A facile strategy for fabricating high-strength fireproof biomass alginate-based composite fiber

Calcium alginate biomass fibers are ideal for eco-friendly flame-retardant textiles, yet poor mechanical strength and persistent smoldering restrict their thermal protective use and commercial promotion. To address these limitations, a dual-reinforcement strategy was proposed by incorporating cellulose nanocrystals (CNC) as rigid nano-reinforcements and seaweed-derived polypeptide (SDP) as a multifunctional crosslinker to prepare composite fibers via wet-spinning technique. Hydrogen bonding among these components strengthened mechanical performance, and nitrogen-rich SDP chains inhibited sustained smoldering and boosted flame retardancy. Notably, composite fibers containing 0.02 wt% CNC and 1.00 wt% SDP achieved improved mechanical properties and superior flame retardancy, reaching a UL-94 V-0 rating with thermal protective performance above 2523 kW·sec·m^-2. Combustion analysis verified that the composite fiber presented low heat and smoke release with negligible toxic gas emission, confirming its excellent fire safety and applicability to personal thermal protection. Furthermore, analysis of char residues and pyrolysis products revealed the intrinsic flame-retardant mechanism where inorganic calcium salts formed dense barriers and non-flammable pyrolytic gases diluted flammable surroundings, and their combined effect isolated heat and oxygen to terminate combustion. This work offered an efficient strategy to improve the mechanical strength and flame resistance of biomass alginate fibers, making them promising high-performance textile candidates.