The Role of Morphology and Structure of Carbon Blacks in the Electrical Conductance of Vulcanizates

Abstract The low electrical resistance of vulcanizates loaded with conductive carbon blacks in a given particle size range is cause by the low density of the particles, high structure, or both. In addition, the smaller the particle size of the black, the lower the resistivity. The same factors also cause high modulus and, in liquid dispersions, high viscosity. It is shown that acetylene black owes its lower resistivity in vulcanizates to its high structure. Vulcan XC 72 owes its even lower resistivity to both high structure and low particle density, while EC Black owes its lowest resisitivity to an extremely low particle density caused by the presence of a large number of hollow-shell particles, as indicated by electron micrography. It was shown that the resistivity of vulcanizates loaded with EC Black is practically unaffected by deformation up to 150%, in contrast to other conductive blacks at comparable resistivities. It has been observed that increasing the degree of loading leads to a lower limit of resistivity, about equal for all of the blacks. The various phenomena could be explained by the concept that the resistivity of carbon black loaded vulcanizates resides in the gaps between particles or aggregates and is determined by a process of electron tunneling.