Agglomerates of carbon black

D-TEM gave 3D images of nano-filler dispersion in NR, which clearly indicated aggregates and agglomerates of carbon black leading to a kind of network structure in NR vulcanizates. That is, filled rubbers may have double networks, one of rubber by covalent bonding and the other of nanofiller by physical interaction. The revealed 3D network structure was in conformity with many physical properties, e.g., percolation behavior of electron conductivity. 

Incorporation - the carbon black is distributed into the rubber matrix but not into the desired state for complete reinforcement. At this stage of mixing the rubber penetrates the voids in the large agglomerates of carbon black. It is also at this stage that strong interaction between the rubber and black surface occurs in the case of small particle sized blacks with low structure, which makes the next step of dispersion difficult to achieve. 

Stokes, C.A., "Sonic Agglomeration of Carbon Black Aerosols , Chemical Engineering Process, Vol. 46, No. 8, 423-432, (1950). 

Schwarz, M.-K., Bauhofer, W., and Schulte, K. (2002) Alternating electric field induced agglomeration of carbon black filled resins. Polymer, 43, 3079-3082. 

The behavior of different grades in rubber is dominated mainly by surface area, structure (DBPA), and surface activity. All these parameters play a role in rubber reinforcement through different mechanisms, such as interfacial interaction between rubber and carbon black, occlusion of the polymer in the internal voids of the aggregate, and the agglomeration of carbon black aggregates in the polymer matrix. 

The polymer-carbon black filler reinforcement depends widely on the polymer type, carbon black type and structure. Another factor affecting this reinforcement is the filler-filler interaction which leads to the formatimi of three dimensional aggregation structures within the bulk of the rubber matrix. Figure 12 shows the aggregation and agglomeration of carbon black in the rubber. These aggregations takes various shapes which may be spherical or ellipsoidal with different major and minor... 

Illustration Kinetics of dispersion the two-zone model. The models for agglomerate rupture when integrated with a flow model are useful for the modeling of dispersion in practical mixers, as was discussed for the case of drop dispersion. Manas-Zloczower, Nir, and Tadmor (1982), in an early study, presented a model for the dispersion of carbon black in rubber in a Banbury mixer (Fig. 34). The model is based on several simplifying assumptions Fragmentation is assumed to occur by rupture alone, and each rupture produces two equal-sized fragments. Rupture is assumed to occur... 

Rumscheidt, F. D., and Mason, S. G., Particle motions in sheared suspensions. XII. Deformation and burst of fluid drops in shear and hyperbolic flow. J. ColloidScL 16,238-261 (1961). Rwei, S. P., Manas-Zloczower, I., and Feke, D. L., Observation of carbon black agglomerate dispersion in simple shear flows. Polym. Eng. ScL 30, 701-706 (1990). 

Fig. 17. Interactive forces in the dispersive mixing of carbon black. R, aggregate effective radius Rg, agglomerate effective radius F, interaggregate cohesive force [83]...

Studies on the kinetics of carbon black dispersion in various rubbers have been reported using a Brabender mixer fitted with cam-type rotors [110]. Dispersion rating, determined by visual inspection of photomicrographs, was found to depend strongly on mixing time. For an SBR emulsion, it was observed that there was an initial delay period where the carbon black agglomerates were thought to be fractured and incorporated into the rubber. Subsequently, the process of dispersion continued for a considerable time thereafter. 

Two-roll mills have been analyzed in terms of the pressure distribution and velocity profiles created between the rolls [95], the shear imposed on fluid elements exposed to these conditions in the nip region [129] and their resulting efficiency as dispersive mixing devices [130,131]. An earlier mathematical model was proposed to describe the dispersive mixing process of carbon black in rubber on roll mills, through consideration of agglomerate size distribution and... 

The most common example of dispersive mixing of particulate solid agglomerates is the dispersion and mixing of carbon black into a rubber compound. The dispersion of such a system is schematically represented in Fig. 3.22. However, the break up of particulate agglomerates is best explained using an ideal system of two small spherical particles that need to be separated and dispersed during a mixing process. 

The dispersion of carbon black into rubber is the classic example of dispersion of solid agglomerates. The mechanical and physical properties of the rubber (e.g., in tires) depend... 

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