Dynamic Covalent Design of Keratin Sizes for Sustainable and Smart Yarn Coating

The development of green and reversible yarn coatings is essential for addressing the intelligent and sustainable weaving demands of the global textile industry. However, current sizing agents, primarily reliant on non-covalent interfacial interactions, encounter significant challenges, including insufficient mechanical properties, substantial desizing effluent production, and non-biodegradability. Herein, a green, smart, redox-responsive keratin-based sizing agent has been developed, inspired by the natural dynamic covalent behavior of disulfide bonds. By enhancing covalent disulfide switches at the size/yarn interface and within the sizing films while reducing random coil conformations, this keratin sizes demonstrates markedly improved adhesion to cotton fibers and increased film fracture energy, with enhancements of approximately 47% and 550%, respectively. Its reductive responsiveness facilitates easy removal, achieving up to 99.9% desizing efficiency at a bath ratio of 1:10 under ambient temperature conditions. The sulfhydryl-enrichment modification of feather keratins promotes reversible protein conformational changes and controllable covalent bonding during both sizing and desizing processes. Life cycle analysis (LCA) indicates an 87.3% reduction in CO2 emissions compared to conventional petroleum-based polyvinyl alcohol (PVA) sizes, alongside additional energy and water savings attributable to the simplified desizing process and mild operating conditions associated with the keratin-based agents.