Investigation of micromechanical properties and strain sensing behavior of electrically conducting and Piezoresistive flexible copolyester/Carbon Nanotubes Nanocomposites
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Institute of Science and Technology, Chemistry
Abstract
Various concentration of multiwalled carbon nanotubes (MWCNT) as conductive filler was
incorporated into poly(butylene adipate-co-terephthalate) (PBAT), a flexible biodegradable
copolyester by melt-mixing followed by compression moulding. Deformation behavior of
electrically conductive nanocomposites was correlated with piezoresistivity, leading to their
strain sensing behavior. Structural and morphological characterization of the materials were
determined by Fourier transform infrared (FTIR) spectroscopy and microscopic techniques
while thermal stability and crystallization behavior were analyzed by thermogravimetric analysis
(TGA) and differential scanning calorimetry (DSC), respectively. Comparative analysis of FTIR
spectra of PBAT and PBAT/MWCNT nanocomposites suggested a physical matrix-filler
binding force to form the composite microstructures. Microscopic techniques revealed an
entangled CNT-network uniformly spread in the polymer matrix. Increased thermal stability of
the materials was suggested by TGA, attributed to a good filler-matrix interfacial interaction.
DSC results revealed the retarded crystallization process of the polymer with the formation of
less perfect crystals. Increasing tensile modulus, Martens Hardness (HM) and indentation
modulus (EIT
), and decreasing maximum indentation depth (hmax
) (by 50%, 50%, 100% and 32%
on incorporation of 5 wt-% of fillers, respectively) confirmed the mechanical reinforcement of
composites by MWCNT. Volume resistivity observed in the nanocomposites suggested the
suitability of nanocomposites for strain sensing applications. An exponential-like increment of
relative resistance change (ΔR/R0
) of the nanocomposites as a function of strain confirmed their
piezoresistivity. Applicability of nanocomposites as low-strain sensing materials was suggested
by their reproducible ΔR/R0
values from 2% to 8% strain during cyclic strain test. Electron beam
(EB) irradiation induced crosslinking of the nanocomposites was employed as a strategy to
improve the strain sensing behavior of the nanocomposites. Cyclic strain test of irradiated
samples (dose: 150 and 200 kGy) exhibited the improvement (up to 10% strain), attributed to
their enhanced elastic deformability. The nanocomposites irradiated with the highest dose (300
kGy) exhibited no correlation between ΔR/R0
and strain, attributed to the formation of a 3D
network of polymer crosslinks restricting the homogeneous deformation of the CNT-network.
Moderate degree of EB irradiation induced crosslinking of polymer nanocomposites can be a
strategy to improve their strain sensing behavior.
Keywords: nanocomposites, biodegradability, electrical conductivity, piezoresistivity, strain
sensing, electron beam irradiation, crosslinking