Evaluation of the External Surface Area of Carbon Black by Nitrogen Adsorption

Specific surface area is an important property for carbon black grade classification, production control, and prediction of rubber reinforcement characteristics. Total surface area alone is insufficient for estimating the reinforcing properties of a microporous carbon black because the internal area of the micropores is inaccessible to rubber molecules. The CTAB surface area test, based on adsorption of a molecule too large to enter the micropore, measures the surface area available to rubber. Although widely used, the CTAB method has failed to gain wide popularity due to its labor-intensive nature and poor testing precision. In the present paper, the extent of microporosity on the surface of carbon blacks is investigated. The external surface area derived from the nitrogen adsorption characteristics is compared to CTAB surface area for a number of standard rubber carbon blacks. This study reports the optimum testing conditions to achieve precise external surface area measurements and the ability of this method to overcome the disadvantages of the CTAB method. Other advantages of this technique are discussed.