Nanofillers may improve the fracture toughness of polymer-based nanocomposites. The occurrence of agglomeration has been reported as one of the most important challenges to limit the potential of nanofillers for improving the fracture toughness of nanocomposites. Hybridization has been mentioned as one of the simple solutions to overcome the agglomeration phenomenon. In this regard, in the current paper, the effect of addition of multiwalled carbon nanotubes (MWCNTs) and MXenes on the fracture toughness of epoxy nanocomposites were investigated. Hence, 0.1, 0.3, or 0.5 wt% of MWCNTs and Ti3C2Tx MXenes nanofillers separately or in hybrid were added to an epoxy system using ultrasonication technique. The compact tension shear sample was employed to determine the mixed mode I/II fracture toughness of nanocomposites. The results manifested that by incorporation of the hybrid nanofillers into the epoxy nanocomposites, the mode I, mixed mode I/II, and mode II fracture toughness were improved by 53, 88, and 146% compared to the pure epoxy polymer, respectively. Moreover, it can be stated that the nanocompsoites toughened by hybrid nanofillers have better performance under different loading conditions compared to the nanocompsoites reinforced by single nanofillers, i.e., MXenes or MWCNTs. The fracture toughness improvement caused by hybridization and subsequently the occurrence of toughening mechanisms related to the well-dispersed nanofillers was explained by micrographs taken from the fracture surface of the specimens.
