Studies on Dispersion of Insoluble Sulfur in Passenger Car Radial Belt Skim Compound

Good dispersion of compounding ingredients in a rubber formulation is crucial for mechanical performance. After mixing, certain materials like sulfur, recycled materials, and zinc oxide can remain undispersed within the rubber matrix, which can lead to critical flaws and influence performance. Improper dispersion is one of the reasons for poor physico mechanical properties. The influence of temperature, mixing time and storage time of different grades of insoluble sulfur collected from one source are studied along with the standard sample of different sources. To better understand the reason for poor sulfur dispersion and high blooming, all the chemical and physical properties are analysed. The topological structures are evaluated using the thermomechanical techniques. The reason for poor dispersion and premature failure of the rubber specimen has been studied by SEM-EDS. The degradation of insoluble sulfur to soluble sulfur can be negligible during the melt mixing if the mixing is done in a controlled way. The final mixing temperature shall be maintained at 90 °C to 95 °C to restrict the insoluble to soluble sulfur conversion. This paper highlights the methodology of the development of oil-coated sulfur in rubber composites and provides insight into the dispersion of polymeric sulfur in natural rubber-based tyre carcass compounds.