Effect of sub-micron silica fillers on the mechanical performances of epoxy-based composites

Solid state thermo-mechanical properties, as well as low and large strain mechanical behaviour, of epoxy composites filled with sub-micron pyrogenic silica are discussed in this paper. The reinforcement mechanisms involved are investigated. Two distinct series of pyrogenic silica were used: hydrophilic silica with various specific surface areas and silica grafted with various organo-modifications. Furthermore, two series of networks, having either a high or low crosslink density, and resulting thus either in glassy or rubbery materials at room temperature, were considered. Dynamic mechanical analysis, uniaxial tensile tests and fracture mechanic tests were performed. All our results showed that pyrogenic silica leads to an improvement of network mechanical properties both in the glassy and rubbery states. The simultaneous increase of stiffness and toughness was observed, demonstrating the great potential of pyrogenic silica for the reinforcement of thermosetting systems. This exceptional behaviour has been interpreted in terms of the interactions and morphology developed. (c) 2007 Elsevier Ltd. All rights reserved.