Silane coupling, precipitated silica

Various additives and fillers may be employed. Calcium carbonate, talc, carbon black, titanium dioxide, and wollastonite are commonly used as fillers. Plasticizers are often utilized also. Plasticizers may reduce viscosity and may help adhesion to certain substrates. Thixotropes such as fumed silica, structured clays, precipitated silica, PVC powder, etc. can be added. Adhesion promoters, such as silane coupling agents, may also be used in the formulation [69]. 

Scheme 3.4 Probable mechanism of bonding between ENR and precipitated silica in the presence of silane coupling agent...

Two major breakthroughs have transformed this facility product into a reinforcing filler that can achieve all carbon black mixes properties with, in addition, a decreased hysteresis of major interest for tire applications. The first step was made in the 1970s by Wolff, who proposed a specific silane coupling agent, the TESPT [11]. The second step arises in the 1990s with an R. Rauline s patent, which introduces the use of specific precipitation silica, elastomers, and mixing conditions to achieve reinforcement [12],... 

The reaction of a bifunctional organosilane with precipitated silica involves the hydrophobation of the alkoxy group of the silane with a surface silanol group of the silica, followed by reaction of the sulfur-containing function of the silane with an olefin group of the elastomer to afford a covalently bonded structure. This silane-coupled silica is useful in improving the abrasion resistance of silicas to levels of carbon blacks, and promoted their use in the treads of radial passenger tires. 

Silane coupling agents are widely used to improve the performance of mineral fillers in elastomer systems. The silanes most commonly used are the various sulfur-based ones and the vinyl and amino functional. The sulfides are generally used both pre-coated and in situ . The fillers most often used in conjunction with silane coupling agents are precipitated silicas and clays. The primary objective of the treatment is to improve polymer to filler bonding, although other benefits such as lower viscosity, better dispersion and reduced water adsorption are also observed. 

N. Hewitt, Proceedings of Silane Coupling of Precipitated Silica Functional Tire Fillers 2001, Intertech, Fort Lauderdale, FL, USA, 2001, Paper No.6. 

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