The effect of the aspect ratio of carbon nanotubes on their effective reinforcement modulus in an epoxy matrix

The potentiality of carbon nanotubes as reinforcement material is not only due to their exceptional high modulus, but also to their high aspect ratio. Indeed, the nanotubes contribution to the mechanical reinforcement in a polymer is strongly dependent on their distribution within the hosting matrix. In fact, the clustering of carbon nanotubes does limit the theoretical enhancement of the composite mechanical properties by a reduction of their effective aspect ratio.In this work, the reinforcement efficiency of carbon nanotubes having different aspect ratios has been experimentally investigated at low filler contents in an epoxy system. From a theoretical point of view, the classical theory (Cox, 1952 [25]) concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube Random Contact Model (Philipse, 1996 [33]) which explicitly accounts for the progressive reduction of the tubes effective aspect ratio as the filler content increases. The validity of the proposed model was assessed by a comparison with available literature data, providing a good agreement.