Highly conductive lignin-derived carbon nanotube/copper yarns with excellent electrothermal performance

Traditional carbon nanotube (CNT) synthesis often uses petroleum-based materials, while biomass-derived CNTs are more environmentally friendly. Carbon nanotube yarns (CNTYs), as macroscopic forms of CNTs, combine good electrical conductivity and lightness, reducing the risk of fiber breakage and holding great potential in flexible electrothermal devices. However, structural defects such as carbon nanotube entanglement and inter-tube gaps restrict biomass-based carbon nanotube yarns, and their performance potential has not been fully realized. This study synthesized a lignin-derived carbon nanotube yarn (LCNTY) using the floating catalytic chemical vapor deposition (FCCVD) method. Using a multi-scale strategy with stretching densification, plasma treatment, and metal loading, we created a “structure-interface-deposition” system to make flexible, highly conductive lignin-derived CNT/copper yarn. The electrical conductivity of the prepared lignin-derived carbon nanotube yarn increased from 2.30 × 10⁵ S m⁻¹ to 1.20 × 10⁶ S m⁻¹ after being stretched and densified with the assistance of chlorosulfonic acid (CSA), and to 4.46 × 10⁶ S m⁻¹ after the surface was functionalized by oxygen plasma and copper electroplating was carried out, which is superior to most carbon nanotube yarns. In electrothermal tests, the lignin-derived carbon nanotube/copper yarn obtained through a series of modifications reached 146.2 °C in 2 s at 2.2 V and stayed stable for over 1000 s. This work provides valuable insights into the potential of flexible biomass-derived carbon nanotube/metal yarns in electrothermal applications.