The present work investigates the material properties of a thermosetting epoxy polymer modified with various reinforcements of micron-sized glass beads and rubber particles, and nano-sized silica particles and carbon nanotubes. The Young’s modulus of the modified epoxies with rigid additives was significantly increased, especially for the nanocomposites containing high contents of nanosilica or nanotubes.
The fracture testing showed that the combination of the soft rubber particles and carbon nanotubes provided the best way to improve the toughness and fatigue performance, because a synergistic effect on the fracture behaviour was obtained in the hybrid-modified epoxies. Fractography showed various mechanisms caused by the addition of the toughening particles, and the main toughening mechanisms are dependent on the modifiers used. Nanotubes operated the debonding, pull-out and void growth mechanisms improve the toughness and fatigue performance of their composites. The inclusion of the rigid spherical particles into the epoxy increased the toughness and fatigue performance via mechanisms of shear band yield and plastic void growth. Rubber cavitation was considered to be the main toughening mechanism in the rubber-modified materials.
Several dispersion methods were examined for the multi-walled carbon nanotubes, and the best way to get well-dispersed nanotubes without significant damage was identified. The level of the nanotube dispersion was assessed using a greyscale analysis and transmission optical microscopy. Finally, a sonication process using an ultrasonic probe was chosen to prepare the nanotube-modified epoxies.
Modelling work was carried out to predict the toughening contribution from the nanosilica and nanotubes. There was a good agreement between the predictions and the experimental results for the toughness. The modified Halpin-Tsai equation was used to calculate the increased modulus caused by the addition of the nanotubes, and the predicted modulus can fit well with the measured values, even at high nanotube contents which resulted in serious agglomeration
