Effect of Melt Mixing Conditions on the Mechanical, Electrical, and Strain Sensing Properties of Carbon Nanotube–Styrene Butadiene Styrene/Thermoplastic Polyurethane Nanocomposites with a Double-Percolation Structure

Conductive polymer composites (CPCs) have been widely used in flexible strain sensors, while the preparation processes of flexible strain sensors are often complex and costly. Besides, obtaining high sensitivity and durability simultaneously remains challenging. Herein, a flexible strain sensor with a double-percolation structure composed of carbon nanotubes (CNT), styrene butadiene styrene (SBS), and thermoplastic polyurethane (TPU) was prepared by multistage melt mixing and hot pressing methods. The influences of processing conditions of the torque rheometer on the morphology, mechanical, electrical, and sensing properties of sensors were investigated. Relatively low mixing temperatures resulted in higher viscosity and shear force, as well as more uniform CNTs dispersion. Extended mixing time led to CNTs transfer from SBS to TPU, as well as miscibility of SBS and TPU, damaging the double-percolation structure. Therefore, optimizing the mixing temperature, speed, and time at 160 °C, 60 rpm, and 5-5-3 min (three stages) improved the sensing performance of CNT–SBS/TPU. Accordingly, the CNT–SBS/TPU sensor exhibited a high sensitivity of 9880.9, a low detection limit of 0.4