High-Linearity, Low-Hysteresis and Thermally-Stable MWCNT/Elastomer Characterization: Potential for Gait Parameter Estimation

This work proposes the integration of Multi-Walled Carbon Nanotubes (MWCNTs) into a urethane resin comprising polycarbonate (PC) and polytetramethylene ether glycol (PTMG) to develop sensors for smart clothing and textiles. Nowadays, flexible sensors are becoming interesting for both healthcare and sports because of ease of use and user comfort. Current solutions consisted of bulky and heavy devices that create discomfort for patients and athletes, such as Inertial Measurment Units (IMUs) and Global Positioning System (GPS) based systems. The MWCNT/Elastomer sensor characterization was evaluated both electrically and mechanically. Specifically, a tensile machine was used to stretch the sensor up to 25% strain at two strain rates, 5 mm/min and 30 mm/min. Cyclic tests and stress relaxation tests were used to assess sensor's resistance to strain, demonstrating good linearity (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$R^{2}&gt;0.89$</tex>), low hysteresis (5%), and high thermal stability (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3.6 \times 10^{-3} \% /^{\circ}C$</tex>). A Dynamic Mechanical Analysis (DMA) reveals the viscoelastic behavior of the sensor, including its rubbery plateau module of 2 MPa. The combination of these properties, including a negative temperature coefficient, makes the sensor particularly suitable for applications in sports environments, such as gait parameter estimation.