Design and Strain Sensing Performance of Spiral-Wrapped Composite Conductive Yarn Based on Graphene/Carbon Nanotubes

This article first combines graphene (Gr) with multiwalled carbon nanotubes (MWCNTs) to obtain a low-viscosity conductive ink with a synergistic effect to improve the flexible sensor’s electrical performance. It then uses a simple, low-cost impregnation-drying method to prepare conductive cotton yarn (CCY). CCY wraps on a highly elastic polyurethane yarn (PU) to make the spiral Gr/MWCNTs’ composite yarn (SGCCY) with a core-sheath structure to improve its strain response range. From microstructure, mechanical, and electrical properties, the sensor is comprehensively evaluated based on sensing mechanism, sensitivity, and durability. The results show that the structure is embedded between Gr and MWCNTs. When the mass ratio of Gr to MWCNTs is 2:1, the ink conductivity is the best. The CCY, after six times of impregnation-drying treatment, is considered the best-wrapped yarn. SGCCY has good strain response characteristics between 0% and 200%, and the gauge factor (GF) can reach up to 30.77. It has a repeatable resistance change response at different rates and different strains. In addition, after multiple stretching releases, it still shows a stable electrical signal output and has good cycle stability. SGCCY can monitor large movements at joints such as fingers, wrists, and knees and small deformations such as breathing, vocalization, and swallowing. The core-sheath composite yarn prepared by the spiral wrapping method has excellent application prospects in intelligent wearables.