Fully Bio‐Based Keratin/Cellulose Nanofiber Composite Foams With Intrinsic Flame Retardancy and Thermal Insulation

Keratin (WK), TEMPO‐oxidized cellulose nanofibers (TOCNF), and phytic acid (PA) were used to successfully fabricate fully bio‐based KCP composite foams by regulating composition ratios and freezing methods. The effects of composition ratio and freezing conditions on the microstructure, thermal insulation, flame retardancy, and mechanical properties were systematically investigated. Structural characterization confirmed the formation of a porous network, and the freezing strategy significantly influenced pore morphology. Infrared thermal imaging demonstrated that, compared with pure polyurethane foam, KCP foams exhibited superior thermal insulation performance. Vertical burning tests showed that all samples possessed self‐extinguishing behavior, with after‐flame and after‐glow times of 0 s. The limiting oxygen index (LOI) values ranged from 29% to 34%, indicating flame‐retardant performance superior to the oxygen concentration in ambient air. Although increasing the keratin content did not significantly enhance mechanical strength, it influenced combustion behavior and postburning structural integrity. Overall, the developed KCP foam provides a sustainable and environmentally friendly alternative to petroleum‐based insulation materials, combining thermal insulation and flame‐retardant properties with potential for further mechanical optimization.