Synthesized stearyl aromatic esters, namely stearyl benzoate, distearyl phthalate, stearyl biphenyl-4-carboxylate, and stearyl naphthoate, were used as processing aids for natural rubber compounding formulations. Their effects on curing and mechanical properties of natural rubber compounds were evaluated according to ASTM D3184. It was found that the aromatic esters enhanced curing characteristics in a similar way to aromatic oil which has been typically used in otherwise similar rubber formulations. Furthermore, the aromatic esters can slightly improve mechanical properties of natural rubber vulcanizates before aging. Although the mechanical properties of the vulcanizates in terms of tear strength, compression set, and thermal stability, deteriorated with aging, most useful properties were still on levels comparable to compounds with aromatic oil. Overall, stearyl aromatic esters may potentially in the future provide environmentally friendly alternatives to the use of aromatic oil, as processing aids for the rubber industry.
