In this work, three different polyurethane (PU) foams were prepared by mixing commonly used isocyanate and polyol with different isocyanate indices (1.0:0.8, 1.0:1.0, 1.0:1.1). Then, the prepared polyurethane foam samples were coated by dip-coating with a fixed ratio of nitrogen-doped, bamboo-shaped carbon nanotubes (N-BCNTs) to obtain pressure sensor systems. The effect of the isocyanate index on the initial resistance, pressure sensitivity, gauge factor (GF), and repeatability of the N-BCNT/PU pressure sensor systems was studied. The pore volume was crucial in finetuning the PU-foam-based sensors ability to detect large strain. Furthermore, large pore volume provides suitable spatial pores for elastic deformation. Sensors with large pore volume can detect pressure of less than 3 kPa, which could be related to their sensitivity in the high range. Moreover, by increasing the pore volume, the electrical percolation threshold can be achieved with a minimal addition of nanofillers. On the other hand, PU with a smaller pore volume is more suitable to detect pressure above 3 kPa. The developed sensors have been successfully applied in many applications, such as motion monitoring and vibration detection.

In this study, a novel technology is reported to prepare a piezoresistive polyurethane-silicone rubber nanocomposite. Polyurethane (PU) foam was loaded with a nitrogen-doped bamboo-shaped carbon nanotube (N-BCNT) by using dip-coating, and then, impregnated with silicone rubber. PU was used as a supporting substrate for N-BCNT, while silicone rubber was applied to fill the pores of the foam to improve recoverability, compressive strength, and durability. The composite displays good electrical conductivity, short response time, and excellent repeatability. The resistance was reduced when the amount of N-BCNT (0.43 wt %) was increased due to the expanded conductive path for electron transport. The piezoresistive composite has been successfully tested in many applications, such as human monitoring and finger touch detection.

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