Piezoresistivity of 3D-printed Thermoplastic Polyurethane/Carbon Black Nanocomposites

Abstract

Piezoresistive polymer nanocomposite materials represent a class of smart materials capable of converting mechanical deformation into measurable electrical signals. These materials, often composed of conductive fillers combined with a flexible matrix/substrate, are of significant interest for various applications such as structural health monitoring and wearable devices. The unique combination of mechanical flexibility and high piezoresistive sensitivity makes them superior to traditional sensing materials. Recently, different techniques have been developed to process these polymer nanocomposites for creating strain sensors. Among these, 3D printing has garnered considerable attention for its customizability and precision. However, a comprehensive understanding of the process-structure-property relationship is still lacking, hindering further optimisation of sensor performance. The effects of printing parameters, such as infill angle and layer orientation, on the piezoresistive response remain underexplored. This thesis systematically investigates the electromechanical behaviour of 3D-printed piezoresistive sensors, focusing on the investigation of the effects of infill angle and layer orientation on sensing performance. The study showed that as the infill angle increased, the mechanical properties of the sample decreased while the piezoresistive sensitivity (gauge factor, defined as ∆𝑅/𝜀𝑅0) increased. The sensitivity of the sample printed at an infill angle of 90° reached up to 17, with a fast response speed of 44 ms, and only 5% drift in the signal output under 1000 cycles of loading. Moreover, it was found that samples with a biaxial layout showed increased mechanical properties but with lower sensitivity. The work identifies the interplay between printing conditions and sensor functionality, providing insights into tailoring piezoresistive properties. This work also shows that the sensor can be used to detect the health of concrete.