The migration of compounding ingredients to the surface of cured or uncured rubber tends to be one of the contributing factors towards the properties imparted on a rubber article such as the making of a multi-ply article like belts or tires. The effect from the migration of the compounding ingredients may or may not be detrimental to the performance of the rubber article. For instance, there are specific situations where the migration of compounding ingredients like antioxidants or waxes to the surface of a rubber compound may be beneficial to act in protecting the rubber from ozone aging. However, there are other instances where the migration of compounding ingredients harmful to the properties of the rubber compound. One of such compounding ingredients is sulfur, which can act to decrease the tackiness of rubber and hinder the formation of multi-ply articles like a tire. Therefore, there is a need to prevent the migration and formation of excess compounding ingredients like sulfur on the surface of rubber.
Microencapsulation of compounding ingredients may be used as one of the methods to prevent the migration of compounds like sulfur which was the primary area of focus. Microencapsulation of sulfur by using primarily alginate, served as the mechanism used to prevent the migration of sulfur to the surface of rubber. The microencapsulated sulfur beads produced had a number frequency distribution with 87% having a bead size less than 150 µm and the lower percentage accounting for larger bead sizes. In the 87% of the bead distribution, 44.3% accounted for bead sizes with a size range from 50 to 100 µm while 24.7% and 18.0% accounted for bead sizes with a size range from 0 to 50 µm and 100 to 150 µm respectively. The bulk of the lower percentage was in the size range from 150 to 200 µm with a value of 9.3%. Beads produced had a high percentage (> 80%) of sulfur encapsulated. These microencapsulated sulfur beads were compared with ordinary rubbermaker’s sulfur and insoluble sulfur to distinguish their effects in the compounding formulation during rubber testing. The rubber testing involved tensile study and a sulfur blooming study. The results from the sulfur blooming study suggested that microencapsulated soluble sulfur functioned better than ordinary rubbermaker’s sulfur to prevent sulfur blooming at the tested temperatures (100¿¿¿¿C and 120¿¿¿¿C). The results from the study also suggested that microencapsulated soluble sulfur performed relatively better than insoluble sulfur at the 120¿¿¿¿C temperature; however, a relatively better result was obtained for insoluble sulfur in comparison with microencapsulated soluble sulfur at the 100¿¿¿¿C temperature.
The tensile study on the other hand, indicated that both ordinary rubbermaker’s sulfur and insoluble sulfur achieved better results than microencapsulated soluble sulfur. The lower result obtained for microencapsulated sulfur was attributed to the microencapsulated soluble sulfur bead characteristics (size, shape, etc.) and the interaction of the beads in the rubber matrix. These properties might have been influential in the lower results achieved for microencapsulated soluble sulfur in addition to the crosslink density of the cured rubber compound. The results obtained from the research were useful to guide the future developments on the microencapsulation of soluble sulfur.