Electrical, Thermal and Mechanical Properties of Epoxy Composites with Carbon Micro- and Nanofillers

The electrical, thermal, and mechanical properties of epoxy composites with different types of carbon fillers: colloidal graphite (CGr), carbon black (CB), as well as carbon nanotubes (CNTs) and thermally expanded graphite (TEG) have been investigated. Measurements of surface and volume electrical resistivity of the samples were carried out at room temperature.It was established that the electrical conductivity of the composites exhibits a percolation behavior and strongly depends on the morphology and concentration of the fillers. It was shown that composites filled with carbon black are characterized by electrical resistivity lower by several orders of magnitude compared to composites with colloidal graphite at the same filler content (10-20 wt. %), which is explained by the formation of a continuous conductive cluster at lower filler concentrations. The addition of 1-2 wt. % of carbon nanotubes or thermally expanded graphite along with CGr or CB particles reduces the electrical resistivity of the composites by 1-2 orders of magnitude due to a synergistic effect between the particles of the basic carbon filler (CGr or CB) and the nanoscale fillers during the formation of a continuous electrically conductive cluster. The incorporation of 10-20 wt. % of carbon black into the epoxy matrix (also in combination with nanocarbon fillers, CNTs or porous TEG), leads to a significant increase in the electrical conductivity of the composites. It was shown that, unlike electrical conductivity, the thermal conductivity of epoxy composites with carbon fillers, colloidal graphite or carbon black, changes slightly and varies within (0.25-0.55 W/(mK)) depending on the type and content of the carbon filler.Load-strain diagrams of carbon-epoxy composite samples under uniaxial compression up to failure were studied. An increase in the effective Young’s modulus with increasing content of the basic filler (CGr or CB) and its decrease upon the introduction of nanofillers (CNTs or TEG) were established. The obtained results indicate the potential of the studied materials with thermal insulation properties for use in functional protective systems.