Multi-crosslinked sodium alginate fibers with super-hydrophilicity, high strength, flame retardancy, and antibacterial properties.

Sodium alginate (SA) fibers are promising biomass-based material for sustainable applications, but their low limiting oxygen index (LOI) and lack of antibacterial properties restrict their use in flame-retardant protection. Traditional functionalization approaches often sacrifice mechanical properties, while enhancing strength alone typically fails to meet multifunctional requirements. To address this challenge, we developed a dual-crosslinked SA fiber combining calcium ion crosslinking and chemical crosslinking using hexamethylene diisocyanate (HDI) as the cross-linking agent in an aqueous solvent. Additionally, β-Cyclodextrin (β-CD) was employed to encapsulate cinnamaldehyde (CA) via its cavity structure, imparting flame-retardant and antibacterial properties. Through wet spinning, we successfully fabricated super-hydrophilic SA fibers with exceptional mechanical strength (breaking strength:3.07 cN/dtex), high flame retardancy (LOI:50.2-50.4 %), and antibacterial activity, while maintaining a water contact angle of 10.5°. These results demonstrate that the prepared SA fibers have great potential for use in advanced flame-retardant protective materials.