Antiozonant

Protective additive incorporated into rubber compounds to prevent ozone cracking — surface cracks that form perpendicular to the direction of strain when ozone (even at ambient concentrations of 25-100 ppb) attacks the carbon-carbon double bonds in unsaturated rubbers (NR, SBR, NBR). Two mechanisms: (1) Physical protection — microcrystalline waxes (1-3 phr) bloom to the surface and form a physical barrier film; effective for static applications only, as flexing breaks the wax film. (2) Chemical protection — paraphenylenediamine derivatives (6PPD, IPPD at 1-5 phr) react with ozone faster than the rubber surface, consuming ozone before it attacks the polymer; effective under both static and dynamic conditions. Both types are used together for maximum protection. Per ASTM D1149 for ozone resistance testing. Essential for any NR, SBR, or NBR product used outdoors or near ozone-generating equipment (electric motors, welding areas). EPDM, silicone, and CR have inherent ozone resistance and typically do not require antiozonant additives.