Effects of Wax and Substituted p-Phenylenediamine Antiozonants in Rubber

Abstract

Abstract Wax was found to reduce fatigue life and dynamic ozone resistance. These losses can be partially compensated for by the addition of a substituted paraphenylenediamine (PPD). An increase in PPD concentration leads to a slight increase in wax bloom. At low levels of wax (1 phr), this effect will lead to a significant increase in static ozone protection. A critical level of wax bloom is required to form a continuous film for optimum static ozone protection. The relative increase in ozone protection provided by a wax/PPD combination was similar for both an NR tread and an NR/BR sidewall formulation. The amount of wax bloom was much higher in the NR/BR compound compared to the NR stock. In both cases, however, the critical level of wax bloom was exceeded; thus, a significant difference in static ozone protection is not expected. At practical levels of antiozonant, no synergism between wax and PPD was observed in static or dynamic ozone exposure tests. Significant synergism was observed under intermittent test conditions. This is due to a combination of the effective static ozone protection of the wax with the dynamic protection of the PPD.