Upcycling Coffee Silverskin Waste into Functional Textile Coatings: Evaluation on Cotton, Lyocell, Wool, and Silk

Agricultural and food by-products offer valuable opportunities for circular and bio-based innovation across sectors. In the textile industry, replacing fossil-based coatings with sustainable alternatives is increasingly urgent. This study evaluates the performance of a textile coating based on coffee silverskin (CS)—an abundant by-product of coffee roasting—applied to four natural fibre substrates: cotton, lyocell, wool, and silk. A formulation combining 60% CS sludge (8% solids), treated by wet ball milling, with an aliphatic polyester-polyurethane dispersion was applied via knife coating. Standardised tests assessed mechanical resistance, air permeability, colour fastness, moisture management, and water repellency, including contact angle and drop absorption analyses. Results revealed that all substrates were compatible with the CS-based coating, which reduced air permeability and increased hydrophobicity. Notably, silk showed the most significant functional enhancement, transitioning from hydrophilic to waterproof with increased durability—indicating strong potential for technical applications such as outerwear and performance textiles. Given the renewable origin of both the substrate and coating, this study highlights the feasibility of valorising agri-food waste in high-performance, bio-based textile systems. These findings demonstrate the potential of CS as a bio-based coating for technical textiles, supporting the development of high-performance and sustainable materials within the textile industry.