Mechanical Behavior of 3D Printed Multiwalled Carbon Nanotube/Thermoplastic Polyurethane Nanocomposites

As the soft robotics industry continues to grow, the need for new materials and simplified manufacturing techniques are essential. Of interest is the development of highly flexible strain sensors that are easily integrated into these robotic components. Current strain sensing solutions using piezoresistive materials often involve complex fabrication techniques with multiple steps. Recent work by the authors has shown that thermoplastic polyurethane/multiwall carbon nanotubes (TPU/MWCNT) has good piezoresistive behavior and can be easily fabricated into strain sensors using Fused Deposition Modeling (FDM). This work expands upon that effort to characterize the mechanical properties of FDM-printed TPU/MWCNT as a function of the FDM processing parameters. In this study, the air gap, raster orientation, and MWCNT weight percent were varied and tensile tests performed. The stress-strain behavior, modulus of elasticity, and ultimate tensile strength (UTS) are compared to assess the influence of the processing conditions. Optical microscopy was also carried out to correlate the mechanical behavior to the printed mesostructures. The results show that with increased MWCNT content, the UTS decreased by as much at 47% for 2wt.%MWCNT, while the modulus of elasticity increased by 54%, compared to those of pure TPU. The results of this work provide an understanding of the mechanical performance in relation to the print parameters and sets the base to tune the mechanical properties of printed flexible functional nanocomposites.