Autogenous Cross-Linking of Recycled Keratin from Poultry-Feather Waste to Hydrogels for Plant-Growth Media

The global rise in atmospheric temperature is leading to an increasing spread of semi-arid and arid regions and is accompanied by a deterioration of arable land. Polymers can help in a number of ways, but they must not be a burden to the environment. In this context, we present herein a method by which goose feathers, representative of keratin waste in general, can be transformed into hydrogels for use as a plant growth medium. The treatment of shredded feathers in Na₂S solution at ambient conditions dissolves approx. 80% of the keratin within 30 min. During evaporation, the thiol groups of cysteine reoxidise to disulphide bridges. Additionally, the protein chains form β-sheets. Both act as cross-links that enables the formation of gels. The drying conditions were found to be crucial as slower evaporation affords gels with higher degrees of swelling at the cost of reduced gel yields. The cress germination test indicated the absence of toxic substances in the gel, which strongly adheres to the roots. Thereby, the plants are protected from drought stress as long as the gel still contains moisture.