Nanochitins of Varying Aspect Ratio and Properties of Microfibers Produced by Interfacial Complexation with Seaweed Alginate

We introduce chitin nanofibers, nanochitin (ChNF), the cationic groups of which electrostatically complex in aqueous media with the anionic groups of a polyanion, seaweed alginate (SA). This allows the formation of continuous microfibers after drawing contacting suspensions. We elucidate the effect of the nanofiber aspect ratio (15, 25, and >60) on the mechanical performance of the composite microfibers after considering variables such as concentration, pH, and drawing rate. An automatic collector facilitated a constant spinning velocity of 30 mm/s upon interfacial complexation from aqueous media (using 0.3 to 1 wt % as mass fraction for each component and a pH between 4 and 7). The composite microfibers showed a core-shell structure in which ChNFs were preferentially axially aligned in the center and more randomly oriented in the shell. The degree of ChNF alignment in the core increased with the aspect ratio, as resolved by WAXS diffractograms. Consequently, ChNF with the largest aspect ratio (>60) was readily spun into microfibers that displayed the highest Young's modulus (4.5 GPa), almost double that measured for the shortest ChNF. The latter, however, presented the highest strain and flexibility and allowed continuous fiber spinning. Distinctively, tensile tests revealed mechanically stable microfibers even in wet conditions, with a strength loss of less than 50% and strain gains of up to 35%. The amino and carboxyl groups in the microfibers offer possibilities for functionalization, expanding their potential beyond that related to wound healing and antibacterial applications. Overall, we provide a new perspective toward dry spinning via interfacial complexation of biobased components and the effect of a particle's morphology on the detailed structuring of microfibers, which display a particular assembly that is discussed here for the first time.