Innovative biobased cationic blue dye for covalently bonding with oxidized cotton: A sustainable strategy for durable, coloristic, and multifunctional cotton fabric

The textile industry faces a significant challenge in dyeing cotton fabrics due to their low affinity for anionic dyes, leading to substantial dye wastage and reliance on inorganic salts that harm the environment. This issue is particularly pressing for blue dyes, which are in high demand but less abundant in natural forms compared to red and yellow dyes. In response, this study presents an eco-friendly method for synthesizing a biobased cationic blue dye capable of forming covalent bonds with oxidized cotton, resulting in durable coloristic and multifunctional fabrics. Bio-based polylysine (PLL) was crosslinked with genipin (GNP) to produce a stable cationic blue dye (PLL-GNP). This dye was then applied to oxidized cotton fabric, achieving covalent bonding through a Schiff base reaction. The optimized conditions for the blue dye synthesis included pH 7, a mass ratio of PLL to GNP of 6:4, and a reaction time of 120 min. The oxidized cotton fabric exhibited acceptable adsorption capacity for the blue dye, achieving an exhaustion of 34 % and an adsorption quantity of 134 mg/g at a concentration of 4 g/L without the need for inorganic salts or alkalis. Under these conditions, the dyed cotton fabric exhibited a surface color depth ( K / S value) of 6.8. Color fastness tests revealed strong resistance to washing and rubbing, though lightfastness remains an area of concern. The application of PLL-GNP not only imparted a stable blue color but also enhanced the fabric’s functionality, providing UV protection (UPF 30), antioxidant activity over 75 %, and antibacterial activity against E . coli and S . aureus exceeding 95 %, all maintained even after multiple washes. This research addresses the urgent need for blue dyes in the textile industry, offering a sustainable and multifunctional dyeing solution that supports the broader adoption of biobased materials.