Rubber reinforcement

The incorporation of nanometric fillers in an elastomer matrix enables a significant improvement in final properties such as stiffness, modulus, fracture energy, resistance to tearing and cracking, and resistance to fatigue and abrasion. This mechanical reinforcement is of particular commercial interest in the tire sector, where it improves tread wear, sidewall strength, etc.

Another consequence of incorporating fillers into an elastomer is a significant change in the rubber's dynamic properties, known as the "Payne effect". This phenomenon, of great importance to the rubber industry, has attracted a great deal of interest. The network of charges formed, via direct charge/charge interactions or via a pattern of elastomer layers immobilized on the surface of the charges, appears to be the main origin of the mechanisms governing the dynamic response.

Moreover, when subjected to large deformations or high stresses, filled (and vulcanized) elastomers exhibit an atypical hysteresis known as the "Mullins" effect. This behavior is not yet fully understood, but a consensus exists on the microscopic damage mechanisms behind the effect: limited extensibility of chains subjected to stress amplification, breakage or slippage...

These singular properties or behaviors depend on a large number of parameters such as filler volume fraction, shape and size, as well as interactions between fillers and/or between fillers and matrix, leading to elastomer adsorption on the filler surface, which has been shown to play a key role in the reinforcement mechanism. Furthermore, the quality of filler dispersion and distribution is very important. Generally speaking, the better the dispersion and distribution of fillers in the matrix, the better the properties. In the tire industry, for example, good filler dispersion generally reduces viscoelastic energy loss and, consequently, rolling resistance.

A wide variety of fillers are used in rubber compounds, but it is mainly carbon blacks and silicas that are found in the majority of industrial formulations. However, it should be noted that there are other types of fillers (reinforcing or weakly reinforcing) which have little or no influence on the mechanical properties of compounds. Their use is economically motivated (Kaolin, talcs, calcium carbonates...). Silicas are generally sought after for their significant reduction in rolling resistance, and hence fuel consumption. They are now widely used in passenger car tire tread formulations. Carbon blacks, on the other hand, are widely used in heavy-duty applications (or even in passenger car tires, in addition to silica) for their contribution to tire wear and durability.