ANALYTICAL INVESTIGATION OF WAX MIGRATION IN RUBBER COMPOUNDS

Migration of wax in a model sidewall formulation was studied by characterization of the compound surface over time. Vulcanizates were prepared with different wax types at equal loadings, including neat paraffinic wax, a 1:1 blend of paraffinic and microcrystalline wax, and neat microcrystalline wax. The amount of wax on the surface was measured by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and was governed by the type of wax included in the formulation. The ATR-FTIR findings were corroborated by the performance of each vulcanizate under ozone aging at static conditions. Despite the distinct differences observed in the quantity of surface wax, gas chromatography (GC) analysis of the surface waxes indicated that the composition of the migrated wax was remarkably similar regardless of the wax type used. Additionally, the degree of similarity between the composition of the constituent wax and wax recovered from the surface film correlated directly with film thickness. These results provide observable evidence in support of the theory that wax migration is governed by the competing effects of solubility and mobility of alkane chains within the rubber matrix and demonstrate a framework for future investigations of rubber oxidation mitigation. The combination of ATR-FTIR and GC, in particular, permits identification of specific wax fractions migrating out of the rubber matrix and quantification of the corresponding film thickness over an extended period of time, resulting in a robust characterization of the compound surface and thorough understanding of optimal wax compositions for various implementations under isothermal, application-specific conditions.