Thermal conductivity of EPDM rubber composites as a function of filler concentration and type.

Abstract

Thermal conductivities of EPDM (ethylene propylene diene monomer) rubber loaded with one of the following fillers: carbon black type N339, a reinforcing filler, kaolin, a non-reinforcing filler, and ground charcoal have been studied using a guarded hot plate apparatus designed at Kenyatta University. The hardness and tensile strength as well as the breaking energy of the composites have also been determined. The results show that the thermal conductivity, increases with increasing filler concentration in the composites. The thermal conductivity values also increase with increasing composite hardness. Thermal conductivity and tensile strength values were higher for the composites filled with reinforcing filler than those filled with non-reinforcing ones. The high values are explained in terms of the filler-polymer interaction energies that are higher in composite filled with reinforcing fillers than those filled with the non-reinforcing ones. Using several known thermal conductivity models, for bi component composites, the theoretical values of thermal conductivity were calculated for the various filler concentrations and compared with the experimentally determined values. None of these models, successfully predicted the experimental values of thermal conductivity of rubber composites. In almost all the cases the theoretical values of k for kaolin, charcoal and carbon black samples are at variance with the experimental values. Explanation for this discrepancy is based on the fact that the polymer filler interaction-parameter which is different in the three fillers used plays an important role in facilitating thermal conductivity in the composites. Besides other results, the conductivity-hardness and tensile strength results confirm this observation. As a major finding of this work, it is observed that the theoretical models available have been derived on the basis of conductivities of the individual components, they do not incorporate the interaction parameter which apparently plays an important role in rubber composites.