Wool keratin-based nanofibres for active filtration of air and water

Large amount of protein wastes, such as fibre by-products from the wool textile industry and poor quality wools from stock-farming and butchery, are currently disposed of. Their pooling and processing would allow the production of innovative bio-plastics suitable for novel large-scale uses (compostable films for agriculture and packaging, filaments for textiles, sanitation and filtration). Since it is known that keratinous materials can absorb toxic substances such as heavy-metal ions, formaldehyde and other hazardous VOCs (volatile organic compounds), applications can also be envisaged in water purification and air cleaning. However, the poor mechanical properties of keratin regenerated from wool restrict processing and practical applications. Therefore, blending keratin with appropriate polymers with better structural properties is a way to overcome the aforementioned problems. In the present work, keratin was extracted from wool and blended with polyamide 6 in formic acid as the common solvent, in order to obtain blend solutions suitable for nanofibre production by electrospinning. Viscosity of the blend solutions decreased with increasing the keratin content, while electrical conductivity (of 2 mS/cm) did not change significantly. Electrospinning produced very thin nanofibres, in the range from 70 to 300 nm, with mean diameter of about 150 nm. The adsorption of heavy metal ions from water was evaluated by immersion of keratin/PA6 nanofibre mats in an aqueous solution of Cr(3+) and compared with the films obtained by casting from the same solution. For the nanofibre non-wovens the adsorption capacity slightly increased with increasing the keratin content. That of the nanofibre mats was at least one order of magnitude greater than the films obtained by casting. Moreover, whilst the physical efficiency of nanofibre-based filters is well known, the formaldehyde adsorption of protein nanofibres was studied in order to test their suitability for application in "chemical" air cleaning.