Preparation and Performance of Biaxially Stretched CNT–SBS/EVA Flexible Strain Sensor With Double Percolation Structure

Developing flexible and wearable strain sensors that combine high performance and cost-effectiveness remains a challenge. In this work, a carbon nanotube/styrene–butadiene–styrene/ethylene vinyl acetate copolymer (CNT–SBS/EVA) flexible strain sensor with a double percolation structure was prepared by melt mixing and biaxial stretching at different stretching ratios (SRs). As the SR increased, the dispersion and orientation of the CNTs were further improved. Compared with the unstretched 2 wt.% CNT–SBS/EVA-1.0 sample (strain range 100%, gauge factor (GF) = 1237.95), the mechanical properties, sensitivity, and strain detection range were significantly improved after biaxial stretching. The elongation at break of the 2 wt.% CNT–SBS/EVA-1.5 (biaxially stretched at a SR of 1.5) sample increased by 310%. It exhibited higher sensitivity (GF = 176480.58), good linearity ( R 2 = 0.95) and a wider strain detection range (200%), as well as superior sensing performance and durability (2000 cycles), achieving improved performances. Finally, the practical value and potential applications of the CNT–SBS/EVA sensor in the monitoring of human physiological signals were demonstrated through response tests of different strain levels, such as joint and muscle movements.