Carbon black localization, rubber

This behavior can be understood if a superimposed kinetic aggregation process of primary carbon black aggregates in the rubber matrix is considered that alters the local structure of the percolation network. A corresponding model for the percolation behavior of carbon black filled rubbers that includes kinetic aggregation effects is developed in [22], where the filler concentrations and c are replaced by effective concentrations. In a simplified approach, not considering dispersion effects, the effective filler concentration is given by ... 

Proton spin resonance measurements on carbon black filled rubbers confirm the relatively small effect of the black on local segmental mobility. Waldrop and Kraus (107) were unable to find evidence for two spin-lattice relaxation times (one for surface rubber and one for bulk rubber) and found very little effect of carbon blacks on the position of the minimum in the spin-lattice relaxation time (7j) vs. temperature curve. The shape of the curve was also substantially unaffected (107). Extraction of free rubber from an uncross-linked SBR-HAF black mix did not accentuate the effect of the carbon black. More recently Kaufmann, Slichter and Davis (108) reported the observation of two spin-spin relaxation times (T2) in the bound rubber phases of polybutadiene and ethylene-propylene rubber, each reinforced with 50 phr of an SAF black (155 m2/g surface area). The amount of fully immobilized polymer was only 4% of the total, but the remainder of the bound rubber displayed... 

FIGURE 21.18 Force-deformation curves of local points indicated by open circles in Figure 21.15c. The curve fitting against Hertz model are superimposed on each curve, (a) Carbon black (CB) region (upper circle), 1.01 0.03 GPa, (b) interfacial region (middle circle), 57.3 0.8 MPa, and (c) rubber region (lower circle), 7.4 0.1 MPa. 

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...

The various assessments of the effects of carbon black on local segmental mobility by thermal and NMR measurements appear consistent with our understanding of carbon black-rubber bonding. As mentioned above, it has been estimated (91) that in a typical reinforcing furnace black only about 5 % of the surface is involved in chemisorptive attachments. Assuming 40 A2 for the area occupied by a monomer unit, one calculates 0.17 x 10 4 moles of chemisorptive attachments per gram of rubber for a loading of 100 phr of HAF black (80 m2/g). This is about... 

In view of the long history of research efforts on filled rubbers, it is not surprising that the initial works on filled polymer blends appeared in publications authored by rubber compounders and carbon black vendors [17, 18]. For instance, Walters and Keyte [17] observed that the compound ingredients, such as CB and zinc oxide, were not homogenously dispersed in rubber blends. Hess et al. [18] also reported a series of fundamental observations. First, they observed that filler particles tend to remain in the lower viscosity phase, in the absence of significant filler-matrix interactions. However, in the presence of strong polar-polar interactions between the filler particles and one of the phases, the particles were found to be selectively dispersed in the more polar phase and the viscosity became less important. More recently. Portal et al. [19] also presented similar observations about selective localization of CB particles in the natural rubber (NR) phase in NR/ polybutadiene blends. 

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