Wax Protection

Abstract

Abstract Wax migrates from the bulk of a rubber article to its surface to form a physical barrier to ozone attack. The extent of migration depends upon the solubility/mobility characteristics of the specific wax under a given set of environmental conditions. Factors which influence migration include time and temperature of storage after cure, wax concentration, wax composition, and amount and type of filler and extender oil present. This makes it difficult to select a wax which performs effectively over a broad temperature range. Paraffinic waxes generally protect better at low exposure temperatures, while microcrystalline waxes are more effective at elevated temperatures. Wax blends offer a wider temperature range of protection. An optimum migration temperature exists for each wax, and DTA can predict this optimum. Best ozone resistance is also attained at the temperature corresponding to optimum wax migration. Under dynamic ozone conditions, waxes alone can be harmful. Addition of a chemical antidegradant is required to obtain protection under these conditions.