Enhancing Performance of Silica-Filled Isoprene Rubber: The Synergistic Role of Urea and Silane Coupling Agent

This study investigated the compatibility between silica and synthetic polyisoprene rubber (IR) by examining the synergistic effects of urea and silane (Si-75) as coupling agents. Comparative analyses were conducted on synthetic IR formulations containing silica: without silane (Si-75), with silane alone, and with a combination of silane (Si-75) and urea. The results revealed that the presence of urea alongside silane reduced both cure and scorch times while increasing maximum and delta torques. These findings suggest an enhanced interaction between synthetic IR and the amine groups of urea on the silica surface. Furthermore, the combination of urea and Si-75 enhanced the 100% and 300% modulus, as well as the tensile strength of vulcanized IR. Analyses of the Payne effect, cross-link density, and FTIR confirmed a more effective distribution of silica within the IR matrix. Scanning electron microscopy characterization revealed smaller silica agglomerates in the IR/silane/urea system. Dynamic mechanical analysis provided a comprehensive evaluation, corroborating that urea, in conjunction with silane, facilitates optimal silica dispersion in the IR.