High-strength, flexible and cycling-stable piezo-resistive polymeric foams derived from thermoplastic polyurethane and multi-wall carbon nanotubes

In this work, high strength, flexible and cycling-stable piezoresistive thermoplastic polyurethane (TPU)/multi-wall carbon nanotubes (MWCNTs) composite foams were fabricated by a solution-blending method and supercritical carbon dioxide (ScCO2) foaming process. The micriocellular structure (1-10 mu m) of the TPU/MWCNTs composites enhanced the energy storage and reduced the conductive percolation threshold. The compressive strength and compressive modulus of the composites were 1.05 MPa and 3.79 MPa. Percolation threshold of the foamed composites decreased from 0.90 vol% to 0.31 vol%. The prepared TPUC5.0 foam (the content of MWCNTs is 5%) had high sensitivity, wide strain range, and stable resistance. The piezoresistive current was relatively stable, and showed high repetitive force-electric conversion behavior in 1000 cycles. Thus, polymeric foams are suitable for real-time monitoring of human foot movement using wearable strain sensors.