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Reinforced ethylene–propylene–diene terpolymer (EPDM) and nitrile–butadiene rubber (NBR) blends were compounded with different concentrations of azodicarbonamide (ADC/K) foaming agent to obtain foamed EPDM and NBR composites. The mechanical properties under compression and under extension at different temperatures were measured for these foams. It was found that the increase of foaming agent concentration and temperature affect all the mechanical parameters. The obtained stress–strain data are discussed in the light of the continuum mechanics theory for compressible materials.© 2002 Society of Chemical Industry

Nitrile butadiene rubber (NBR) structure foam of different apparent densities was obtained by using different concentrations of foaming agent, azodicarbonamide, ADC/K. The true stress–strain characteristics, in case of compression, of foamed samples were measured. It was found that the theoretical values predicted from the simple blending model are in more agreement with the experimental results than those from the square-relationship model. The effect of cyclic loading–unloading and dissipation energy of rubber foams was studied. The results also indicated that foams with low density exhibited a small hysteresis. The electrical properties were found dependent on the foaming agent concentration. This study was assisted by Mott and Gurney equation. The effect of compressive strain on the electrical conductivity of rubber foams was studied. The free current carrier mobility and the equilibrium concentration of charge carrier in the conduction band were produced as functions of compressive strain. The results also indicate that there is a linear variation between pressure and conductivity for all samples, which means that these samples can be used as a pressure sensor. At a certain concentration of foaming agent (7.5 phr) a change of electrical conductivity by more than three orders is observed at 20% compression strain.