Affinity of Keratin Peptides for Cellulose and Lignin: A Fundamental Study toward Advanced Bio-Based Materials.

Keratin is a potential raw material to meet the growing demand for bio-based materials with special properties. Keratin can be obtained from feathers, a by-product from the poultry industry. One approach for keratin valorization is to use the protein to improve the properties of already existing cellulose and lignin-based materials to meet the requirements for replacing fossil-based plastics. To ensure a successful combination of keratin with lignocellulosic building blocks, keratin must have an affinity to these substrates. Hence, we used quartz crystal microbalance with a dissipation monitoring (QCM-D) technique to get a detailed understanding of the adsorption of keratin peptides onto lignocellulosic substrates and how the morphology of the substrate, pH, ionic strength, and keratin properties affected the adsorption. Keratin was fractionated from feathers with a scalable and environmentally friendly deep eutectic solvent process. The keratin fraction used in the adsorption studies consisted of different sized keratin peptides (about 1-4 kDa), which had adopted a random coil conformation as observed by circular dichroism (CD). Measuring keratin adsorption to different lignocellulosic substrates by QCM-D revealed a significant affinity of keratin peptides for lignin, both as smooth films and in the form of nanoparticles but only a weak interaction between cellulose and keratin. Systematic evaluation of the effect of surface, media, and protein properties enabled us to obtain a deeper understanding of the driving force for adsorption. Both the structure and size of the keratin peptides appeared to play an important role in its adsorption. The keratin-lignin combination is an attractive option for advanced material applications. For improved adsorption on cellulose, modifications of either keratin or cellulose would be required.

Ductile keratin films from deep eutectic solvent-fractionated feathers.

Feathers, an industrial by-product, are a valuable source of keratin that could be used, for example, in the preparation of films for biomedical and packaging applications. However, the utilisation of feather keratin requires scalable processes to convert feathers into a feasible keratin stream. This paper shows how deep eutectic solvent (DES) fractionated feathers could be converted into strong films. In the DES fractionation process, two keratin fractions with different molecular weights were obtained. The films made of the high molecular weight keratin fraction had better mechanical properties and stability against moisture than the films made of the low molecular weight keratin fraction. The strength properties were further improved by cross-linking the keratin with diglycidyl ether enabling the formation of a uniform keratin network, whereas glutaraldehyde did not show a clear cross-linking effect. These keratin films could be used, for example, in food packaging or medical applications such as wound care.

Green process to regenerate keratin from feathers with an aqueous deep eutectic solvent.

Poultry feathers, a source of keratin, are a significant side stream from the food industry, for which valorization is essential considering the circular economy aspects. For this, ecofriendly processes are the tools that allow the easy and feasible transformation of the feathers. Deep eutectic solvents (DESs) are generally considered as inexpensive, relatively simple, mild and environmentally friendly solvents which can dissolve proteins from protein-rich biomasses. In this work, feathers were processed with an aqueous DES to produce a uniform keratin feedstock. The proposed DES is composed of non-toxic sodium acetate and urea, with a small amount of water. After the DES treatment, water was used to dilute the DES components and regenerate the dissolved keratin. The processing conditions were optimized in terms of keratin yield and properties by varying the dissolution time from 2 h to 24 h and temperature from 80 °C to 100 °C. The yield of regenerated keratin was followed at different sodium acetate-urea molar ratios, and compared to the treatment performed with choline chloride-urea or 8 M urea as reference solvents. Sodium acetate-urea in the molar ratio of 1 : 2 at 100 °C and with 6 h dissolution time dissolved 86% of the feathers with a regenerated keratin yield of 45%. In the characterization of regenerated keratin, it was found that when the dissolution temperature was higher and the dissolution time longer, the disulfide and total sulfur content of feather keratin decreased, the range of molecular weights became wider, and some of the ordered secondary structure and crystallinity were lost.