White filler reinforcing agents

An activator in rubber compounds containing organic accelerators. In polychloroprene, zinc oxide is considered to be the accelerator rather than the activator. The use of zinc oxide as a reinforcing agent and as a white colouring agent is obsolescent. Zinc oxide is manufactured by either the French (or indirect) process or by the American (or direct) process. It can be used as a filler to impart high thermal conductivity. 

Vulcanized rubber compounds are usually reinforced by inorganic filler and/or carbon black to improve the mechanical properties, the thermal stability and the gas barrier properties of the bulky polymer. Carbon black is the most suitable reinforcing agent in the rubber industry thanks to the strong interaction with the polymer matrix. However, due to its polluting nature, the ubiquitous black color of the compounded material and its dependence on petroleum stock pushed the academic and industrially research to look out for other so-called white filler. In this sense, clays seem to be a good choice to replace conventional filler increasing the bulky PB performances. 

Most rubber products are black because of the supremacy of carbon black as a reinforcing agent, so colour does not play an important role in most industrial applications. For those applications where colour is important, the selection of filler is restricted to those non-black fillers, which are able to provide the properties required. The effect of these materials on colour is readily predictable from the whiteness of the filler. It is important, however, not to rely too heavily on the optical qualities of fillers as they are not produced for primary pigmentation purposes. 

Substitution of carbon black filler (or a significant part of it) with white reinforcing fillers (e.g. silica), as carbon black has also been found to act as a nitrosating agent. 

Rubber threads are susceptible to oxidative degradation, and high concentrations of antioxidants are added to the mixture to make the high surface area fibers more resistant. Pigments, such as titanium dioxide, are used as fillers or to impart whiteness to the thread. Carbon black reinforcement is used in colored rubber materials. Other agents include accelerators and activators to promote the vulcanization process. With all the additives, a typical high grade rubber thread contains less than 85% elastomer. 

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