Carbon blacks structure

This term has its normal meaning as in the structure of vulcanised rubber but it now has a particular significance in relation to carbon black. See Carbon Black Structure. 

Important characteristics determining the quality of a feedstock are the C/H ratio as determined by elemental analysis and the BMC Index [4.7] (Bureau of Mines Correlation Index), which is calculated from the density and the mid-boiling point resp. the viscosity. Both values give some information on the aromaticity and therefore the expected yield. Further characteristics are viscosity, pourpoint, alkaline content (due to its influence on the carbon black structure), and sulfur content, which should be low because of environmental and corrosion considerations. 

As the carbon black structure may be reduced by the presence of alkali metal ions in the reaction zone [4.11], alkali metal salts, preferably aqueous solutions of potassium hydroxide or potassium chloride, are often added to the make oil in the oil injector. Alternatively, the additives may be sprayed separately into the combustion chamber. In special cases, other additives, e.g., alkaline-earth metal compounds which increase the specific surface area are introduced in a similar manner. 

An attempt was made recently to find characteristic values for the type and degree of aggregation using electron micrographs [4.28], However, neither visual comparisons with standard aggregates nor automatic picture analyses have led to a practical method for a quantitative characterization of the carbon black structure on a routine... 

DBP absorption mL/100 g ASTM D 2414 ISO 4656 DIN 53601 determination of the wetting point with dibutyl phthalate in a special kneeder as a measure of the carbon black structure... 

Another important property is the structure (see Section 4.1) which characterizes the coalescence of primary particles into aggregates resembling chains or bunches of grapes. The dibutyl phthalate (DBP) absorption is commonly accepted as a measure for the carbon black structure. Due to absorption phenomena the DBP number increases with increasing specific surface area. Oil absorption (or, in general, the vehicle demand) is as well an indicator for the structure, but it also depends on the wettability of the black surface. Since linseed oil is a polar system, oil absorption declines as the concentration of surface oxides rises. 

Packing of the primary carbon particle aggregates creates voids. The resulting void volume depends on the size and shape of the aggregates, the aggregate agglomeration, and the porosity of the primary particles. Therefore, the carbon black structure can be considered as the sum of a number of accessible voids by unit weight, namely... 

Even dynamic measurements have been made on mixtures of carbon black with decane and liquid paraffin [22], carbon black suspensions in ethylene vinylacetate copolymers [23], or on clay/water systems [24,25]. The corresponding results show that the storage modulus decreases with dynamic amplitude in a manner similar to that of conventional rubber (e.g., NR/carbon blacks). This demonstrates the existence and properties of physical carbon black structures in the absence of rubber. Further, these results indicate that structure effects of the filler determine the Payne-effect primarily. The elastomer seems to act merely as a dispersing medium that influences the magnitude of agglomeration and distribution of filler, but does not have visible influence on the overall characteristics of three-dimensional filler networks or filler clusters, respectively. The elastomer matrix allows the filler structure to reform after breakdown with increasing strain amplitude. 

The method is based on the premise that all interstices, known as void volumes, in the carbon black aggregates are filled with DBP. The surface of the carbon black is considered to be wetted and this new surface state is translated into a change in the torque required for the kneading machine. The DBP requirement thus allows conclusions on the degree of aggregation of individual carbon blacks. The rule the greater the DBP absorption, measured in ml g , the higher the carbon black structure. 

JB Donnet, TK Wang, E Custodero. STM and AFM Study of Carbon Black Structure. Proceeding of International Conference Eurolillers 95, Mulhouse (France), September 11-14, 1995, pp 187-190. 

Carbon black structure affects the physico-mechanical properties of the material, such as tensile strength, elongation, water absorption, tinting strength, die swell, etc., which are discussed under their respective topics in Chapter 5. 

Figure 18.16 shows that carbon black incorporation time, BIT, is affected by the addition of ZnO and by the properties of carbon black. If no ZnO is added, the incorporation time decreases as the carbon black structure increases. The opposite is true when ZnO is present during carbon black dispersion. The overall quality of the dispersion improves when ZnO is present and when mixing is carried out at elevated temperature Dispersion quality was assessed by optical measurements. 

The resolved spectra of these carbon blacks are shown in Figure 15. The bands at 1725,1595 and 1245 cm 1 observed in Monarch 1300 are also present in the different carbon blacks, but in varying proportions. Note that the bands at 1595 and 1245 cm 1 are even present in the completely unoxidized Sterling MT black. This reinforces the proposal that these bands are associated with the bulk carbon black structure and are only enhanced by the presence of surface species. As mentioned above, the sharp bands at 1135 and 1340 cm 1 appear in some of the carbon blacks but not in others as might be expected from sulfur impurities introduced from different feed stocks. 

Carbon black structure leads to values of C which are larger than those expected for spherical particles, evidently because swelling of polymer in the interstices of the primary aggregates is more severely restricted than at the free surface. 

The breakdown of secondary carbon black structure and its effects on viscoelastic behavior are also discussed in recent papers by Bartenev and associates (160, 161). 

Since primary carbon black structure tends to increase the effective volume loading, it will accentuate the hysteretic effects. However, because of the intimate relationships between primary structure, dispersibility and secondary aggregation, the influence of primary structure will not always emerge clearly. In carefully controlled experiments energy dissipation increases moderately with primary structure with little change in resilience. This is illustrated in Table 4 with data on some of the vulcanizates of Fig. 11, Section V-3. 

Table 4. Primary carbon black structure and hysteresis (60 phr of carbon black...

Eq. (32) contains no parameters characteristic of the filler. If it successfully represents data on one carbon black, then it should also do so for other blacks, irrespective of particle size or structure. The author s fragmentary data (212) on large particle furnace blacks indicates that this is true. The effects of carbon black structure at constant particle size are shown in Fig. 23 with data on the four carbons of Fig. 11. Although there is some scatter in the experimental points there is no systematic deviation by black structure. The line drawn through the data agrees nearly quantitatively with that of Harwood and Payne. 

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... 

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