Optimization of natural anthocyanin efficient extracting from purple sweet potato for silk fabric dyeing

The main objective of this study is to extract natural colorant anthocyanin from purple sweet potato powder via ultrasound-assisted ammonium sulfate/ethanol aqueous two-phase system, and this method can avoid the serious environment pollution during the preparation and use process of synthetic dye, reduce the solvent and simplify the abstraction procedures. The extracted natural colorant anthocyanin was used to dye silk fabric in a relatively ecological approach. Based on the single-factor extracting experiment, central composite design-response surface methodology was employed to optimize the ultrasound-assisted aqueous two-phase system extracting conditions including ultrasound temperature, ultrasound time and dosage of purple sweet potato powder. The binomial model was highly significant and applied to fit the experimental data, due to its higher related coefficient. Via optimizing, a dosage of 1.60 g purple sweet potato powder was dispersed in ultrasound bath at 52.48 °C for 48.19 min. In the case of extracting conditions, 191.09 mg.L−1 natural colorant anthocyanin was produced in the upper ethanol-rich phase of the aqueous two-phase system. The color strength value of the silk fabric treated with mordant dyeing method was 4.5, and increased by 40.6% compared to that of the direct dyeing method. The dry and wet rubbing fastness using mordant dyeing method were 4–5 and 4 grade, respectively. The change and stain washing fastness using mordant dyeing method were 3–4 and 4–5 grade, respectively. This study demonstrates that developed natural colorant extracted from plant could be successfully employed as an effective and eco-friendly alternative cleaner to replace synthetic colorant gradually using in textile dyeing industry.