Regenerated cellulose fibers from coaxial wet spinning of alginate with excellent flame retardancy

Abstract

Environmentally friendly, sustainable, and widely available bio-based flame retardants provide an effective route for flameretardant functionalization of recycled cellulose materials. In this study, coaxial wet spinning is employed to encapsulate cellulose as the core with alginate as the shell. Coagulation in a Ca²⁺-containing bath enables simultaneous cellulose regeneration and in situ ionic crosslinking of sodium alginate (SA). With an optimized structural design, stable, all-bio-based core-sheath flame-retardant fibers (CAF) are constructed. The effects of sodium alginate concentration in the shell on fiber morphology, mechanical properties, and flame retardancy are systematically investigated. The resulting CAF markedly enhance flame retardancy while maintaining high mechanical properties, achieving a limiting oxygen index (LOI) of up to 32%. Compared with regenerated cellulose fibers (RCF), the peak heat release rate (PHRR) decreases by over 70%. Structural and thermal analyses reveal that the calcium alginate shell decomposes at the early stage of combustion to form a CaO/CaCO3-carbon composite protective layer, which effectively impedes heat and oxygen transfer and enables highly efficient flame retardancy. This work provides insights into the design and fabrication of high performance bio-based flame retardant regenerated cellulose fibers.