Carbon black filler-rubber interactions

H NMR transverse magnetisation relaxation experiments have been used to characterise the interactions between NR, isoprene rubber, BR, EPDM and polyethylacrylate rubbers with hydrophilic silica and silicas modified with coupling agents [124-129]. These studies showed that the physical interactions and the structures of the physical networks in rubbers filled with carbon black and rubbers filled with silicas are very similar. In both cases the principal mechanism behind the formation of the bound rubber is physical adsorption of rubber molecules onto the filler surface. 

Dutta, N. K., Choudhury, N. R., Haidar, B., Vidal, A., Dormet, J. B., Delmotte, L., and Chezeau, J. M. 1994. High resolution solid-state NMR investigation of the filler-rubber interaction 1. High speed iH magic-angle spinning NMR spectroscopy in carbon black filled styrene-butadiene... 

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... 

Medalia [16] demonstrated a further usefulness of this approach by using graphitised carbon blacks, which are known to have a weaker surface-affinity towards rubber. Thus, the method provides a means of examining the filler-rubber interaction. However, by the conditions set for deriving Equation 8.10, its applicability is limited to a small deformation. Also, only bi-particle interactions are considered in the equation and multi-particle interactions are assumed to be negligible. For the filled-rubber with the normal loading of 40-50 phr, the carbon black particles are crowded and the multi-particle interaction is important. 

However, the method requires elongational measurements of gum rubber and its unvulcanised compound. The experiments as well as the calculation are somewhat involved. If only a relative measure of the filler-rubber interaction is needed, dynamic mechanical measurements and subsequent comparison of modulus of the compound against that of the gum rubber are much simpler. Such comparisons with N550 carbon black were made with the samples listed in Table 9.2 and the moduli data of Figures 9.1 and 9.2 [12]. The modulus ratio is found to be independent of the frequency of the dynamic measurements but varies considerably among different gum rubbers. 

Journal of Applied Polymer Science 75, No.6, 7th Feb.2000, p.735-9 IMPROVEMENT OF FILLER-RUBBER INTERACTION BY THE COUPLING ACTION OF VEGETABLE OIL IN CARBON BLACK REINFORCED RUBBER Kundu P P... 

The important yet unexpected result is that in NR-s-SBR (solution) blends, carbon black preferably locates in the interphase, especially when the rubber-filler interaction is similar for both polymers. In this case, the carbon black volume fraction is 0.6 for the interphase, 0.24 for s-SBR phase, and only 0.09 in the NR phase. The higher amount in SBR phase could be due to the presence of aromatic structure both in the black and the rubber. Further, carbon black is less compatible with NR-cE-1,4 BR blend than NR-s-SBR blend because of the crystallization tendency of the former blend. There is a preferential partition of carbon black in favor of cis-1,4 BR, a significant lower partition coefficient compared to NR-s-SBR. Further, it was observed that the partition coefficient decreases with increased filler loading. In the EPDM-BR blend, the partition coefficient is as large as 3 in favor of BR. 

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. 

Another attempt by Tricas et al. to modify the surface of carbon black was by the plasma polymerization of acrylic acid [34]. Treatment with acrylic acid made carbon black hydrophilic. Plasma-coated carbon black was mixed with natural rubber and showed increased filler-filler interaction. The bound rubber content was reduced after the surface treatment of the filler. The authors also concluded that the surface of the carbon black was completely covered by the plasma polymer film, preventing the carbon black surface from playing any role in the polymer matrix. 

We restrict, in this paper, the discussions related to the reinforcement of elastomers to the investigation of a single filler, carbon black. We, moreover, mostly focus on the part played by surface chemical interactions in the properties of filler reinforced rubbers. 

---