Phosphoric Acid-Based Dry–Wet Spinning of High-Performance Chitin Fibers: Chitosan Added for Enhanced Processability and Multifunctionality

Chitin is a nitrogen-rich polysaccharide extensively found as a key structural component in nature. Despite its noted advantages of being renewable, environmentally friendly, and readily biodegradable, scientific research and industrial applications have predominantly concentrated on its deacetylated derivative, chitosan. This preference arises from the well-known challenges associated with processing native chitin, which stem from its distinctive structural characteristics─specifically, extensive hydrogen bonding and high crystallinity. To address these limitations, we have devised a low-temperature dissolution methodology based on phosphoric acid, enabling the preparation of highly concentrated chitin solutions (up to 10 wt %). Utilizing this approach, we successfully fabricated regenerated chitin fibers (RChf) through dry–wet spinning techniques. The incorporation of an optimal proportion of chitosan proved to be effective in enhancing the spinnability of the dope and providing ionic cross-linking sites for postmodifications. The RCh fibers thus obtained show excellent mechanical properties, with tensile strength up to 330 ± 6.5 MPa (2.6 ± 0.11 cN/dtex), toughness of 17.0 MJ/m 3, and Young’s modulus of 19.5 ± 1.3 GPa. They also demonstrated an antibacterial rate of 99% and acquired flame retardancy (LOI = 32%) with a simple post-treatment with phytic acid. Given the vast quantities of chitin available as byproduct from seafood processing, such green and direct processing strategies hold promise for enhancing the utility and expanding the application scope of chitin-based materials across multiple sectors.