Self-healing polyurethane/cellulose nanocrystal composite fibers with fatigue and aging resistance for smart wearable elastic yarns

With the rapid development of smart wearable devices, there is an increasing demand for materials that exhibit high strain, fatigue resistance, flexibility, and durability. Polyurethane (PU) fibers have gained attention due to their flexible molecular structure and adjustable formulations. However, the fatigue and aging resistance of traditional PU fibers are relatively weak, limiting their potential applications. To address this issue, this study presents a method for preparing PU-CNC self-healing composite fibers by incorporating environmentally friendly cellulose nanocrystals (CNC). It was found that the PU molecular chains create hydrogen bonds with the hydroxyl groups in the surface of CNC, forming a dynamic network with physical crosslinking that enhances the tensile strength and elongation, the self-healing ability, and the fatigue and aging resistance of PU-CNC composite fibers. Moreover, after fatigue and aging resistance tests, the mechanical characteristics of PU-CNC composite fibers are almost unchanged. When compared to PU fibers without CNC, the elongation at break and tensile strength of PU-1% CNC composite fibers increased by 33.92% and 17.93%, respectively. After the scratch test, the cracks on the surface of the self-healing of PU-1% CNC composite fibers disappeared, and the elongation at break and tensile strength increased by 57.18% and 128.02%, respectively. The flexibility and adaptability of this composite fiber provide a broad application prospect for the integration of flexible sensors and smart wearable devices, contributing to enhanced safety and durability in future smart devices.