Relationship between conductivity and stress–strain curve of electroconductive composite with SBR or polycaprolactone matrices

• The measurement on materials exhibiting yielding were first time described.
• Attributing each part of stress–strain curve to electrical conductivity changes.
• Attributing the physical filler network structure to stress stain curve shape.
• For elastomeric and thermoplastic matrices similar features have been found.

Electroconductive composites were prepared using either elastomeric (styrene–butadiene rubber) or thermoplastic (polycaprolactone) matrix with varying amounts of two grades of electroconductive carbon black. For all composites, electrical conductivity was measured during rising deformation and at the same time a stress–strain curve was recorded. The changes in electrical conductivity during deformation were not monotonic, and several extremes were observed. From a comparison of the mechanical and electrical responses of the materials, a decrease in the conductivity was observed at the beginning of deformation in the Hookean elastic region. At a deformation near the yield point for the thermoplastic matrix and near the inflection point for the elastomeric matrix, the increase in conductivity was observed, followed by a decrease in conductivity in the region of plastic flow. All effects of conductivity changes were interpreted in terms of either the destruction or the formation of new conductive pathways formed by the filler. The changes in the structure of reinforcing carbon blacks may be a general process for other filler materials, including nonconductive reinforcing fillers. Thus, electrical conductivity may be correlated with the specific features of the physical network of the reinforcing filler that affect the mechanical properties of the composite.

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