Dyeing And Functionalization Of Silk And Cotton Fabrics With Red Natural Dyes

As two typical natural fibers,silk and cotton are widely applied in daily clothing and home textiles,and the former is also used as medical biomaterials.Silk and cotton textiles have frequent contact with the skin when in use,and accordingly require such functions as antibacterial,antioxidant,and UV protection properties.In recent years,the dyeing of textiles with natural dyes has drawn great attention due to its eco-friendliness.In the present work,a series of red natural dyes(lac,cochineal,red rice pigment and hematoxylin)were applied in the simultaneous dyeing and functionalization of silk and cotton fabrics for enhanced antibacterial,antioxidant,and UV protection properties.The present work included the following aspects:(a)the UV-Vis absorption spectral characteristics and thermal stability of anthraquinone and carboxyl group-containing lac and cochineal dyes as well as their interactions with metal ions;(b)the dyeing and functional properties of lac,cochineal,red rice pigment and hematoxylin for silk and cotton fabrics;(c)the influences of post-mordanting by four metallic salts on the colors,color fastness and functionalities of the dyed silk and cotton fabrics.The important results and conclusions were drawn as follows:(a)The UV-Vis absorption spectral characteristics and thermal stability of lac and cochineal as well as their interactions with metal ionsThe colors of lac and cochineal solutions were very sensitive to pH,and their maximum absorption wavelength was shifted toward a long wavelength region(a red-shift effect).Lac and cochineal solutions exhibited good stability in acidic and nearly neutral conditions,whereas they had poor stability in alkaline and high temperature conditions,especially for lac.Metal ions were able to interact with the two dyes,leading to the formation of 1:1 and 1:2(metal ion/dye)complexes for lac and cochineal,respectively.(b)The dyeing and functional properties of lac,cochineal,red rice pigment and hematoxylin for silk and cotton fabricsThe equilibrium adsorption of the four natural dyes on silk conformed to the Langmuir model.Cochineal had the highest affinity to silk,and red rice pigment exhibited the highest adsorption saturation and the best building-up property.The uptake of these dyes by silk greatly depended on the pH of dyebath;the optimum pH for the application of lac,cochineal and red rice pigment was 3,whereas the best result was achieved at pH 6 for the application of hematoxylin.The color change rating for washing of lac,the light fastnes rating of red rice pigment,and the light fastnes rating and color change rating for washing of hematoxylin were low.The anthraquinone-based lac and cochineal exhibited good light fastness.Overall,cochineal had the best color fastness properties.The post-mordanting by aluminium,titanium,ferric and ferrous salts could increase the staining fastness for washing of lac and hematoxylin obviously,and improve the color change fastness for washing of cochineal and red rice pigment.The post-mordanting made the color of the dyed fabrics dull,but the fabrics mordanted with aluminium and titanium salts had higher color brilliance than those mordanted with ferric and ferrous salts.Aluminium potassium sulfate was the best mordanting agent.The lac and hematoxylin dyed fabrics exhibited high antioxidant activity.The hematoxylin and red rice pigment dyed fabrics exhibited high antibacterial activity whereas the lac and cochineal dyed fabrics had poor antibacterial property.The lac and red rice pigment dyed fabrics exhibited good UV protection effect.The post-mordanting obviously the antioxidant activity of the dyed fabrics due to contribution of the phenolic hydroxyl groups to the formation of the dye-metal ion complexes.The post-mordanting exerted complex impacts on the antibacterial and UV protection properties of the dyed fabrics.The post-mordanting by ferric salts could enhance the antibacterial property of the dyed fabrics.(c)The dyeing and functional properties of lac and cochineal for cationized cotton fabricThe equilibrium adsorption of lac and cochineal dyes on cationized cotton conformed to the Langmuir model.The uptake of lac and cochineal dyes by cationized cotton greatly depended on the pH of dyebath,and the color of the lac dyed fabric was more affected by pH than that of the cochineal dyed fabric;the optimum pH for the application of lac and cochineal was 2.2 and 6,respectively.Lac and cochineal showed rapid uptake rate for cationized cotton,and exhibited good building-up on cationized cotton.The cochineal dyed fabric displayed a red color,whereas the lac dyed fabric was orange in color.The cochineal and lac dyed fabrics displayed the dull bluish red and dull red colors,respectively after mordanted with aluminium and titanium salts.The post-mordanting decreased the color brilliance of the dyed fabrics.Whether the post-mordanting was used or not,the lac dyed fabric had poor color fastness.The cochineal dyed fabric exhibited good color fastness,and thereby cochineal was more applicable in the dyeing of cationized cotton fabric for the obtainment of a red color.