I. INTRODUCTION

The reinforcement of elastomers by particulate fillers has been extensively studied in the past, particularly in the 1960s and 1970s. The first reason is naturally the drastic changes in mechanical properties that induces fillers reinforcement: many of the usual applications of elastomers could not be envisaged without the use of particulate fillers. The other reason seems to us to be of a very different nature, and probably resides in the mystery of the reinforcement mechanism that has fascinated many scientists and remains, despite their efforts, mainly not understood today.

It is necessary to define precisely what is reinforcement, because this word covers very different meanings when applied to thermoplastics, thermosets, or elastomers. Confusion is mainly due to the fact that reinforcement qualifies an increase in mechanical properties, but what is expected as mechanical properties is very different considering the different matrices and applications.

For plastics, reinforcement results in an increase in modulus and hardness. The effect of particulate fillers is quite clear, they replace a part of the matrix: so modulus becomes higher, but deformation at break decreases in the same time.

The situation is very different for elastomers: the use of reinforcing fillers induces a simultaneous increase modulus and deformation at break. Curiously, the replacement of a part of the deformable matrix by solid objects doesn t reduce its deformability. The increase of these two antagonistic properties characterizes elastomer reinforcement.