The polymer composite material filled with piezoelectric ceramic particles and electroconductive particles is a damping material, which has a new damping mechanism. In addition to this new mechanism, this composite has conventional damping properties due to the viscoelasticity of polymer and the interparticle-friction of fillers. The new damping mechanism, called “the piezoelectric damping effect”, is due to piezoelectricity and consumptive circuits in the composite material. Mechanical vibration energy, transmitted to piezoelectric particles, is converted into electric energy by piezoelectric effect is converted into Joule′s heat through the conduction paths between electroconductive particles. In this study the relationship between the damping performance and the elastic modulus of this composite was discussed. The piezoelectric effect of this damper relates to the effectiency of vibration-transmission in the composite material. The elastic modulus and the damping performance of the composite material were measured as a function of piezoelectric particle sizes. As a result of increasing the elastic modulus, total damping performances are decreased, but the contribution of the piezoelectric damping effect is increased and the other viscoelastic and interparticle-friction effects are decreased. These phenomena can be explained qualitatively with the dispersion model in two-phase composite materials.

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The grafting reactions of diene rubbers, such as NR, BR, and SBR, with surface radicals formed by the decomposition of azo groups introduced onto carbon black or calcium carbonate were investigated. The introduction of azo groups onto carbon black surface was achieved by the reaction of isocyanate groups with 4, 4-azobis (4-cyanopentanoic acid) (ACPA). Azo groups were also successfully introduced by the reaction of 12-hydroxystearate-modified calcium carbonate with ACPA. Even if untreated carbon black and calcium carbonate was heated with dine rubbers, no grafting of these rubbers onto these surfaces was observed. On the contrary, by the heating of carbon black or calcium carbonate having azo groups with rubbers in toluene, the corresponding rubbers were successfully grafted onto these surfaces: the percentage of grafting of NR, BR, and SBR onto carbon black was determined to be 35.8, 41.8, and 38.8%, respectively. The percentage of grafting of rubber onto carbon black increased with increasing reaction temperature, but no grafting proceeded at 25°C because of the small decomposition rate of azo groups. These results indicate that surface radicals formed by the thermal decomposition of azo groups on the surface react with double bonds of rubbers. The percentage of BR grafting onto carbon black and calcium carbonate increased by the addition of styrene monomer in the reaction mixture. It was found that rubber-grafted carbon black gave a stable colloidal dispersion in a good solvent of grafted rubber.

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Failure criterion of carbon black reinforced rubbers is investigated in the deformation modes of uniaxial and biaxial extension experiments. The biaxial extension is applied on rubber specimen by a balloon method. It was found that the criterion is represented the “maximum strain theory”. This criterion was found to be applicable to pure vulcanizates by S. kawabata before and the investigation presenting here has confirmed that this criterion is valid to also carbon black reinforced rubber. The derivative of the strain energy density function, ∂W/∂I₁, is increased by the reinforcement and, therefore, the breaking stress is increased by the reinforcement remarkably especially in the equal biaxial extension mode because of the failure behavior expressed by the maximum strain theory.

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