One of the most underutilized protein sources is the feather side stream of the poultry industry. Feathers are mostly either burned, buried in the landfills or recycled as poorly digestible feed leaving about 12.6 million metric tons of keratin to be used in higher value products. To enable the value addition for feather keratin, the most feasible and suitable processing methods and applications should be identified. This kind of identification requires a deep understanding of feather keratin and how its structure and interactions are linked to its properties. The aim of this study was to understand how feathers could be converted into utilizable keratin fractions and evaluate their potential as building blocks for future materials. To produce molecular keratin, feathers were dissolved in an aqueous deep eutectic solvent (DES). It was found that the DES used was able to disturb the interactions within the feather keratin, cleave the disulfide bonds in its structure, alter the conformation, and partially break down the polypeptide backbone, and that the molecular weight of the keratin played an important role in its solubility. Film structures were prepared from molecular keratin to study the physical properties and reactivity of keratin. The conformation and molecular weight of keratin, as well as the addition of plasticizers and cross-linkers, had determining roles in the mechanical properties and water sensitivity of the films. To compare the used DES process to a mechanical treatment, a simpler alkaline pre-treatment combined with milling was carried out to produce fibrous keratin. A comparison of films made of molecular and fibrous keratin showed that fibrous keratin is suitable in applications in which transparency, good barrier properties, or reactivity are not required such as composites while molecular keratin is suitable in various applications. To evaluate the possibility to combine keratin with other bio-based materials, the adsorption of keratin peptides obtained from the used DES process on cellulose and lignin substrates was studied. The interactions between cellulose and keratin peptides were found to be weak, while on lignin substrates keratin peptides had high adsorption. The structural properties of keratin including the amino acid content, molecular weight, and random coil conformation together with the negative net charge of lignin surfaces were demonstrated to be the determining factors for the adsorption behavior.

Keratin building blocks from feathers for material applications

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