Unfolding and refolding pathways of feather keratin as a function of temperature in ultrasound-assisted alkaline hydrolysis

This study reveals temperature-dependent pathways in the regeneration of keratin from duck feathers via ultrasound-assisted alkaline hydrolysis, establishing direct links between molecular transformations and resulting material morphologies. By systematically varying the hydrolysis temperature from 25 °C to 85 °C, we identify a critical threshold around 55 °C that governs keratin's unfolding and refolding behavior. At lower temperatures (≤55 °C), keratin retains its native disulfide linkages and regenerates into fibrous structures resembling feather morphology. Above this threshold, extensive cleavage and reformation of disulfide bonds induce supramolecular reorganization, yielding uniform keratin microspheres with enhanced thermal stability and distinct Raman signatures. Comprehensive characterization (ATR-IR, Raman, solid-state NMR, XRD, SEM, TGA, DSC) provides unprecedented insights into how temperature and sonochemical activation modulate protein structure at both molecular and mesoscopic scales. These findings establish a chemistry-based design principle for tailoring keratin into functional biomaterials with tunable properties, enabling scalable and sustainable approaches to bioplastics, composites, and biointerfaces. • This work provides an innovative approach to keratin recovery from poultry feather waste. • Ultrasound-assisted hydrolysis reduces processing time and energy consumption. • The process enables selective recovery of keratin in different structural forms. • A critical temperature threshold (55 °C) occurs, where keratin transitions in terms of shape and composition.