Wet-spinning of cellulose nanofibril hydrogels

Filaments were produced from cellulose nanofibrils (CNF) through wet-spinning for developments toward renewable fibre-based materials, such as absorbents or fibre-reinforced composites. The possibility to spin long filaments (i.e., spinnability) and resulting filament quality were related with the rheological behaviour of the CNF hydrogels used as precursors. A prototype wet-spinning line was developed for high-throughput filament production by co-extrusion with a supporting biopolymer shell around the CNF core. This system was also employed to spin absorbent filaments from CNF in combination with a shell that had limited compatibility with cellulose and coagulated effectively in aqueous media. The moisture sorption capacity was also increased by increasing the CNF surface charge, which also enhanced fibril alignment during filament formation. Filament mechanical integrity in wet conditions was improved through hydrophobic coating and interfibrillar crosslinking. The results highlight the use of wet-spinning as a simple and versatile approach to generate tuneable filaments from cellulose, an abundant bioresource. This will eventually enable the adoption of renewable options in applications that currently rely on fibres made from fossil carbon.