Polypropylene-Carbon Nanofiber Composites as Strain-Gauge Sensor

Polymeric materials have been replacing other materials in various applications, from structural to electronic components. In particular, since the discovery of conducting polymers and the beginning of the manufacture of conducting composites with carbon fillers, their use in electronics has been growing. A group of electronic components with large potential for industrial applications such as structural monitoring, biomedical, or robotics are sensors based on the piezoresistive effect, fabricated from conductive polymers and/or composites. The aim of this article is to characterize the piezoresistive effect of conductive polymer composites based on polypropylene filled with carbon nanofibers, and to demonstrate a way of fabricating strain gauges from these materials, using industrial techniques. With this purpose, some films are prepared by shear extrusion, which allows the composites to be produced industrially in a standard nonexpensive process. Then, the dependence of the electrical response both on the preparation conditions and on the mechanical solicitations is measured. The obtained gauge factor values, up to 2.5, and piezoresistive coefficients up to 0.0019 mm(2)/N, prove the viability of these materials for fabricating strain-gauges, where their main advantages are the lower price and the ability to deal with much higher deformations, when compared to metal or semiconductor strain-gauges.