Upcycling Agricultural Waste for Functional Interfaces: Yellow Onion Skin-Derived Dyes for Cellulosic Materials

The growing environmental and health concerns associated with synthetic dyes have increased interest in natural alternatives. This study investigates the multifunctional properties of yellow onion skin extract as a sustainable dye source for cellulosic substrates, assessing the extract's functional properties beyond coloration. The extract was applied to premordanted cellulose nanofiber films (CNF) with a concentration of 2 g/L and knitted cotton fabric 0.125 g/L at 80 °C for 60 min, and its impact on UV protection, antioxidant properties, and dye stability was investigated. To enhance adsorption, biobased polyelectrolytes, including chitosan, tannic acid, and organic acids, were used as mordants and compared to metal mordants. Surface interactions between the cellulosic substrate and dye were studied using in situ monitoring to obtain data on the dyeing conditions for optimization. The dyed CNF films demonstrated excellent UV-shielding properties with up to 90% UV blocking and 82% DPPH radical scavenging activity, making them promising for protective packaging solutions. For cotton fabric, the dye concentration was low (0.125 g/L), resulting in relatively low color depth (K/S 1.33-5.59) with moderate (LF 3-5) fastness properties. Our study of KeratinoSens (OECD Test Guideline 442D equivalent) suggests a potential skin sensitizing effect of the yellow onion dye at higher concentrations. This needs further evaluation and studies. All together, these findings highlight the potential of yellow onion skin waste as a functional dye for applications in textiles and packaging that require enhanced surface properties.