Comparative study on TPU/multi-walled carbon nanotubes conductive nanocomposites for volatile organic compounds sensor applications

Novel thermoplastic polyurethane (TPU)/multi walled carbon nanotubes (MWCNTs) conductive nanocomposites were fabricated by direct solution compounding method for volatile organic compounds (VOCs) sensors applications. The results of field emission scanning electron microscopy (FESEM) and electrical conductivity test showed that MWCNTs formed ideal conductive networks in TPU matrix. The volume conductivity of TPU/MWCNTs nanocomposites increased from 10(-12) to 10(-4)S/mm, and the percolation value was 4.76 wt%. The size parameters of MWCNTs did not show obvious effects on the formation of conductive networks based on our comparative investigation. XRD and FTIR tests showed that MWCNTs enhanced the short range ordered structure in amorphous region of TPU due to the physical entanglement. The characteristic stretching of TPU showed no obvious change because of weak chemical interaction between MWCNTs and TPU. Moreover, MWCNTs effectively enhanced the thermal stability of the nanocomposites, as verified by TG analysis. The gas sensing property tests showed that the gas sensing response of TPU/MWCNTs nanocomposites mainly came from the resistance changes due to the disconnection of conductive networks, as a result of VOCs adsorption-swelling effects. The prepared nanocomposites showed superior selectivity, especially to benzene vapor when compared with formaldehyde and other gases. The parameters and contents of MWCNTs have a certain influence on the gas sensing response speed and recovery ability of the nanocomposites. In addition, the prepared TPU/MWCNTs nanocomposites displayed excellent repeatability and fast response to the change of electrical resistance (in seconds) after cyclic exposure to VOCs and pure dry air.