Investigation of Rheological, Mechanical, and Viscoelastic Properties of Silica-Filled SSBR and BR Model Compounds

Active fillers such as carbon black and silica are added to rubber to improve its mechanical and viscoelastic properties. These fillers cause reinforcement in rubber compounds through physical and/or chemical interactions. Consequently, the compounds’ rheological, mechanical, and viscoelastic behavior are affected. Changing the filler loading influences these properties due to the different interactions (filler-filler and filler-polymer) taking place in the compounds. In addition, rubbers with varying microstructures can interact differently with fillers, and the presence of polymer functionalization to enhance interactions with fillers can further add to the complexity of the network. In this work, the effects of different loadings (0–108 phr/0–25 vol. %) of a highly dispersible grade of silica with three types of solution styrene-butadiene rubbers (SSBR) and one butadiene rubber (BR) on their rheological, mechanical, and viscoelastic properties were investigated. It was observed that the Mooney viscosity and hardness of the compounds increased with an increasing filler loading due to the increasing stiffness of the compounds. Payne effect measurements on uncured compounds provided information about the breakdown of the filler-filler network and the extent of the percolation threshold (15–17.5 vol. %) in all the compounds. At high filler loadings, the properties for BR compounds worsened as compared to SSBR compounds due to weak polymer-filler interaction (strong filler-filler interaction and the lower compatibility of BR with silica). The quasi-static mechanical properties increased with the filler loading and then decreased, thus indicating an optimum filler loading. In strain sweeps on cured rubber compounds by dynamic shear measurements, it was observed that the type of rubber, the filler loading, and the temperature had significant influences on the number of glassy rubber bridges in the filler network and, thus, a consequential effect on the load-bearing capacity and energy dissipation of the rubber compounds.