Synergistic enhancement of fracture toughness in multiphase epoxy matrices modified by thermoplastic and carbon nanotubes

Herein, we report the development of multiphase epoxy-based nanocomposite blends with enhanced fracture toughness and controlled microstructure. The blends are based on bifunctional and tetrafunctional epoxy resins, suitable for a wide range of applications particularly as matrices for advanced high temperature fibre reinforced composites with glass transition temperatures exceeding 200° Celsius. The multiphase blends comprise nanoscale (carbon nanotubes) and microscale (phase separating thermoplastic) inclusions which together form unique multiscale morphologies capable of dissipating crack energy through different energy absorption mechanisms. This work provides, for the first time, an in-depth investigation of the interactions between the nano- and micro-scale toughness modifiers which under appropriate conditions lead to a synergistic enhancement in the fracture toughness of the resin. A secondary agglomeration of carbon nanotubes during curing was shown to be suppressed by the phase separating thermoplastic particles, leading to a well dispersed state, justifying the synergistic increase in fracture toughness of the resulting blends. The molecular architecture of the epoxy matrix, in particular, the number of epoxide functional groups, was shown to be of significant importance in determining the final microstructure of the modified blends following curing reaction.