The nonlinear viscoelastic behavior of the composites of natural rubber filled with surface-modified nanosilica was studied with reference to silica loading. The effect of temperature on the nonlinear viscoelastic behavior has been investigated. It was observed that Payne effect becomes more pronounced at higher silica loading. The filler characteristics such as particle size, specific surface area, and the surface structural features were found to be the key parameters influencing the Payne effect. A nonlinear decrease in storage modulus with increasing strain was observed for unfilled compounds also. The results reveal that the mechanism includes the breakdown of different networks namely the filler-filler network, the weak polymer-filler network, the chemical network, and the entanglement network. The model of variable network density proposed by Maier and Goritz has been applied to explain the nonlinear behavior. The activation energy of desorption was calculated and found to be within the range of Van der Waal's interaction energy. The model fits well with the experimental results.

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Composites of natural rubber were prepared with TiO 2 and nanosilica. The stress relaxation behavior of the composites under tension was studied with reference to the filler loading and strain level. It was observed that the rate of stress relaxation increases with increase in filler loading. The rate of stress relaxation was found to be higher for silica-filled NR compared to TiO 2 -filled NR. This is due to the high degree of agglomeration in silica compared to titanium dioxide filler. The effect of ageing on the stress decay was also investigated and the rate of stress relaxation was found to decrease after ageing. The experimental curves were fitted with the stretched Kohlrausch equation. From the fitting parameters, the relaxation time and the stretching exponent were estimated in order to understand the mechanism of the relaxation processes in the filled natural rubber composites.

The mechanical and thermophysical properties of natural rubber filled with titanium dioxide (TiO2) and nanosilica composites have been investigated at room temperature for several filler concentrations. It is observed that the thermal conductivity and thermal diffusivity of the composites increase with filler loading, independent of the nature of the filler. We show that the thermal heat transport through composites is affected by the geometry of the fillers as well as the particle size and specific surface area of the fillers. The measured values of thermal conductivity have been compared to some theoretical models. The mechanical properties of the composites have also been studied and results have been correlated with thermal conductivity data.

ABSTRACT:We studied the stress-relaxation behavior of natural rubber (NR)/polystyrene (PS) blends in tension. The effects of strain level, composition, compatibilizer loading, and aging on the stress-relaxation behavior were investigated in detail. The dispersed/matrix phase morphology always showed a two-stage mechanism. On the other hand, the cocontinuos morphology showed a singlestage mechanism. The addition of a compatibilizer (NR-g-PS) into 50/50 blends changed the blend morphology to a matrix/dispersed phase structure. As a result, a two-step relaxation mechanism was found in the compatibilized blends. A three-stage mechanism was observed at very high loadings of the compatibilizer (above the critical micelle concentration), where the compatibilizer formed micelles in the continuous phase. The aged samples showed a two-stage relaxation mechanism. The rate of relaxation increased with strain levels. The aging produced interesting effects on the relaxation pattern. The rate of relaxation increased with temperature due to the degradation of the samples.

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This article aims to investigate the structure-property relationship of organoclay filled natural rubber (NR) nanocomposites. The nanostructure has been investigated by X-ray diffraction, atomic force microscopy and transmission electron microscopy. The effect of organoclay on the diffusion behavior and mechanical properties of natural rubber has been investigated. The solvent transport properties and the swelling characteristics of the nanocomposites have been studied using toluene and hexane as solvents. It is observed that the nanocomposites exhibit an anomalous trend of transport behavior. The diffusion coefficient and permeability coefficient values are found to be lower for hexane than for toluene. The nanocomposites exhibit improved mechanical properties (tensile strength, tear strength, and modulus) and hardness compared to the unfilled rubber. It is concluded that the dispersion of organoclay has a significant effect on the diffusion and mechanical properties of the nanocomposites. POLYM.

The interfacial area between the matrix and the filler is a key parameter which shapes the performance of polymer-based composites and nanocomposites, even though it is difficult to quantify. A very easy SAXS method, based on the Porod equation, is proposed for measuring the specific surface area of nanofillers embedded in a polymer matrix. In order to assess its reliability, this approach was applied to natural rubber- or styrene butadiene-based samples containing different types of montmorillonite clay. A wide range of specific surfaces was detected. SAXS data were compared to complementary X-ray diffraction and TEM information, obtaining a good agreement. Interpretation of the tensile properties by theoretical models and comparison with the literature corroborated the validity of the specific surface area measurement. The possibility to quantify this feature of composites allows the rational design of such materials to be improved.