Industrially knittable CNT/cotton sheath-core yarns for smart textiles

Here, we demonstrate a process of developing strong and flexible CNT/Cotton conductive yarns. Highly spinnable millimeter tall CNT arrays produced by catalytic chemical vapor deposition were drawn into yarns and simultaneously wrapped over cotton yarn. The diameter and resistance of the CNT/Cotton yarn can be tuned for different applications and the lowest resistance obtained was 3.92 ohm/cm. The CNT/Cotton yarns were evaluated and compared in terms of tensile behavior and electrical conductivity. Integrating CNTs by wrapping over cotton yarn showed around 30% improvement in mechanical properties. This is further enhanced by the application of a polyurethane binder and prevents the delamination of CNTs from the yarns during mechanical strain. Scanning electron microscopic (SEM) images show uniform wrapping of the CNTs. The produced yarn can withstand 1000 loading cycles with a very small decrease in conductivity. The yarn was used to demonstrate powering a LED. The CNT/Cotton sheath-core yarn was also directly supplied to a whole garment industrial knitting machine to form a three-dimensional textile. The knitted structures showed very stable strain sensing properties and can accurately track the movement of a finger. When voltage is applied, the knitted smart textiles shows rapid heat generation and uniform distribution of heat. It was found that at 3V the knitted structure produced a temperature higher than body core temperature within 15 seconds. The developed yarn has the potential for the production of smart textiles on an industrial scale.