Use and valorization of wool waste - Keratin extraction and its applications as a biopolymer

Recovery and valorization of biopolymers obtained from cheap and renewable sources, such as keratin from wool, may have an important environmental and economic impact. Keratins are one of the most abundant classes of non-food proteins, being the major component of skin (soft keratins) and of nails, claws, hair, horn, feathers, and scales (hard keratins) of vertebrates, but above all, animal textile fibers. Pure keratin constitutes up to 90% by weight of wool. Keratin matter from farm breeding and butchery has been considered a rather complicated disposal challenge, despite its important and interesting characteristics, since burning for fuel is inefficient and polluting due to its high sulphur content (3-4% wt). The Food and Agriculture Organization of the United Nations has published data showing that the annual production quantity of keratin, primarily from livestock, has exceeded 10 million tonnes since 2012. The annual world production of keratin, derived mainly from livestock, was 11.82 million tonnes in 2020. The total amount of keratins has been estimated worldwide to be more than 12 million tonnes per year. Wool is an important and accessible bio-source of keratin. The wool obtained from sheep breeds is categorized into carpet grade (<50 μm fibre diameter) and coarse type of wool (>50 μm fibre diameter).