Wet spinning of cellulose nanowhiskers; fiber yarns obtained only from colloidal cellulose crystals

Wet spinning of aqueous cellulose nanowhisker suspensions successfully yielded fibers comprising only cellulose I crystals. By increasing the CNW concentration up to 13 wt%, the degree of orientation of the nanowhiskers and the Young's modulus of the fibers were increased up to S = 0.92 and ca. 10 GPa, respectively. The Young's modulus and stress at break decreased with an increase in electrolyte concentration in the coagulation bath; however, they recovered upon washing the fibers with water and subsequent drying. The maximum Young's modulus and stress at break values were 18.6 +/- 2.4 GPa and 109 +/- 3.8 MPa for the cotton nanowhisker fibers and 18.1 +/- 2.7 GPa and 141 +/- 19.5 MPa for the tunicin nanowhisker fibers, respectively. The higher crystal integrity and higher aspect ratio of the tunicin nanowhiskers as compared with those of the cotton nanowhiskers resulted in higher mechanical properties. The carboxylated nanowhiskers obtained by TEMPO-mediated surface oxidation yielded fibers with higher mechanical properties than those of sulfated nanowhisker fibers upon spinning, probably due to the formation of hydrogen bonds between the nanowhiskers.