Simultaneous dyeing and functionalization of silk with three natural yellow dyes

Abstract

Three natural yellow dyes, namely Rheum emodi, Gardenia yellow and curcumin, were applied to the simultaneous dyeing and functionalization of silk. Their dyeing properties and functionalities as well as the effects of post-mordanting on the hue, color fastness and functionalities of dyeings were compared, and the correlations between the chemical structures and application characteristics of dyes were revealed. The three dyes exhibited large variations in dyeing and mordanting properties, and functionalities. Curcumin displayed the greatest coloring power. The uptake of Gardenia yellow was most sensitive to the pH of dyebath. Gardenia yellow and curcumin had much higher building-up ability than R. emodi with anthraquinone structures. Gardenia yellow possessed the highest fastness ratings, while curcumin and R. emodi showed poor wet rub fastness and wash fastness for staining. Curcumin imparted the highest antioxidant activity to silk because of its high adsorption and two phenolic hydroxyl groups in its structure and also gave the highest UV protection ability. Curcumin and R. emodi provided higher antibacterial activities than Gardenia yellow. The post-mordanting with ferrous and ferric salts exerted great influence on the color parameters, color fastness and UV protection ability of dyeings. This study points out that the common dyeing process of three natural yellow dyes can impart the color and functional properties to silk.