ROLE OF MORPHOLOGY AND STRUCTURE OF CARBON-BLACKS IN ELECTRICAL CONDUCTANCE OF VULCANIZATES

Results of an experimental study are presented which show that the low electrical resistance of vulcanizates loaded with conductive carbon blacks in a given particle size range is caused 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. 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. 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.