Rubber compounding carbon black properties

Carbon black is by far the most important filler and reinforcement agent used in rubber compounding. It is commonly used with processing oil (the black oil balance) to control the durometer hardness of the rubber compound. Carbon black is many times used with oil to reduce the cost of the compound because carbon black and process oil are usually less expensive per pound than many raw elastomers. Also, carbon black is essential for compound reinforcement, for improvement in compound physical properties such as ultimate tensile strength, abrasion, wear, and tear resistance. 

These studies have dealt with materials suitable for fuel and feedstocks, the process for converting these materials to carbon black with predictable properties, the techniques for measuring and defining those properties, a better understanding of the effects of those carbon black properties on processing parameters of compounded goods, and the predictability of the performance properties of finished rubber goods. This presentation briefly considers the status of each of these areas of study relative to today s carbon blacks and tomorrow s rubber products. 

Viscoelastic methods for the characterisation of gum rubbers are extended to rubber compounds, and the ways in which the viscoelastic properties of gum rubbers are manifested in the properties of the corresponding compounds are examined. The development of a method for evaluating strain amplification and strain rate amplification is described. Examples are presented of the characterisation of compounds with respect to variations in gum rubbers and carbon black grades, and consideration is given to the unique characteristics of compounds which are not observed in gum rubbers. Quality control tests for gum rubbers and compounds based on viscoelasticity are reviewed. 32 refs. 

Furnace carbon black is one of the most important compounding ingredients used in the rubber industry. It is certainly the most important rubber filler because it imparts such a profound improvement on cured rubber properties such as ultimate tensile strength, hardness, wear resistance, and tear resistance. Carbon black even improves the extrusion process by making the extruded rubber product smoother in appearance. By using carbon black with process oil, the rubber compound s pound-volume costs can be significantly reduced. In fact, if a rubber compound is black in color, chances are that it contains 26 to 32% carbon black. The level of carbon black... 

Fillers are used in CPE compounds for the same reasons they are used in most rubber compounds—fillers provide a means of obtaining a good balance between the necessary physical property characteristics and the economic requirements of the end-use article. The fillers used with CPE are common to the rubber industry carbon black and mineral fillers (clay, whiting, talc, silica, etc.). 

The first part of this chapter concerned the viscoelastic properties of gum rubber and how they affect those of the compound. The second part discussed the use of strain amplification as a quantitative measure of the compound characteristics, where the effect of the formulation, i.e., rubber and carbon black variation, were investigated. 

Rubber. The mbber industry consumes finely ground metallic selenium and Selenac (selenium diethyl dithiocarbamate, R. T. Vanderbilt). Both are used with natural mbber and styrene—butadiene mbber (SBR) to increase the rate of vulcanization and improve the aging and mechanical properties of sulfudess and low sulfur stocks. Selenac is also used as an accelerator in butyl mbber and as an activator for other types of accelerators, eg, thiazoles (see Rubber chemicals). Selenium compounds are useflil as antioxidants (qv), uv stabilizers, (qv), bonding agents, carbon black activators, and polymerization additives. Selenac improves the adhesion of polyester fibers to mbber. 

Above a critical hller concentration, the percolation threshold, the properties of the reinforced rubber material change drastically, because a hller-hUer network is estabhshed. This results, for example, in an overproportional increase of electrical conductivity of a carbon black-hUed compound. The continuous disruption and restorahon of this hller network upon deformation is well visible in the so-called Payne effect [20,21], as represented in Figure 29.5. It illustrates the strain-dependence of the modulus and the strain-independent contributions to the complex shear or tensUe moduli for carbon black-hlled compounds and sUica-hUed compounds. 

J.L. Leblanc and C. Barres, Bound Rubber A Key Factor in Understanding the Rheological Properties of Carbon Black Filled Rubber Compounds, Rub. Div. Mtg, ACS, Chicago, IL, April 13-16, 1999, p. 70. 

The property possessed by certain colloids of forming a gel-like structure on standing but which revert to a liquid form when subjected to agitation. The term has also been applied to the stiffening effect shown by uncured rubber compounds containing fillers, particularly carbon black. 

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