A comparison between strain sensing behaviors of carbon black/polypropylene and carbon nanotubes/polypropylene electrically conductive composites

Resistivity variations of carbon black (CB)/polypropylene (PP) and carbon nanotubes (CNTs)/PP conductive composites subjected to tensile strain, that is, the strain sensing behaviors, were studied detailedly. With increasing strain to the maximum value, 3%, the responsivity (ΔR/R0, R0 is the original resistance, ΔR is instantaneous change in resistance) increased in exponential and linear fashion for CB/PP and CNTs/PP, respectively, the phenomenon was explained by the tunneling theory. More interestingly, when 10 extension-retraction cycles were applied, for CB/PP, values of max and min ΔR/R0 increased gradually with increasing the cycle number; while for CNTs/PP, max and min ΔR/R0 values became more and more negative. It is suggested that the difference mainly depends on the distinction in the microstructure of conductive fillers, the interaction between fillers and matrix and the hysteresis effect resulting from viscoelastic behavior of composites. A schematic illustration was proposed to illustrate the mechanism of the different sensing behaviors.