Wet spinning of chitin nanowhiskers: Effects of electrolyte composition in coagulation baths on mechanical properties and nanowhisker orientation

Fibers composed solely of chitin nanowhiskers (ChNWs) with extreme uniaxial orientation can be successfully wet-spun into coagulation baths containing 70% ethanol and various types of electrolytes (LiCl, HCl, NaCl, and MgSO4) with ionic strengths (J) of 0.075-0.3. The obtained fibers exhibited high ChNW orientation with degrees of orientation (S) ranging from 0.77 to 0.96. Fibers produced using NaCl-containing coagulation baths contained residual NaCl crystals that were subsequently removed by rinsing. In contrast, LiCl and MgSO4, which originated from the corresponding baths and similarly remained within the fibers, did not crystallize due to hygroscopic deliquescence and the adaptation of SO42- ions for potential ionic crosslinking, respectively. Spinning with LiCl-containing baths yielded fibers with maximum Young's modulus, stress at break, and strain at break of 7.9 +/- 0.6 GPa, 58.8 MPa, and 1.13%, respectively. These mechanical properties of the unwashed fibers improved with J, while washing out the residual electrolytes and subsequent drying led to a decrease in the Young's modulus and an increase in the stress at break and strain at break. An increase in S was observed only in the fibers obtained using baths with J >= 0.3. A schematic procedure showing a preparation of chitin nanowhiskers from crab shell alpha-chitin and subsequent wet spinning into chitin nanowhisker fibers. image