Investigation of Carbon Chains in Rubber Vulcanizates by Means of Dynamic Electrical Conductivity

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Abstract
Previously obtained dynamic shear modulus data over a wide amplitude range of rubber vulcanizates loaded with carbon blacks of widely varying structure as well as graphitized black were augmented with dynamic conductivity data at 30° C and at 100° C. Results confirm the existence of reversible transient and irreversible persistent carbon structures, the former being nearly completely destroyed at moderate shear amplitudes (50% strain), but effectively restored at lower amplitudes in a dynamic equilibrium between chain destruction and reformation. Higher structure blacks are characterized by a higher rate of chain rebuilding than lower structure blacks and by marked persistent chain alignment at higher amplitudes. Conductivity as a function of strain and time shows carbon chain behavior during stressing. The rates of destruction and rebuilding of the transient chains and the exact point at which the transient structure effects balance the chain alignment effects on conductivity have been established. The unusual behavior of vulcanizates loaded with graphitized black is explained.

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