Conductive herringbone structure carbon nanotube/thermoplastic polyurethane porous foam tuned by epoxy for high performance flexible piezoresistive sensor

In this paper, we used epoxy (EP) as a third component to tune the electromechanical performances of the conductive porous foam. A directional ice-template freezing method was utilized to fabricate a carbon nanotubes (CNTs)/EP/thermoplastic polyurethane (TPU) porous foam with a herringbone-like structure. CNTs were homogeneously distributed in the skeleton of the foam. The microstructure of the herringbone-like foam was studied in detail from both the directions perpendicular and parallel to the freezing front movement direction. An ultralow percolation threshold (0.088 vol%) of the conductive foam was achieved. The strength of the CNTs/TPU/EP foam was significantly enhanced with the increase of the CNTs and EP contents. When the foams were exposed to a compression strain from 0 to 70%, the resistance of the porous material decreased in a good linear manner. The foams showed a good differenciation capability towards different compression strain amplitude. Upon multiple cyclic compressive process, the change of the resistance tended to be stable after several compression loading-unloading cycles' measurement. After a pre-compression treatment, the resistance response also became much stable on the basis of the re-arrangement of the conductive network and the stabilized cells structure of the foam. The porous foam possesses a rapid response speed (about 160 ms). Our flexible porous foam with a good chemical resistance can be used in ethanol to sense the finger pressing, and it showed excellent sensing performances when applied to monitor human body motions. (C) 2017 Elsevier Ltd. All rights reserved.