Processing–structure–property relationships in keratin films prepared by solution casting and compression molding

Feather keratin represents a promising renewable feedstock for biopolymer films; however, its broader application has been limited by inadequate mechanical strength and barrier performance. In this study, the effects of sulfitolysis extraction conditions, crosslinker type and concentration, and processing method on the mechanical, barrier, and optical properties of keratin films were systematically investigated. Reducing sodium dodecyl sulfate concentration during extraction significantly enhanced film tensile strength, with improvements of up to 282%. Films plasticized with 20 wt% glycerol exhibited high flexibility, achieving elongation at break values exceeding 100% and reaching up to 133% when crosslinked with 1,4-butanediol diglycidyl ether (BDDE). Crosslinking with 10% formaldehyde or 10% BDDE reduced film solubility by ~80% and produced the highest tensile strength (4.28 MPa) while maintaining high ductility (86% elongation at break). Optimized keratin films demonstrated excellent oxygen-barrier performance, with oxygen permeability values of 13–16.6 × 10−6 cc·mm·m−2·day−1·Pa−1, comparable to polyethylene terephthalate and polyamide-6. Water vapor permeability remained below 2 × 10−3 g·mm·m−2·day−1·Pa−1, outperforming most keratin-based films reported in the literature. All films exhibited outstanding UV-blocking capability, with less than 0.4% transmittance in the 200–300 nm range. Comparative analysis revealed that solution-cast films displayed superior tensile properties and water resistance, whereas compression-molded films offered improved visual transparency. Overall, this work demonstrates that targeted control of extraction chemistry, crosslinking strategy, and processing route enables substantial performance enhancements in keratin films, advancing their potential as biobased packaging materials; however, further work is required to ensure compliance with food-contact safety regulations.