Antiozonants

Antiozonants are chemical additives used to protect polymers, especially elastomeric rubbers, from ozone attack. Ozone in the atmosphere readily reacts with unsaturated polymers, causing surface cracking, crazing, and loss of mechanical integrity, particularly under tensile stress and elevated temperatures. Antiozonants work by either migrating to the surface to form a protective barrier or by reacting with ozone or its radicals, thereby reducing the amount that reaches the polymer.

Common forms include wax-based antiozonants, such as paraffin and microcrystalline waxes and wax blends, which bloom to the surface and create a protective, barrier-like layer. Other antiozonants are non-wax organic compounds, including certain amine, amide, or sulfonamide derivatives, that can scavenge ozone. In practice, antiozonants are often used in combination with antioxidants as part of an antiozonant/antioxidant package to provide surface protection against ozone as well as long-term resistance to oxidation.

Applications and considerations: Antiozonants are widely used in tires, belts, hoses, seals, and other rubber products prone to ozone exposure. Their effectiveness depends on temperature, applied stress, ozone concentration, and exposure duration. They tend to migrate to the surface and can affect appearance, gloss, or hand feel; thus formulation requires balancing protective performance with processing and aesthetic requirements. Testing for ozone resistance, such as ozone-cracking tests or standards like ASTM D1149, helps quantify performance.