Keratin bionanocomposite film cross-linked and reinforced with functionalized cellulose nanocrystals (fCNCs)

• Keratin was extracted from waste chicken feathers via a green method. • Functionalized CNCs and glutaraldehyde reinforced and cross-linked keratin. • fCNCs enhanced the tensile strength, modulus, and hydrophobicity of the keratin film. • The film showed superior mechanical performances containing 3 wt. % fCNCs. • The biocomposite potentially offers a sustainable route for bio-based packaging application. Chicken feathers are produced in large quantities worldwide as waste, and millions of tons are globally discarded each year. This issue creates significant environmental and disposal challenges. Some methods used to extract and enhance the properties of keratin from chicken feathers often involve polluting chemical processes, and the extracted polymer frequently has poor mechanical properties. In this study, keratin extracted from waste poultry feathers was valorized to develop sustainable bionanocomposite films. Keratin was first extracted through a green reduction process using l -cysteine, followed by chemical crosslinking with glutaraldehyde and reinforcement with amino-functionalized cellulose nanocrystals (fCNCs). To obtain fCNCs, pristine CNCs were modified with 3-aminopropyltriethoxysilane (APTES) to introduce surface amine groups for covalent bonding with keratin chains. The prepared cross-linked and reinforced films were characterized in terms of morphology, water contact angle, water uptake, water vapor permeability (WVP), and mechanical performance. FTIR analysis confirmed the successful functionalization of CNCs and the formation of imine ( C = N ) linkages, indicating covalent bonding between keratin and fCNCs. Mechanical testing revealed that the incorporation of 3 wt.% CNCs enhanced the tensile strength from 6 to 13 MPa, while 3 wt.% fCNCs further improved it to 21.4 MPa with an elastic modulus of 892 MPa and elongation at break of 30 %, confirming superior stress-transfer efficiency . Moreover, the addition of fCNCs increased the water contact angle from 58° to 87°, and reduced water uptake (35→18 %) and WVP (8.2→0.7 g m⁻² s⁻¹ Pa⁻¹), demonstrating enhanced hydrophobicity and barrier performance . These results indicate that fCNC-reinforced keratin films are promising candidates for eco-friendly packaging and biomedical applications.