Electrostrictive thermoplastic polyurethane-based nanocomposites filled with carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH): Properties and improvement of electromechanical activity

Abstract The impact of small amounts of carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) added into a polyether-based thermoplastic polyurethane elastomer (TPU) was studied considering mainly on the morphological, mechanical, electrical and electrostrictive properties. The electrostrictive properties were measured by the analysis of the deformation response occurring under external electric fields E applied on 50 μm-thick films. Dielectric measurements were carried out in order to determine the percolation threshold fc, which was found near 1 v% loading. This volume fraction leads to a very high dielectric permittivity e r ′ up to ≈330, i.e. about 50 times higher than that of the pure TPU, where e r ′ ≈ 6 – 7 . The thickness strain SZ and apparent electrostrictive coefficient M were measured at low electric fields, E ⩽ 4 V/μm, by low frequency of 0.1 Hz. The maximum induced-compressive strain was obtained from an optimal volume fraction of 0.8 v% which yielded to a high Sz = 11.5%, corresponding to almost a threefold increase of M compared to the neat TPU. Beyond fc, the conductivity sharply raised up and thus the electrostrictive activity disappeared.