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Filler reinforced rubber is widely used for engineering applications; therefore, a sound characterization of the effects of physical aging is crucial for accurately predicting its viscoelastic properties within its operational temperature range. Here, the torsion pendulum is used to monitor the evolution of the storage and loss modulus of carbon black filled samples for four days after a temperature drop to 30   ° C . The storage modulus presents a continuous increase, while the loss modulus generally displays a steady decrease throughout the four days that each test was conducted. The relationship of the recovery rates with the carbon black properties is also studied, analysing its dependency on the particle size and aggregate structure. The evolution of the recovery rate seems to depend linearly on the surface area while the carbon black structure appears to have a much weaker influence on the physical aging behavior for the set of compounds tested. The obtained results corroborate the presence of physical aging at room temperature for filler rubber materials and the ability of the torsion pendulum to monitor the storage and loss modulus change, providing pivotal data on the influence of physical aging on the viscoelastic properties of the material. [ABSTRACT FROM AUTHOR]

The Payne Effect (also known as the Fletcher–Gent Effect) has a fundamental impact on the behavior of filled rubber composites and therefore must be considered during their design. This study investigates the influence of carbon black (CB) surface area and structure on the observed Payne Effect and builds on the existing models of Kraus and Ulmer to explain this phenomenon. Dynamic strain sweeps were carried out on natural rubber (NR) compounds containing eight different grades of CB at equivalent volume fractions. The loss and storage moduli were modeled according to the Kraus and Ulmer equations, using a curve optimization tool in SciPy. Subsequent regression analysis provided strong correlations between the fitting parameters and the CB structure and surface area. Using this regression analysis, this work provides further insight into the physical meaning behind the Kraus and Ulmer models, which are phenomenological in nature. [ABSTRACT FROM AUTHOR]

The influence of carbon black (CB) structure and surface area on key rubber properties such as monotonic stress-strain, cyclic stress–strain, and dynamic mechanical behaviors are investigated in this paper. Natural rubber compounds containing eight different CBs were examined at equivalent particulate volume fractions. The CBs varied in their surface area and structure properties according to a wide experimental design space, allowing robust correlations to the experimental data sets to be extracted. Carbon black structure plays a dominant role in defining the monotonic stress–strain properties (e.g., secant moduli) of the compounds. In line with the previous literature, this is primarily due to strain amplification and occluded rubber mechanisms. For cyclic stress–strain properties, which include the Mullins effect and cyclic softening, the observed mechanical hysteresis is strongly correlated with carbon black structure, which implies that hysteretic energy dissipation at medium to large strain values is isolated in the rubber matrix and arises due to matrix overstrain effects. Under small to medium dynamic strain conditions, classical strain dependence of viscoelastic moduli is observed (the Payne effect), the magnitude of which varies dramatically and systematically depending on the colloidal properties of the CB. At low strain amplitudes, both CB structure and surface area are positively correlated to the complex moduli. Beyond ~2% strain amplitude the effect of surface area vanishes, while structure plays an increasing and eventually dominant role in defining the complex modulus. This transition in colloidal correlations reflects the transition in stiffening mechanisms from flexing of rigid percolated particle networks at low strains to strain amplification at medium to high strains. By rescaling the dynamic mechanical data sets to peak dynamic stress and peak strain energy density, the influence of CB colloidal properties on compound hysteresis under strain, stress, and strain energy density control can be estimated. This has considerable significance for materials selection in rubber product development. [ABSTRACT FROM AUTHOR]

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]

The introduction of dynamic bonds capable of mediating self-healing in a fully cross-linked polychloroprene network can only occur if the reversible moieties are carried by the cross-linker itself or within the main polymer backbone. Conventional cross-linking is not suitable for such a purpose. In the present work, a method to develop a self-healable and recyclable polychloroprene rubber is presented. Dynamic disulfide bonds are introduced as part of the structure of a crosslinker (liquid polysulfide polymer, Thiokol LP3) coupled to the polymer backbone via thermally initiated thiol-ene reaction. The curing and kinetic parameters were determined by isothermal differential scanning calorimetry and by moving die rheometer analysis; tensile testing was carried to compare the tensile strength of cured compound, healed compounds and recycled compounds, while chemical analysis was conducted by surface X-ray Photoelectron Spectroscopy. Three formulations with increasing concentrations of Thiokol LP-3 were studied (2, 4, 6 phr), reaching a maximum ultimate tensile strength of 22.4 MPa and ultimate tensile strain of 16.2 with 2 phr of Thiokol LP-3, 11.7 MPa and 10.7 strain with 4 phr and 5.6 MPa and 7.3 strain with 6 phr. The best healing efficiencies were obtained after 24 h of healing at 80 °C, increasing with the concentration of Thiokol LP-3, reaching maximum values of 4.5% 4.4% 13.4% with 2 phr, 4 phr and 6 phr, respectively, while the highest recycling efficiency was obtained with 4 phr of Thiokol LP-3, reaching 11.2%. [ABSTRACT FROM AUTHOR]

Modelling the viscoelastic behavior of rubber for use in component design remains a challenge. Most of the literature does not consider the typical regimes encountered by anti-vibration devices that are deformed to medium dynamic strains (0.5 to 3.5) at medium strain rates (0.5/s to 10/s). Previous studies have either focused on the behaviour at small strains and small strain rates or in fast loading conditions that result in low cycle fatigue or tearing phenomena. There is a lack of understanding of the dynamic response of natural rubber suspension components when used in real vehicle applications. This paper presents a review of popular viscoelastic nonlinear constitutive models and their ability to model the mechanical behaviour of typical elastomer materials such as Natural Rubber (NR) incorporating different PHR (Parts per Hundred Rubber, XX) of carbon black. The range of strain and strain rate are typical for the materials used in rubber suspensions when operating in severe service operating conditions, such as over rough terrain or over pot-holes. The cyclic strain is applied at different amplitudes and different strain rates in this medium strain range. Despite the availability of many models in the literature, our study reports that none of the existing models can fit the data satisfactorily over a wide range of conditions. [ABSTRACT FROM AUTHOR]

The nature of filler-polymer and filler-filler interactions in rubber composites under strain remains an open question in soft matter physics. These interactions are key to explaining the rich variety of complex behavior exhibited by particle-filled rubber products. In this paper we demonstrate a simultaneous dielectric/dynamic mechanical analysis technique (SDMS) which provides new insights into the structure-property relationships of filled rubbers. The complex permittivity of carbon black filled natural rubber has been characterized under a simultaneous tensile strain field (from 0.1% to 50%). The complex permittivity exhibits a dramatic nonlinear dependence on strain coupled with features which are analogous to mechanical strain softening and strain history, namely the "Payne" and "Mullins" effects. The sensitivity of the complex permittivity to such effects is several orders of magnitude greater than in corresponding, traditional mechanical tests. In addition, we demonstrate for the first time that it is possible to use both strain and electrical field frequency as "dipole filters" which can be used to selectively probe the dipoles present at the polymer-filler interface. [ABSTRACT FROM AUTHOR]