Dry-jet wet spinning-mediated microstructural engineering for improving mechanical properties of pure chitosan fibers

Chitosan-based bio-fibers demonstrate significant application potential in the fields of biomedicine and functional textiles, owing to their advantages such as excellent biocompatibility, antibacterial activity, renewability, and biodegradability. However, the strong intermolecular hydrogen bonding of chitosan hinders the formation of an ideal microstructure with high orientation, high crystallinity, and minimal defects under conventional wet-spinning conditions, resulting in unsatisfactory mechanical properties of chitosan fibers. To address this limitation, an air gap was introduced into the traditional wet-spinning process, establishing a dry-jet wet spinning approach. By controlling the drawing step within the air gap, pre-orientation of chitosan molecular chains was achieved prior to coagulation, thereby optimizing the fiber microstructure. Compared to wet-spun fibers, the dry-jet wet spun chitosan fibers exhibit a smoother and denser surface with markedly fewer microvoid defects. Both crystallinity and orientation are significantly enhanced, with the degree of orientation increasing with the draw ratio. At a spinneret draw ratio of 1.6, the dry-jet wet spun chitosan fiber achieved a mechanical strength of 2.13 cN/dtex, representing a substantial improvement over the wet-spun counterpart. This dry-jet wet spinning strategy offers an effective technical route for the large-scale production of high-performance chitosan fibers.