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.

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).

Zinc surfactant (ZS) is added into natural rubber (NR)/silica/TESPD (bis (triethoxysilyl propyl) disulfide) and silicone rubber (SR)/NR/silica/TESPD compounds and these compounds are vulcanized. The addition of the ZS shows significant improvements on mechanical properties on both compounds. It increases the torque maximum values of the compounds as well as the tan values, which is an indirect implication that the vibration isolation property is increased. It shows the presence of zinc ion in the ZS helps silane coupling with double bond in the rubber chain. This results in improved mechanical properties such as the modulus, tensile strength, elongation at break, and hardness.