Sensing of large strain using multiwall carbon nanotube/segmented polyurethane composites

Multiwall carbon nanotube (MWCNT)/elastomeric composite films were fabricated using two segmented polyurethanes: an in-house synthesized one (SPU) and a commercial medical grade one (Tecoflex (R), TF). Electrical, mechanical, and electromechanical (piezoresistive) properties of both composites were evaluated as a function of the MWCNT weight concentration (1-10 wt %). An increase in electrical conductivity for both types of polymers was observed for MWCNT concentrations as low as 1 wt %. The electrical conductivity of MWCNT/TF composites was higher than that achieved for MWCNT/SPU composites. Mechanical properties of 8 wt % MWCNT/SPU composites showed a threefold increase in stiffness compared to neat SPU. The changes in electrical resistance of the composites showed higher sensitivity to strain for lower MWCNT concentrations. The piezoresistive signal of the composites allows to measure strains up to approximate to 400% before electrical depercolation occurs. The strain at which electrical depercolation occurs depends on the conductivity of the composite in its unloaded state. This kind of composites may find sensing applications in prosthetics, biomedical devices, and smart textiles. (c) 2013 Wiley Periodicals, Inc.