Electro-mechanical properties of conductive epoxy composites

The electrical resistivity of epoxy composites was studied during curing and heating of the cured material. The initial resistivity ρ of epoxy containing a metallic filler was in the range of 10 6 to 10 7 Ωcm. During curing a sudden reduction of ρ by eight orders of magnitude was observed. The shrinkage of the polymer during cross-linking and the build-up of internal stresses results in a lower inter-particle contact resistance. The contraction can be reversed by heating up again. Around the curing temperature, the resistivity increased by six to eight orders of magnitude due to the expansion of the material. The resistivity increased progressively until the contacts between the particles were opened and the composite reached a high-ohmic state.