Structure in Carbon Blacks

It is well known that the tensile strength of carbon black filled hydrocarbon rubbers increases with black structure at elevated temperatures, but not at room temperature or below (175). Since primary structure in carbon black increases modulus, hysteresis, and stress-softening (Section VII), an increase of the strength with structure might be expected on consideration of Eq. (32). The conditions under which tensile strength becomes independent of carbon black structure correspond to the regime... 

Breuer, O., Tchoudakov, R., Narkis, M., and Siegmann, A. (1997) Segregated structures in carbon black-containing immiscible polymer blends HIPS/ LLDPE systems. J. Appl. Polym. Sri., 64, 1097. 

Kluppel M, Heinrich G. Fractal structures in carbon black reinforced rubbers. Rubber Chem Technol 1995 68 623-51. 

Kluppel M and Heinrich G (1995) Fractal Structures in Carbon Black Reinforced Rubbers, Rubber Chem Techno/68 623-651. 

K.M. Jager, D.H. McQueen. Fractal structures in carbon black polymer composites. Third International Conference on Carbon Black, Mulhouse, France, Oct. 2000, 117-120. 

Carbon blacks are synthetic materials which essentially contain carbon as the main element. The structure of carbon black is similar to graphite (hexagonal rings of carbon forming large sheets), but its structure is tridimensional and less ordered. The layers of carbon blacks are parallel to each other but not arranged in order, usually forming concentric inner layers (turbostratic structure). Some typical properties are density 1.7-1.9 g/cm pH of water suspension 2-8 primary particle size 14-250 nm oil absorption 50-300 g/100 g specific surface area 7-560 m /g. 

Equations 22.3-22.14 represent the simplest formulation of filled phantom polymer networks. Clearly, specific features of the fractal filler structures of carbon black, etc., are totally neglected. However, the model uses chain variables R(i) directly. It assumes the chains are Gaussian the cross-links and filler particles are placed in position randomly and instantaneously and are thereafter permanent. Additionally, constraints arising from entanglements and packing effects can be introduced using the mean field approach of harmonic tube constraints [15]. 

Figure 16. Electron micrographs showing floe structure of carbon black dispersed in odorless kerosene after 150 hours of agitation. Parts OLOA-1200 per 100 parts of carbon black (a)-0, (b)-0.A, (c)-2.0, (d)-A.O. These are from samples (a), (c), (i) and (k) of Figure 15. Reproduced with permission from Ref. (1A). Copyright 1983, Elsevier Science Publishers.

The word particle has become so widely used in the technical rubber and carbon black hterature that it is convenient to retain the term when in fact nodule is meant. The layer planes are curved, distorted, and of varying size. They also intersect and interconnect one particle or nodule with its neighbors. This type of structure has been termed paracrystalline. It is obvious that individual particles do not exist in carbon blacks, with the exception of thermal... 

In this connection, Fig. 2 provides a qualitative illustration for interpreting modulus change of an elastomer upon filler blending 9). A hydrodynamic or strain amplification effect, the existence of filler-elastomer bonds, and the structure of carbon black 10) all play a part in this modulus increase. 

Pinnick (57), from a study of crystallographic changes in carbon blacks between 1000° and 3000° C., suggests that for basal planes having diameters below 150 A. there is little tendency for the turbostratic structure to be lost. Above 150 A. interplanar forces, which increase as the square of the diameter, become great enough to cause orientation of the basal planes. Pinnick also finds that the diameter of the carbon black particle serves as an upper limit to the diameter of the crystallite which can be made from it. 

The carbon black in semiconductive shields is composed of complex aggregates (clusters) that are grape-like structures of very small primary particles in the 10 to 70 nanometer size range (see Carbon, carbon black). The optimum concentration of carbon black is a compromise between conductivity and processibility and can vary from about 30 to 60 parts per hundred of polymer (phr) depending on the black. If the black concentration is higher than 60 phr for most blacks, the compound is no longer easily extruded into a thin continuous layer on the cable and its physical properties are sacrificed. Ionic contaminants in carbon black may produce tree channels in the insulation close to the conductor shield. 

As in carbon-black-filled EPDM and NR rubbers, the physical network in silica-filled PDMS has a bimodal structure [61]. A loosely bound PDMS fraction has a high density of adsorption junctions and topological constraints. Extractable or free rubber does virtually not interact with the silica particles. It was found that the density of adsorption junctions and the strength of the adsorption interaction, which depends largely on the temperature and the type of silica surface, largely determine the modulus of elasticity and ultimate stress-strain properties of filled silicon rubbers [113]. 

Both of these effects refer to a high surface activity and specific surface of the filler particles [26, 27, 47]. In view of a deeper understanding of such structure-property relationships of filled rubbers it is useful to consider the morphological and energetic surface structure of carbon black particles as well as the primary and secondary aggregate structure in rubber more closely-... 

For a quantitative analysis of the structure of carbon blacks as shown in Fig. 17 it is useful to consider the solid volume Vp or the number of primary particles Np per aggregate in dependence of aggregate size d. In the case of fractal objects one expects the scaling behavior [1, 2]... 

Fig. 36 Schematic view of kinetically aggregated filler clusters in rubber below and above the gel point < the left side characterizes the local structure of carbon black clusters, build by primary particles and primary aggregates accordingly, every black disc on the right side represents a primary aggregate...

Structure of carbon black is directly related to the type of molecules in the feedstock employed,... 

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