Electrical properties and piezoresistive evaluation of polyurethane-based composites with carbon nano-materials

The present study assesses the applicability of carbon materials-embedded polyurethane (PU) composites characterized by high piezoresistive capability, as a traffic loading sensor. PU composites incorporating multi-wall carbon nanotubes (MWNTs), expanded graphite (EG), and a hybrid of MWNTs and graphite nanoplatelets (GNPs) were fabricated and their electrical conductivities were measured in an effort to determine the most suitable filler type for the piezoresistive sensor and its optimum content ratio. The best electrical characteristics were achieved by the MWNT/PU composites as exhibiting the percolation threshold at 5 wt.% of MWNT and the maximum electrical conductivity of 0.33 S/m at 7 wt.%. Accordingly, the MWNT/PU composites were prepared as a piezoresistive sensor, and its sensing capabilities and durability were examined by three different tests, i.e., lab-scale loading, vehicular loading, and cyclic wheel loading tests. The composite with MWNT 5 wt.% showed the best sensing capability in terms of the electrical resistance change rate obtained from the lab-scale and vehicular loading tests. In addition, the cyclic wheel loading test demonstrated that the 5 wt.% MWNT-embedded PU composite was durable during 2000 cycles of the wheel loading.