Upcycling Keratin‐Based Textile Waste Into High‐Performance Hybrid Fibers Via Tuning the Interfacial Interactions

Keratin‐based textile waste represents an underutilized protein‐rich feedstock, but its conversion into regenerated fibers remains challenging because of its low mechanical strength, poor spinnability, and limited compatibility with other biopolymers. In this work, we applied dry‐jet wet spinning to produce cellulose/keratin hybrid fibers using keratin extracted from textile waste. During extraction, keratin was separated into two fractions, and their chemical composition, secondary structure, and molecular weight were thoroughly analyzed to understand their differences in fiber formation. Hybrid fiber with a cellulose/keratin ratio of 70/30 was continuously produced from the high‐molecular weight keratin fraction using multi‐filament spinning, achieving a linear density of 1.2 dtex (corresponding diameter of 11 µm) and tenacity of 35–40 cN/tex (corresponding tensile strength of ca. 480–560 MPa). More interestingly, the fibers retain their mechanical strength in a wet state, which is rarely achieved for polysaccharide and protein‐based fibers. Additionally, the hybrid fibers exhibit higher hydrophobicity and lower fibrillation tendency compared to pure cellulose fibers. This remarkable approach demonstrates a dual advantage by valorizing keratin waste into valuable resources while simultaneously enabling the tailored tuning of cellulose fiber properties.