Enhanced Electrical and Thermal Conductivity of Waterborne Polyurethane Composites by Simultaneously Incorporating Cellulose Nanofibers and Carbon Nanotubes

Abstract Flexible wearable electronic devices, which integrate flexible electronics with wearable technology, have attracted widespread attention in recent years. Conductive polymer composites prepared by combining polymer matrices with conductive fillers offer advantages such as facile processability, favorable mechanical properties, and tunable characteristics, making them highly suitable for applications in flexible electronics. In this study, waterborne polyurethane/carbon nanotube conductive composites were prepared using carboxylated carbon nanotubes (cMWCNTs) and pristine multi‐walled carbon nanotubes (MWCNTs), with carboxylated cellulose nanofibers (CNFs) introduced for performance optimization. The hydrophobic C─H bonds on the CNFs surface can form strong π–π interactions with carbon atoms on the MWCNTs surface, leading to mutual repulsion between CNFs and MWCNTs. Acting as a “bridge,” CNFs effectively prevent MWCNTs aggregation through steric hindrance and physical entanglement, while the large specific surface area and intrinsic conductivity of MWCNTs enhance the stability of the CNFs network. Together, they construct a complementary three‐dimensional conductive network, improving the uniformity of dispersion. Through this synergistic effect, the fibrous CNFs network suppresses MWCNTs agglomeration and provides long‐range conductive pathways, whereas short‐range MWCNTs junctions reduce interfacial resistance. Consequently, electrons and phonons migrate rapidly along continuous pathways, simultaneously enhancing both electrical and thermal conductivity. Experimental results demonstrate that the composites exhibit improved mechanical strength (up to 25.81 MPa), electrical conductivity, thermal conductivity (0.424 W/(m·K)), and dielectric properties. These findings highlight the potential of CNFs incorporation in the development of high‐performance functional materials for flexible electronic devices.