Abstract
A continuous and scalable method for the wet spinning of cellulose nanofibrils (CNFs) is introduced in a core/shell configuration. Control on the interfacial interactions was possible by the choice of the shell material and coagulant, as demonstrated here with guar gum (GG) and cellulose acetate (CA). Upon coagulation in acetone, ethanol, or water, GG and CA formed supporting polymer shells that interacted to different degrees with the CNF core. Coagulation rate was shown to markedly influence the CNF orientation in the filament and, as a result, its mechanical strength. The fastest coagulation noted for the CNF/GG core/shell system in acetone led to an orientation index of ∼0.55 (Herman’s orientation parameter of 0.40), Young’s modulus of ∼2.1 GPa, a tensile strength of ∼70 MPa, and a tenacity of ∼8 cN/tex. The system that underwent the slowest coagulation rate (CNF/GG in ethanol) displayed a limited CNF orientation but achieved an intermediate level of mechanical resistance, owing to the strong core/shell interfacial affinity. By using CA as the supporting shell, it was possible to spin CNF into filaments with high water absorption capacity (43 g water/g dry filament). This was explained by the fact that water (used as the coagulant for CA) limited the densification of the CNF core structure, yielding filaments with high accessible area and pore density.
Highlights
Fibers form the basis of a multitude of materials that capitalize on their high aspect ratio and anisotropy
The orientation of the cellulose nanofibrils (CNFs) component in the core/shell filaments spun at different coagulation conditions was studied by 2D-WAXD, assuming that the orientation of the cellulose crystallites provides an indication of the fibril orientation in a filament
The 2D-WAXD diffractograms for CNF-containing filaments (Figure 2a) consist of rings with radii corresponding to the scattering vector originated from the cellulose crystal planes 200 as well as 110 and 11̅0 merged
Summary
Fibers form the basis of a multitude of materials that capitalize on their high aspect ratio and anisotropy (different properties in the axial and radial directions). When changing the shell material from CA to GG, while keeping ethanol as the coagulant, the Young modulus of the filament (initial slope of the stress−strain curve), tensile strength (maximum stress per cross-sectional area), and tenacity (maximum stress per coarseness) increased from 907 ± 85 to 1313 ± 122 MPa, from 29.9 ± 7.5 to 38.0 ± 9.9 MPa, and from 4.01 ± 0.41 to 6.30 ± 0.90 cN/tex, respectively This can be explained by the stronger affinity between CNF and GG, arising from the larger number of hydroxyl groups available for hydrogen bonding with cellulose. The highest wet tensile strength among the core/shell filaments was for ethanol-coagulated CNF/CA and acetonecoagulated CNF/GG Acetone coagulates CNF and GG into a structure which is stronger when dry and maintains its strength when exposed to water
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