Dyeing Properties Of Modified Natural Dyes For Polyamide Fibers

Natural dyes have a long history of application, very good compatibility and bio-degradation to the environment. With the development of economy and culture as well as the gradual establishment of environmental protection, health and green consciousness in people's mind, the attention has been newly paid to natural dyes because their application has benefits to environmental protection, health and so on. At present, natural dyes are commonly applied for the dyeing of silk, wool, cotton and other natural fibers, and their application technology is relatively mature. But their application for the dyeing of nylon, polyester and other synthetic fibers is seldom. Most of natural dyes have many hydroxyl groups, and are not suitable for the dyeing of hydrophobic synthetic fibers due to their nature of strong hydrophilicity. Therefore, it is necessary to carry out the modification of natural dyes, in order to reduce their hydrophilicity, which not only enhances their uptake by synthetic fibers, but also expands their color range and species suitable for the dyeing of synthetic fibers.The emphasis of investigation was given to the discussion of modification methods ass well as the characterization of the chemical structure and nature of modified dyes by their partition coefficient in n-butyl alcohol/water two-phase and by FT-IR and DTA-TG analyses. The special emphasis was focused on the dyeing properties of modified dyes for polyamide fibers compared to those of unmodified dyes. The major results were shown in the following:(1) Saffron yellow was difficult to be hydrolyzed by acid and alkali, whereas Gardenia yellow and red rice pigment were easy to be hydrolyzed under alkaline and acidic conditions, respectively. The result showed C-glycoside was hydrolyzed harder than O-glycoside by acid according to different glycoside atom of natural dyes. Glycoside with ester bond was easy to be hydrolyzed in the alkaline condition.(2) NaOH concentration and temperature in the process of modification had effect on the hydrophobic performance of modified pigment. Modified Gardenia yellow and red rice pigment had small molecular and stronger hydrophobicity. The dyeing properties of modified Gardenia yellow and red rice pigment for polyamide were better than those of unmodified pigment.(3) The dyeing for polyamide fiber with Gardenia yellow and Safflower yellow pigment was mainly due to the existence of an ionic bond between the amino groups in polyamide fiber and negative groups in pigment. The percent of exhaustion increased with an increase in the pH value of dyebath. The pH value caused the change of the conjugated structure and made the pigment be reddish in the acidic conditions.(4) The color fastnesses to washing and rubbing of safflower yellow, gardenia yellow and red rice pigment in polyamide fiber had grade 4 or better. Their fastness of staining to wool, acrylic, nylon, polyester and acetate fiber during washing, had grade 4 or above, but that to cotton was only 2-3. The light fastness of Red rice pigment in polyamide fiber was poor, grade 2 or so, and that in silk basically reached about 3. Dyed silk and polyamide fiber treated with pre-mordant and post-mordant method had better light fastness.