Multi-wall carbon nanotubes do not necessarily improve the fracture behaviour of the epoxy matrix

Carbon nanotubes (CNTs) have been widely studied in the literature for their potential benefits as reinforcement in epoxy matrices. However, the enhancement that these nano-materials can provide to the corresponding epoxy matrix is largely dependent on the manufacturing process and other factors such as the wt.% or the nanotube type, showing different effects on the resulting mechanical properties. In this study, five contents of multi-wall carbon nanotubes (MWCNTs) were introduced in an epoxy resin to analyse their effects on both tensile and fracture properties, with the fracture behaviour being characterised in cracked and in notched conditions (with various radii). The experimental results showed a drastic deterioration of the tensile strength for MWCNTs contents higher than 0.1 wt.%, and no benefit was found in the fracture resistance (only conducted for 0.1 wt.% due to the negative effect observed in the tensile results). Therefore, it seems that the CNTs do not always improve the fracture behaviour of the epoxy matrix.