Electro-mechanical properties of thermoplastic polyurethane films and tubes modified by hybrid carbon nanostructures for pressure sensing

Electrical and piezoresistive properties of hybrid nanocomposite films and tubes made of a segmented aliphatic polyurethane modified with multilayer graphene sheets (MLGSs), multiwall carbon nanotubes (MWCNTs), and hybrid mixtures of both, were investigated. Hybrid nanocomposites were fabricated at a total weight concentration ( Φ T ) of 5 wt.%, with relative weight concentration of MLGSs with respect to MWCNTs ( Φ R ) of 25%, 50% and 75%. The electrical conductivity of these films is dominated by the MWCNT network, observing electrical MLGS-MWCNT collaborative effects only for Φ R = 25%. Dielectric impedance spectroscopy indicates that the nanocomposites display capacitive effects at frequencies higher than tens of Hz, which is explained by interfacial polarization. The burst pressure and circumferential stiffness of internally pressurized tubes fabricated from these films is slightly higher for tubes containing only MWCNTs. The strain fields in the pressurized tubes, determined by digital image correlation, showed localized strain gradients, and the piezoresistive response of the electro-conductive tubes was nonlinear. The highest pressure sensitivity factor (4.59 kPa−1) was obtained for hybrid nanocomposite tubes with Φ R = 25%.