Piezoresistive performance of polymer-based materials as a function of the matrix and nanofiller content to walking detection application

Abstract

Thermoplastics and thermoplastic elastomers can be combined with carbon nanotubes (CNT) for the development of piezoresistive composites with varying deformation ranges for sensing applications. This work reports on the influence of the polymer matrix on the mechanical and electromechanical properties of polymer composites prepared by solvent casting. CNT contents up to 5 wt% were dispersed in polymer matrices of different mechanical characteristics, including poly(vinylidene fluoride) (PVDF), styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) and thermoplastic polyurethane (TPU). In all cases, the chemical and thermal properties of the polymers were preserved after the addition of the nanofillers and good nanofiller dispersions were achieved for the polymeric matrices. The electrical properties of the composites are strongly related with the nature of the matrix. Thus, PVDF and SEBS show the lowest and largest percolation threshold, at 0.5 and 2 wt% CNT, respectively, and TPU showed an intermediate value of percolation threshold. The highest electrical conductivity was obtained at 5 wt% CNT composites (0.8 S/m) for the TPU. Piezoresistive sensibility in 4-point-bending and pressure modes shows the largest for the PVDF, for low deformation bending and pressure tests (GF ≈ 2.8 and PS ≈ 12 MPa−1, respectively). Thus, PVDF is the most suitable polymer matrix for low deformation applications, whereas TPU and SEBS are suited for large deformation application due to their stretchability. The different materials have been successfully implemented as pressure sensing materials for human walking detection, with a developed electronic circuit to measure, and compare, different polymer and composites materials. All composites can sense the human walk movement.