Self-healing, highly stretchable, and 3D printable thiol-functionalized cellulose nanofibers/waterborne polyurethane composites for flexible electronic monitoring

Abstract

The development of conductive materials with high mechanical resilience and effective self-healing capabilities is essential for flexible electronic monitoring. However, simultaneously achieving superior mechanical properties and self-healing ability in materials remains a significant challenge. In this study, a novel eco-friendly, 3D printable waterborne polyurethane composite (CSPU) was synthesized by incorporating waterborne polyurethane with thiol-functionalized cellulose nanofiber. The resulting CSPU composites exhibit excellent mechanical strength and ductility, showing an elongation at break of up to 1300 % and a stress of 5.5 MPa. Moreover, the composite achieves efficient self-healing after UV irradiation, with both strain and stress recovery reaching nearly 100 % within 1.5 h. With the CSPU composite’s excellent printability, a flexible conductive composite sensor with specific shape is prepared by spraying an ultrasonic dispersion of cellulose nanofiber and carbon nanotubes onto the 3D printed CSPU composites, followed by drying process. The flexible sensor demonstrates excellent self-healing capabilities, flexible, reliability, and good electrical signal detection capabilities, enabling accurate monitoring various human motions, such as the bending of human fingers. These exceptional properties position it as a highly promising candidate for applications in flexible electronic monitoring, medical health, human–machine interfaces, and beyond.