Tensile piezoresistivity and disruption of percolation in singlewall and multiwall carbon nanotube/polyurethane composites

Carbon nanotube elastomeric composite films were fabricated by solution casting using singlewall and multiwall carbon nanotubes (SWCNTs and MWCNTs) and two thermoplastic-elastomers polymer matrices, an in-house synthesized segmented polyurethane and a commercial one. The CNTs are first characterized and the electrical conductivity, mechanical properties and piezoresistive response of the SWCNT and MWCNT composites with 8 wt% are evaluated. For both polymer matrices, the electrical conductivity of composites made from MWCNTs is higher than that achieved for composites made from SWCNTs. Evaluation of the strain–electrical resistance relationship of the composites shows a dependency of the piezoresistive sensitivity on the kind of CNT (SWCNT or MWCNT) and matrix electrical and mechanical properties. Above a specific strain threshold, electrical percolation is disrupted under tensile loading. The strain level at which this happens is larger for composites made with MWCNTs than for composites made with SWCNTs.