Role of Antiozonants in Modern Tire Compounding

The need to provide tire compounds with improved resistance to ozone has been very largely met by the use of N,N′ disubstituted-p-phenylenediamines as protective agents. These chemicals are for this reason commonly thought of as antiozonants but they also possess important antioxidant properties and in considering their role in modern compounding, it is necessary to distinguish between their antiozonant and antioxidant functions. The choice of protective system used in any particular tire component depends a good deal on the nature of the polymer. The relative behavior of natural rubber and SBR with respect to ozone cracking and flexcracking is demonstrated by data given in the paper and it is shown how a typical “antiozonant” such as isopropyl phenyl-p-phenylenediamine (IPPD) will protect SBR tread and sidewall compounds principally from static and dynamic ozone cracking and natural rubber compounds not only from ozone attack but also from various oxidative processes such as flexcracking, cut-growth and heat degradation. The effects of the partial replacement of natural rubber and SBR by polybutadiene on the antiozonant and antioxidant requirements of such tire compounds are also briefly considered.