Comparing Carbon Black and Untreated Silica in Diene Elastomers

3 Comparing Carbon Black and (Untreated) Silica in Diene Elastomers 

Silicone rubber and, in general polar polymers, are by nature materials of choice for preparing silica filled systems however limited to niche applications, with respect to the range of properties that such specialty polymers may offer. In order to develop optimum reinforcing performance with more common diene elastomers, silica must be chemically treated as we will see below, because contrary to carbon blacks, silica particles do not develop spontaneous strong interactions with nonpolar polymers. It is nevertheless interesting to see that, even with comparable size and structure, pure silica does not affect the mechanical properties of vulcanized rubber compounds in the same manner as carbon black. 

This was clearly demonstrated in the excellent review paper by S. Wolffs who studied the effects of two comparable series of silica and carbon black in 50 phr filled natural rubber (RSSl) compounds, vulcanized with peroxide (Note that such a vulcanization system was chosen because there is no interference between silica and peroxide curing). Table 6.1 gives typical size and structure data for the two series of filler considered. It is worth imder-lining that there are no standard methods for characterizing silica. Either an existing method can be used as such because it does not depend on the filler 

Comparable Series of Precipitated Silica and Carbon Black 

However, in line with tensile modulus data, silica gives larger compression sets than carbon blacks. Despite the fact that the compounds investigated were (purposely) oversimplified with respect to industrial practices, the key information in the experiments reported by Wolff is that silica filled compounds exhibif definifely better dynamic properties that carbon black filled ones, namely higher rebounds and lower heat build-up. In addition the higher the specific area of fillers, the larger the differences between silica and carbon black loaded materials. Freund and Niedermeier made a similar 

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