Electric, dielectric, and dynamic mechanical behavior of carbon black/styrene‐butadiene‐styrene composites

The conductivity of styrene‐butadiene‐styrene block copolymers containing different amounts of extraconductive carbon black (CB) was investigated as a function of the mold temperature. The composites exhibited reduced percolation thresholds (between 1.0 and 2.0 vol % CB). The dynamic mechanical analysis characterization revealed that the glass‐rubber‐transition temperatures of both segments were not affected by the CB addition, although the damping of the polybutadiene phase displayed a progressive drop with an increase in the CB concentration. The normalized curves of tan δ/tan δmax (where tan δ represents the value of the loss tangent at any measurement temperature and tan δmax represents the loss tangent peak value at the corresponding temperature Tmax) versus T/Tmax (where T is the temperature and Tmax is the maximum temperature), corresponding to both polystyrene and polybutadiene phases as well as the activation energy related to the glass‐rubber‐transition process, did not present any significant change with the addition of CB. The dielectric analysis revealed the presence of two relaxation peaks in the composite containing 1.5 vol % CB, the magnitude of which was strongly influenced by the frequency, being attributed to interfacial Maxwell‐Wagner‐Sillars relaxations caused by the presence of different interfaces in the composite. The mechanical properties were not affected by the presence of CB at concentrations of up to 2.5 vol %.