The term dynamic properties as applied to elastomers refers to the response to periodic or transient forces which do not cause failure or appreciable fatigue (permanent change of properties) during the investigation. Generally this is limited to vulcanizates subjected to deformations not exceeding about 25%; and generally the dynamic properties are measured after several cycles or (in a transient experiment such as resilience) after several preconditioning transients, so that the Mullins effect or difference between first and second strain cycles is not of consequence. Thus, dynamic properties represent the viscoelastic properties of vulcanizates at deformations below about 25%, after reaching a pseudo-equilibrium state. The dynamic properties of rubber are altered tremendously by the addition of a filler. The scope of this article is restricted to the dynamic properties of rubber vulcanizates with carbon black as a filler. The effect covered in this article are important in designing rubber compounds to be used under dynamic conditions, such as tires, power transmission belts, vibration isolation mountings, etc. However, the engineering application of dynamic properties, which has been treated in detail elsewhere, is outside the scope of this review. A certain amount of background material is needed. We will first define the terms used in describing dynamic properties. The methods and instruments used for measuring these properties will be described briefly, and the nature of carbon black will be reviewed. Finally, some historical material is given, together with the dynamic behavior of typical compounds, as a preface to the review of more recent work in this field.

Electrical conductivity is important in many rubber and plastic compounds including antistatic applications, wire and cable sheathing, and shielding against electromagnetic interference (EMI). Elastomers and plastics are insulators (dielectrics) to which conductivity is imparted by addition of a finely divided or colloidal filler of high intrinsic conductivity, such as carbon black. Over the years, there has developed a sizable body of information regarding measurement of conductivity, and the factors which affect it in such compounds or composites. With regard to the physical processes involved in the conduction of electricity, various mechanisms have been proposed by various authors. It appears that many physical processes can be involved and that the dominant process depends upon the composition of the composite and the conditions of measurement. The purpose of this review is to survey the proposed mechanisms of conduction in composites of carbon black and nonconductive polymers, taking special note of recent theoretical advances, and to examine the effects of the properties of the carbon black and the composition of the composite.

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The most highly reinforcing fillers, namely carbon blacks and silicas, consist of aggregates of quasi-spherical particles fused together. In the absence of direct experimental studies with single-particle carbon blacks or silicas of high surface area, we cannot be sure if aggregated structure is essential for good reinforcement, or whether aggregation and fusion just happen to accompany the formation of fine particles at practical concentrations. In any case, there is no doubt that the aggregate nature of the filler plays a major role in determining the properties of the rubber compound. Here I would like to review what we know about filler aggregates, especially of carbon black, and suggest some mechanisms for their effects on rubber; and also indicate where our knowledge seems inadequate at the present time.