Observations on the thermogravimetric oxidation of carbon blacks in vulcanizates

Abstract Thermogravimetric oxidation under isothermal conditions of carbon black residues from styrene—butadiene rubber vulcanizates was investigated as a method of identification of carbon black type. Although a relationship has been reported between the rate of oxidation and the surface area of the carbon black, we have found that this relationship holds only for some carbon blacks significantly separated in surface area. Further, we have found that the rate of oxidation can be quite different for the same type of carbon black produced by different manufacturers, and that the rate of oxidation of the carbon black residue from the pyrolyzed vulcanizate can depend on the procedure used for mixing and vulcanizing the rubber compound. This technique, therefore, cannot be recommended as generally suitable for identification of carbon black type in an unknown vulcanizate. The isothermal oxidation technique used in conjunction with the derivative thermogram has been found to be useful in determining the amount of carbon black in carbonizing elastomers such as chloroprene and nitrile rubbers.