Full definition
Antiozonants are protective additives specifically designed to prevent ozone cracking in rubber compounds. These surface cracks occur when ozone molecules attack the carbon-carbon double bonds found in unsaturated rubbers such as Natural Rubber (NR), Styrene-Butadiene Rubber (SBR), and Nitrile Butadiene Rubber (NBR). Ozone, even at low ambient concentrations of 25-100 parts per billion (ppb), can lead to significant damage, particularly in outdoor applications or environments near ozone-generating machinery like electric motors and welding equipment. Antiozonants work primarily through two mechanisms: physical protection and chemical protection. The former utilizes microcrystalline waxes, typically in concentrations of 1-3 parts per hundred rubber (phr), which migrate to the surface to form a protective film. However, this method is limited to static applications since the film can be disrupted by flexing or movement of the rubber component.
On the other hand, chemical protection involves the incorporation of paraphenylenediamine derivatives, such as 6PPD and IPPD, in the range of 1-5 phr. These compounds react with ozone more rapidly than the rubber itself, effectively consuming the ozone before it can initiate damage to the polymer chains. This dual approach—combining both physical and chemical antiozonants—ensures maximum protection against ozone degradation, allowing the rubber to maintain its performance and integrity over time. The effectiveness of antiozonants in rubber formulations is often evaluated according to ASTM D1149, a standard test method for ozone resistance in rubber, which helps manufacturers determine the longevity and durability of their rubber products in ozone-rich environments. Notably, rubbers such as EPDM, silicone, and chloroprene (CR) possess inherent ozone resistance and usually do not require additional antiozonant additives, making them suitable for various outdoor and industrial applications.