Dyeing And Functionalization Of Silk Fabric With Yellow Natural Dyes

The application of natural dyes has a long history. Although natural dyes are inferior to synthetic dyes in terms of stability and color fastness, they have been renewed emphasis on and adopted for the development of functional textile due to their superior performance such as biocompatible, antibacterial, anti-inflammatory, non-toxic and biodegradable. Silk is regarded as a textile material of superior quality owing to its excellent performance and gorgeous appearance. Moreover, silk has also found a wide range of applications as a biomaterial in the medical field due to its remarkable mechanical performance, biocompatibility and controlled degradability. With all its advantages, silk fiber is by no means without its limitations which suffers from some shortcomings such as yellowing, instability to light, poor UV protection capability and poor antimicrobial activity. These defects inevitably restrict the application of silk fiber. For this reason, in the present paper, the application of natural dyes onto silk and the antioxidant ability, antibacterial ability and UV-protection were investigated.In this paper, the dyeing and functional properties of three natural yellow dyes(Rheum emodi, Gardenia yellow, and curcumin) applied to silk were compared and the correlations between the chemical structures and application characteristics of dyes were attempted to reveal. The variations of color shade, fastness and functionality before and after mordanting were investigated. Color fixation and molecule modification methods were introduced to surmount the deficiencies of poor fastness and solubility of curcumin when dyed to silk and the effects on the functionalities were analyzed and valued. By these basic research, the important conclusions were drawn as follows:(1) Curcumin had the greatest coloring power and good building-up ability compared with Rheum emodi and Gardenia yellow. Gardenia yellow displayed the highest building-up ability and p H-sensitive uptake characteristic. Gardenia yellow had the highest fastness ratings, curcumin and Rheum emodi had disadvantages in wet rub fastness, wash fastness for staining, and light fastness. All the three dyes had imparted high antibacterial activities. However, curcumin gained an advantage over the other two in antioxidant activity and UV protection ability to silk.(2) No evident change of color shade was observed when the dyed silk post-mordanted with aluminum sulfate. After the post-mordanting treatment of Rheum emodi and Gardenia yellow dyed silk with ferrous and ferric salt, the color displayed pale and dull. Color fastness of Rheum emodi and curcumin dyed silk obviously increased after post-mordanting. There was also no obvious change on antioxidant activity after mordanting while UV protection ability increased.(3) Both cationic and crosslinking fixing agents contributed to the improvement of color fastness of silk dyed with curcumin. The antioxidant activity and UV protection ability declined slightly after the treatment of cationic and crosslinking fixing agents, however, the antibacterial activity fell much after treated with crosslinking fixing agent.(4) Reactive UV absorbers was adopted for the modification of curcumin. Modified curcumin had better solubility in water giving rise to the enhancement in the levelness and fastness of dyed silk fabrics. Additionally, good UV protection ability was provided by modified curcumin to silk fabrics in comparation with a decrease of antioxidant activity.