Research on overdyeing process of indigo and turmeric on nylon knitted fabrics

This study investigated the overdyeing process of nylon knitted fabrics using two natural plant dyes-indigo and turmeric-to address the high pollution associated with synthetic dyes and the limited color gamut of natural dyes. Through single-factor experiments, the dyeing parameters were optimized to achieve yellow-green and blue-green hues. The dyeing performance, color fastness, and antibacterial properties of the dyed fabrics were evaluated. The optimal conditions for yellow-green shades were: indigo 5 g/L, glucose 10 g/L, NaOH 1 g/L, liquor ratio 1:50, reduction at 60 °C for 30 min, oxidation at room temperature for 30 min; followed by turmeric 1.2 g/L, liquor ratio 1:60, dyeing at 80 °C for 20 min. For blue-green shades: indigo 10 g/L, turmeric 0.8 g/L, dyeing at 50 °C, with other parameters identical. Both overdyed fabrics exhibited color fastness of grade 4 or higher, meeting apparel requirements. Antibacterial rates against Staphylococcus aureus and Escherichia coli reached 99% and 98%, respectively. These results confirm the feasibility of applying natural plant dyes to nylon fabrics and provide a reference for sustainable textile dyeing.