Mercerization to enhance flexibility and electromechanical stability of reduced graphene oxide cotton yarns

Graphene-based textiles combining reduced graphene oxide (RGO) nanosheets and cotton textiles such as cotton yarns (CYs) and cotton fabrics show promise as multifunctional electronic textiles (e-textiles) that can be fabricated at reasonable cost by a simple solution process. However, realizing e-textiles with high flexibility and excellent mechanical stability is still challenging. Here, we report a facile strategy for the fabrication of highly flexible and electromechanically stable graphene yarns composed of RGO nanosheets and CYs. More specifically, the fully conformal wrapping of RGO sheets onto the surface of CYs is achieved by combination of conventional mercerization and simple dipping. We optimized the surface chemistry, morphology, and elasticity of the CYs as substrates by conventional mercerization. Using the obtained mercerized CYs, which had a more hydrated surface, round shape, smooth morphology, and good elasticity, we successfully fabricated high-quality graphene yarns. We evaluated the electrical and electromechanical behavior of the RGO-coated mercerized cotton yarns for e-textile and wearable applications. They exhibited a good electrical conductivity of ∼1.0 S/cm, which is approximately 1,000 times that of RGO-coated CYs without mercerization, and exceptional flexibility and electromechanical stability under 50,000 bending cycles with a maximum bending radius of 0.5 mm. We successfully demonstrated the potential application of our novel graphene yarns as wearable electronics with a fire/flame sensor. We believe that our process offers an easy approach to improve the flexibility and electromechanical reliability of two-dimensional nanomaterial-based cotton textiles such as fiber, yarn, and fabric than those that might be expected in advanced e-textiles and wearable devices.