Mechanical characterization and fractographic study of epoxy–kaolin polymer nanocomposites

In this work the mechanical behavior of composite materials formed by a diepoxy–diamine (epoxy) thermosetting matrix filled with kaolin intercalated with ethylenediamine (K–EDA) was studied. Fracture toughness experiments showed that an addition of 2wt% K–EDA to the epoxy matrix causes an approximately 24% increase in the critical stress intensity factor (KIC). The study of fracture mechanisms was completed using the double-notch four-point-bending test. The presence of kaolin particles in the matrix induces crack branching and deflection mechanisms. Furthermore, observation of the fracture surface revealed the presence of tails near kaolin particles, which is consistent with crack-pinning. The present study indicates that kaolin clay can be effective in toughening epoxy at small quantities if it is reasonably well dispersed.