Reinforcement efficiency of multi-walled carbon nanotube/epoxy nano composites

Mechanical reinforcement of polymer matrices loaded by carbon nanotubes is expected to benefit by both the high aspect ratio and the very high modulus of such nanofillers and, consequently, it depends not only by their content within the hosting system but also by the state of dispersion. This work analyses the effect on the bending modulus of dispersed multi-walled carbon nanotube (MWCNT) into an epoxy system. Results indicate that reinforcement efficiency is characterised by two limiting behaviours whose transition region coincides with the development of a percolative network of nanotubes. Well below the percolation threshold, the carbon nanotubes, contribute to the composite modulus with their exceptional modulus (in this case a value of 1.780 TPa was found), whereas it dramatically decreases above this limit due to the reduction of the effective aspect ratio and the micron sized cluster formation. An estimate of the maximum reinforcement induced by carbon nanotubes has been proposed based on percolation and stress transfer theory for large aspect ratio fillers.