Dielectric relaxation behavior of multiwalled carbon nanotube reinforced butyl rubber composites has been studied as a function of variation in filler in the frequency range of 20-2 Â 106 Hz. The effect of variation in filler loadings on the complex and real parts of impedance was distinctly visible, which has been explained on the basis of interfacial polarization of fillers in a heterogeneous medium and relaxation dynamics of polymer chains in the vicinity of fillers. The electric modulus formalism has been used to further investigate the conductivity and relaxation phenomenon. The frequency dependence of AC conductivity has been investigated by using Percolation theory. The phenom-enon of percolation in the composites has been discussed based on the measured changes in electric conductivity and morphology of composites at different concentrations of the filler. The percolation threshold as studied by AC conductivity occurred in the vicinity of 6-8 phr of filler loading. Scanning electron microscope microphotographs showed agglomeration of the filler above this concentration and formation of a continuous network structure.

A bifunctional silane (TESPD) was added to a vinylgroup-containing silicone rubber (SR)/natural rubber (NR)/silica compound, and the resulting mechanical, morphological, and thermal properties were compared with those of an NR/silica compound. The addition of TESPD to the silica-filled SR/NR compound formed an SR-silane-silica-silane-NR structure that behaved as a ter-polymer. The addition of SR into the NR improved the mechanical properties (torque maximum, modulus, elongation at break, and hardness) and thermal properties as well as the tan d values. The SR-silane-silica-silane-NR structure exhibited advanced properties that are suitable for an automotive engine mount application, which requires good thermal and vibration absorption properties.

The concentration effects of the silane coupling agent bis (triethoxysilylpropyl) disulfide (TESPD) on mechanical properties of silica-filled silicone rubber (SR)/natural rubber (NR) compound are investigated upon torque maximum value, tensile strength, tensile modulus and hardness. The compounds are cured with a conventional vulcanization system. The concentration range of the TESPD used is 1 to 17 phr. The optimum concentration of the TESPD is found to be 13 phr in the SR/NR compound. The degree of dispersion of silica in the rubber matrix is also examined by scanning electron microscopy (SEM).

The silane (TESPD) treated silica-filled silicone rubber (SR)/natural rubber (NR) blends are studied with regard to their mechanical, thermal, and optical properties. Two grades of SR, with and without vinyl group are used and the results are compared. The effects of a vinyl functional group in SR with respect to vibration isolation property, and mechanical properties are investigated to find maximum torque, tensile strength, tensile modulus, elongation at break, hardness and tan δ. The compounds are cured with sulfur, peroxide and peroxide/sulfur combination. The results show that the presence of the vinyl group in SR helps improve the mechanical and thermal properties of the SR/NR blend. Scanning electron microscopy (SEM) photographs show that the silica particles are well dispersed in the rubber matrix. Thermal properties including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and heat resistance are also studied. It shows the presence of the vinyl group in the SR/NR blend curing with the peroxide/sulfur combination improves both mechanical properties and the vibration properties.