Processability and viscoelastic properties of natural rubber (NR) compounds filled with different carbon black loadings and types were investigated with the use of a steady shear rheometer, namely, the Mooney viscometer, and an oscillatory rheometer, namely, the Rubber Process Analyser (RPA2000). It was found that the type and amount of carbon black strongly influence the viscoelastic properties of rubber compounds. Both the dilution effect and filler transient network are responsible for the viscoelastic properties, depending on the vulcanization state. In the case of uncured compounds, the damping factor of the uncured NR decreases with increasing black loading. This is attributed to the reduction of mobilized rubber content in the compound (or the dilution effect). However, in the case of the cured NR vulcanizates, the filler transient network is the dominant factor governing the damping factor of the vulcanizate. With increasing black loading, the damping factor of the vulcanizate clearly increases.
Two-layered vulcanisates were prepared from two rubbers with different dynamic properties, and the bulk dynamic properties of the layered rubber vulcanisates were assessed. The results reveal that the bulk dynamic properties are strongly dependent on a layer thickness ratio. For the specimens in which each layer has similar compressive modulus and dynamic properties, the relationship between the bulk dynamic properties and the layer thickness ratio obeys a rule of mixture. However, for the specimens in which each layer has a large difference in compressive modulus, some deviation from the rule of mixture towards the layer with relatively large deformability (i.e., the layer with relatively low compressive modulus) is observed.
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