Service-Induced Diffusion and Nodule Formation in Rubber Stocks

Abstract

Abstract Diffusion of materials within a rubber compound caused by temperature gradients may cause nucleation and growth of crystals in favorable sites. The rubber may or may not be affected by this process, but if it is affected, a dense area termed a nodule results. Zinc stearate is the prime agent responsible for forming nodules in typical tread compounds. After the formation of a localized concentration of the stearate, crosslinking conditions are favorable and this proceeds with the infusion of sulfur. Conditions favorable to nodule formation are those conditions favoring diffusion, i.e., prime temperature gradients, “soft” compounds, solubility effects and undoubtedly dynamic mechanical stress.