Anisotropic properties of elastomeric nanocomposites based on natural rubber and sp2carbon allotropes

This work provides a comprehensive investigation of the anisotropic mechanical and electrical properties of elastomeric
nanocomposites based on natural rubber and sp2 carbon allotropes. They can be either nanometric and with high
shape anisotropy like Carbon Nanotubes (CNT) and lamellar nanographite, or nanostructured and nearly isometric like
carbon black. Studies were performed on calendered and compression molded plates. A complete mechanical characterization
along all main directions could be performed by a non-standard testing approach. Composites with nanometric, high aspect
ratio fillers gave rise to remarkable mechanical anisotropy, revealing an orthotropic and transversally isotropic response:
modulus values were very similar in the sheet plane and much larger (almost twice as much) in the orthogonal direction.
The electrical anisotropy achieved its maximum at lower CNT content. Composites with carbon black did not reveal mechanical
anisotropy, while, quite strikingly, a very large electrical anisotropy was observed for carbon black content close
to the percolation threshold. These results provide insights into the anisotropic behavior of nanofilled elastomers, and could
pave the way to their exploitation in advanced engineering design and biomimicking biomedical applications