Piezoresistivity and strain-sensing behaviour of poly(butylene adipate-co-terephthalate)/multiwalled carbon nanotube nanocomposites

Abstract

Multiwalled carbon nanotubes (MWCNTs) at different concentrations, ranging from 0.5 to 10 wt%, as a conductive filler, were incorporated into poly(butylene adipate-co-terephthalate) (PBAT), a flexible biodegradable copolyester, via melt-mixing, followed by compression moulding. The electrical conductivity of the prepared nanocomposites was evaluated by considering their volume resistivity value. The volume resistivity values of the nanocomposites suggested a quite low percolation threshold between the MWCNT concentration of 0.5 and 1 wt%. The corresponding volume resistivity values of the nanocomposites in the range of (6.90 ± 3.16) × 10⁵ Ω cm to (1.24 ± 0.41) × 10¹ Ω cm implied their suitability for strain-sensing applications. The change in the electrical resistance of the nanocomposites was measured simultaneously with tensile testing to evaluate their piezoresistivity. The deformation behaviour of the nanocomposites was correlated with relative resistance change (ΔR/R₀) via a cyclic-strain test to investigate the stability of their strain-sensing behaviour. A non-linear and exponential-like increment in the ΔR/R₀ values of the nanocomposites as a function of mechanical strain during tensile stretching confirmed their piezoresistivity. ΔR/R₀ values fitted well with an increase in applied mechanical strain from 2% to 8% during the cyclic-strain test, which revealed the low-strain sensing potential of the nanocomposites, provided by their stable and intact microstructure formed via continuous stretching and releasing during the test; this was further supported by the reproducibility of the ΔR/R₀ values in the cyclic-strain test with 7% applied strain in 15 cycles. Additionally, the uniformly extended net-like morphology of the nanocomposites with an entangled network of MWCNTs throughout the polymer matrix was revealed by their electron micrographs.