Dynamic properties of carbon black filled elastomers containing liquids.
This thesis examines the reinforcing mechanisms of carbon black fillers on an elastomer matrix. Principally the dynamic mechanical behaviour of engineering elastomer compounds is investigated. These compounds contain a range of values for both the level of reinforcing carbon black filler and the amount of liquid that has been incorporated over a range of temperatures.
A free vibration technique was adopted to measure both the small oscillation dynamic storage and loss moduli for a range of elastomer compounds over a range of specified tensile pre-strains. It was observed that the dynamic properties of carbon black filled elastomers without an incorporated liquid were independent of the static pre-strain at low extensions. A combination of finite extensibility and strain amplification effects could be used to explain the increase of dynamic storage and dynamic loss moduli with the amount of carbon black loading at higher pre-strains. An increase in the temperature caused a dramatic reduction in both the storage and loss moduli, and the relaxation processes were accelerated.
A range of different liquid oils was incorporated into the filled elastomer compounds to investigate their effect on the dynamic mechanical properties. It was noted that the incorporation of the liquid into the material before vulcanisation affects the curing process and results in compounds of an unknown cross link density. To compensate for this the liquids were mostly incorporated by a post vulcanisation swelling process. The liquids produced a relatively large decrease in both the storage and loss moduli when compared with the corresponding changes in unfilled elastomer. These decreases can be at least approximately ascribed to a combination of the softening effects of swelling on the rubber matrix and the decrease, with swelling, in the effective volume fraction of filler.
To further understand the filler reinforcing mechanisms, electrical conductivity experiments were undertaken. These experiments suggest that the filler structure is broken down on initial loading, and that this structure does not reform on unloading as has been proposed in the past.