle network. First, it is demonstrated that for the case of purely hydrodynamic reinforcement, the dynamics of the filled rubber are equivalent to those of the corresponding unfilled material. A breakdown in thermorheological simplicity is observed with the onset of filler networking in reinforced compounds. The dynamics of the filler network are initially examined by strain sweep/recovery experiments performed on uncrosslinked materials. The role of the surface activity of carbon black in defining the rate and magnitude of flocculation is explored and various models to describe this process are reviewed. The dynamics of carbon black filler networks in crosslinked materials are probed using small strain torsional creep experiments. Physical ageing (structural relaxation) of filled compounds at temperatures well above the glass transition temperature of the rubber matrix is observed and the ageing rate is found to scale with the level of filler networking in the various compounds. Physical ageing is the result of non-equilibrium, slow dynamics, which sheds light on the physical origin of the filler network. Furthermore, the implications of physical ageing of highly filled rubbers on typical linear viscoelastic time–temperature superposition experiments are discussed. [ABSTRACT FROM AUTHOR]

The strain and thermal dependence of the dynamic mechanical properties of carbon black filler networks underpin the performance of many rubber components. These effects are examined by varying the surface energetics of carbon black. This has a profound influence on the level of flocculation of the carbon black network in the final crosslinked compounds. Filler networks comprised of thermally deactivated carbon blacks are significantly more strain-sensitive - shifting the onset of the Payne effect to smaller dynamic strains. Using free vibration equipment to precisely probe the thermal sensitivity of the linear viscoelastic properties of the filled compounds, it is shown that carbon black deactivation results in carbon black networks which are more thermally sensitive than corresponding unmodified carbon black networks. Increased thermal dependence of the dynamic moduli results in the appearance of a secondary increase in tan δ as a function of increasing temperature well above the rubber Tg - which is not correlated with any thermal transitions in calorimetric experiments. Such effects are prevalent in the relevant literature for various rubber-filler combinations but their physical origins are often misinterpreted or unexplained. A rationalization of these effects based on the dynamics of the filler network is presented. [ABSTRACT FROM AUTHOR]

The process of particulate flocculation in natural rubber melts and subsequently crosslinked samples is investigated using carbon blacks of varying surface free energy, surface area and morphology. The surface free energies are varied via thermal treatment of the carbon blacks (graphitization). Reduction in surface free energy of the particulates accelerates the flocculation processes in the melt as measured by rheological experiments and reduces the percolation volume fraction threshold as determined by D/C conductivity measurements. The consequent effects on amplification of the small strain storage moduli of the crosslinked compounds are dramatic. Reduced polymer-filler interactions result in both an increased small strain modulus versus the unmodified carbon black-filled materials and an increased mechanical fragility of the fractal networks. Examination of the dynamic elastic moduli of crosslinked carbon black-filled samples loaded at volume fractions below the onset of network development reveal a significant temperature dependence isolated at the filler-rubber interface. [ABSTRACT FROM AUTHOR]