Carbon black surface, bonded group

Before the 1970s, carbon black reinforcement of elastomers was generally considered chemical by nature (Wiegand, 1925). It was supposed that carbon black surface acidic groups were reacting with natural rubber basic moieties conducting to a strong covalent bond that was responsible for carbon black reinforcement ability. 

Figure 6.2 Bonded group of carbon black surface.

In the rubber industry the distribution of particle size is considered to be important as it affects the mechanical properties and performance. Aggregate size also varies with particle size. Aggregates can have any shape or morphology. The fundamental property of the filler used in a filled elastomer is the particle size. This affects the reinforcement of elastomer most strongly. One of the sources of reinforcement between the carbon black surface and the rubber matrix is the van der Waals force attraction. Also, rubber chains are grafted onto the carbon black surface by covalent bonds. The interaction is caused by a reaction between the functional group at the carbon black particle surface and free radicals on polymer chains. Hence, filler-rubber interface is made up of complex physical-chemical interaction. The adhesion at the rubber-filler interface also affects the reinforcement of rubber. When the polymer composites are filled with spherical filler (aspect ratio of the particle is equal to unity), the modulus of the composite depends on the modulus, density, size, shape, volume ratio, and number of the incorporated particles. 

ESCA has been used in the surface analysis of carbon black oxidized by various methods. Again, oxidation in air contributes to the most substantial loss of C-C bonds. Keto-enol groups were detected only in the samples which were oxidized in air. When other oxidative processes were employed, the groups detected were OH, C=0, and COOH. All other analytic methods provided similar information. 

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