Carbon black surface chemistry

The oldest method for the modification of carbon black surface chemistry is oxidation. Common oxidants include air, hydrogen peroxide, hypochlorites, nitric acid, nitrogen dioxide, ozone and persulfates. Each reagent produces a mixture of oxygen functional groups on the surface, with the distribution depending on the oxidant. Materials that disperse in water can be produced with sufficient oxidation, and hypochlorites and persulfates have been used to make water dispersible carbon blacks for inkjet inks. 

It is thus well established today that carbon black surface chemistry plays a very minor role, is any, in the reinforcement of general purpose elastomers. 

A new method for achieving stable attachment of organic functional groups to carbon black surface using diazonium chemistry, has been applied to the 4-aminophenyl disulhde (APDS) precursor. ... 

See also Carbon Black Colloid Chemistry Particle Sedimentation and Surface Chemistry. 

Compared to morphology, filler chemistry has been only slightly studied, partly because of the difficulty of such characterizations and more probably because since the 1970s reinforcement is broadly considered as a physical interaction between elastomer and filler. So carbon black chemical characterizations mainly date from the 1960s, and few new technical methods have been applied to carbon black surface characterization since then. The situation is somewhat different for silicas, because silica reinforcement is the consequence of a chemical reaction of silane with silica surface. Few studies have been published in the elastomer reinforcement area, probably because silica surface was already well characterized for other applications. 

Hayashi, S Handa, S. Tsubokawa, N. (1996). Introduction of Peroxide Groups onto Carbon Black Surface by Radical Trapping and Radical Graft Polymerization of Vinyl Monomers Initiated by the Surface Peroxide Groups. Journal of Polymer Science Part A Polymer Chemistry, 34,1589-1595... 

Tsubokawa, N. Funaki, A. Hada, Y. Sone, Y. (1982). Grafting onto Carbon Black Graft Polymerization of 5-Propiolactone onto Carbon Black Surface. Journal Polymer Science, Polymer Chemistry Edition, 20,3297-3304... 

Tsubokawa, N. Tsuchida, H. (1992b). Heat-resistant Polymer-grafted Carbon Black Grafting of Poly(organophosphazenes) onto Carbon Black Surface. Journal of Macromolecular Science, Pure Applied Chemistry, A29,311-321 Tsubokawa, N. Yanadori, K. (1992c). Reaction of Polymer Radicals formed by the Decomposition of Azopolymer with Carbon Black Surface. Kobunshi Ronbunshu, 49, 865-870... 

In the carbon black reinforcement of rubber, the chemistry of the carbon black surface is important. The amount and functionality of oxygen, nitrogen, and hydrogen on the surface varies with the method of preparation. Particle size itself is important, the generalization being that the finer the particle size the greater the reinforcement. Matters of ease of incorporation and fabrication as well as cost and other properties enter in to complicate the choice for any one application. 

The enormous importance of carbon in such diverse fields as inorganic and organic chemistry and biology is well known however, only the aspects of carbon relevant to catalysis will be described here. The main topics we are concerned with are porous activated carbons, carbon black as catalyst supports and forms of coking. Carbon is also currently used as storage for natural gas and to clean up radioactive contamination. Carbon is available at low cost and a vast literature exists on its uses. Coal-derived carbon is made from biomass, wood or fossil plants and its microstructure differs from carbon made from industrial coke. Activated carbons are synthesized by thermal activation or by chemical activation to provide desirable properties like high surface area. 

Adsorption Properties. Due to their large specific surface areas, carbon blacks have a remarkable adsorption capacity for water, solvents, binders, and polymers, depending on their surface chemistry. Adsorption capacity increases with a higher specific surface area and porosity. Chemical and physical adsorption not only determine wettability and dispersibility to a great extent, but are also most important factors in the use of carbon blacks as fillers in rubber as well as in their use as pigments. Carbon blacks with high specific surface areas can adsorb up to 20 wt% of water when exposed to humid air. In some cases, the adsorption of stabilizers or accelerators can pose a problem in polymer systems. 

The three parameters, mean primary particle size (or specific surface area), structure (or aggregate size), and surface chemistry (e.g. surface oxides), largely determine the application characteristics of carbon blacks. A summary of how these parameters affect color and performance appears in Table 31. 

A highly concentrated dispersion of carbon black is first prepared with a portion of the binder and solvent. The viscosity of this concentrate is a function of the particle size, structure, and surface chemistry of the black, the type of binder and its interaction with the pigment black, and the proportions of black, binder, and solvent. The final paint is made from the concentrate by adding more binder and solvent, its carbon black concentration is 3-8% referred to the solids content. Wetting agents are sometimes added to improve dispersibility and prevent flocculation. A number of concentrates for paint manufacture e.g., carbon black-nitrocellulose chips or carbon black -alkyd resin pastes, can be obtained from paint producers. 

Kinoshita did not discuss the possible reasons for these differences, nor has apparently anyone else, at least not convincingly. For example, based on everything known about carbon surface chemistry today, it is not easy to explain why electron transfer would occur on carbon blacks prior to 02 adsorption, and on graphite or GCs subsequent to 02 adsorption. 

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