During the last decades, cellulose nanofibres (CNFs) and cellulose nanocrystals (CNCs) have been widely incorporated as components in various material concepts, not only to replace synthetic materials but also since they provide unique properties related to their plant-based origin. The mechanical performance is strongly related to the hierarchical structure of the material concepts, which becomes specifically apparent for filaments produced from CNF or CNC, where the relation between nanoscale alignment in the direction of filaments can be directly coupled to the strength and stiffness. However, it has also been shown that filaments with a highly aligned nanoscale structure have an elastic-plastic stress-strain behavior and show recovery of the initial elastic modulus after being strained into the plastic region. <br/> <br/>We hypothesize that this stress-strain behavior could be related to a mesoscale structuring resulting from nanoscale self-assembly during consolidation and drying. By using a flow-focusing technique is possible to perform sol-gel spinning of filaments at low concentration (&lt;0.3% wt) with a high initial degree of CNF alignment. The resulting gel thread was studied concerning time-dependent internal restructuring during evaporative drying using scanning Small Angle X-ray Scattering (SAXS). These measurements were supplemented by cross polarizer imaging, making use of the fact that the CNF is birefringent. The results indicate the appearance of a well-defined internal structural organization of the CNF within the filament.

Mesoscale structuring of cellulose nanofibers induced by alignment and drying

ACS Spring 2022

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