Anisotropic compressive properties of multiwall carbon nanotube/polyurethane foams

• The anisotropy of MWCNT/polyurethane foam composites was investigated.
• Foam’s anisotropy increases with the addition of MWCNTs.
• Mechanical reinforcement was explained based on cell’s microstructure modification.
• The mechanical anisotropy can be represented by a tetrakaidecahedron cell model.

The anisotropic compressive properties of 0.1, 1 and 2 wt.% multiwall carbon nanotube/polyurethane foam (MWCNT/PUF) composites along the two main directions of transversely isotropic foams are investigated. Special attention is devoted to the anisotropic property-structure relationship of the nanocomposite foams governed by the cell size and morphology, which is investigated by microscopy and the use of existent micromechanical models which consider the cell geometry. Significant enhancement of compression properties with respect to the neat foam occurred for 0.1 and 1 wt.% tested along the foam’s free raising direction, while more modest property enhancement occurred along the foam’s transverse direction. The cells of the free rising foams are elongated and stronger in the rising direction and the foam’s structural anisotropy increases with the addition of small amounts (0.1 wt.%) of MWCNTs. The stiffness and strength ratios of the two main anisotropic directions may be reasonably predicted by using a simple parallelepiped cell model, but more accurate predictions are achieved when a tetrakaidecahedron representation is assumed, albeit more experimental parameters are necessary.