High-strength and functional nanocellulose filaments made by direct wet spinning from low concentration suspensions

Continuous filaments obtained through the wet spinning of nanocellulose have promising mechanical properties with sustainable features. To guarantee proper spinnability for wet spinning, freshly made cellulose nanofibril (CNF) suspension needs to be concentrated to have a concentration above 1 wt%, resulting in energy- and time-consuming, and inferior mechanical properties of the final filaments owing to decreasing the CNF alignment against shear flows. In this study, a CNF spinning suspension at a low concentration (0.4 wt%) can be used right after the fibrillation process without further treatments. The effects of the concentration and re-concentrating process are studied by carefully characterizing the rheological behavior and filament solidification processes, which provides more fundamental understandings on the spinnability and CNF network formation of such colloidal CNF suspensions. Combined with a post stretching process, the final dried CNF filaments have superior mechanical properties with Young's modulus and tensile strength of 35 GPa and 567 MPa, surpassing most literature data. Moreover, different functional particles can be easily incorporated to prepare functional filaments. With facile preparation and superior properties, these CNF filaments may be suitable for advanced composite filler and special textile applications.