Chemistry of dyeing
However the stain does not last for long as it fades off every time that we washes our clothes. A good dye is that which attaches itself to the molecules of the cloth’s fabric can never get out through washing. But what are molecules that are involved in dying? A molecule is a tiny particle that is not easy to see. The diagram below is a model of what a molecule looks like. Each of the above balls represents an atom. Dyes possess color because of the following reasons. They are male to absorb light in the spectrums of between 400-700 mm. They have at least one color-bearing group (chromosphere). There structures are made up of alternating single and double bonds.
This is also referred to as a conjugated system. To understand a mordant better, it can be imagined as molecular glue. Dye and fibers all have a weak affinity for each other. In case a fiber is dyed without a mordant, it will be easily washed hence fading away and even the color will be very dull because of weak attraction (Wanyama et al. A mordant has characteristics of compatibility to both the dye and the fiber. It sticks well to the fiber and also to the dye hence creating attraction between the two. The agents of fading are perspiration, washing and light among other things (Vankar, 2010). When washed, the color changes very fast. This is because of instability of the bonds that exists between the dye and the fabric.
Wash fastness of a dye is greatly influenced by the state of the dyes that are found inside the dye and the diffusion rate. This is because molecules have tendency to increase in size with fastness in washing. The attraction is enabled by various bonds that are formed between these the fiber and the dye. These forces are Van-der Waals bonds, hydrogen bonds and dipolar ponds. Covalent bonds between fibers and dyes are greatly influenced by alkaline conditions. It means that these bonds are well formed when there is little acid. Presence of acids when these bonds are formed can be dangerous since it can reverse the whole process. Therefore chlorine also results in acidic conditions that will finally affect the color (শনিবার, 2018) pH has got a great influence on reactive dyeing.
Care needs to be taken at every stage. At the beginning, the dye bath should be adjusted from neutral conditions to slightly acidic pH conditions. This is to avoid hydrolysis. In case dyeing is not even, conditions can be changed to acidity so that all the yarn is dyed. The strength of this bond is controlled by time of dyeing and temperature at which it is done. Besides chemical dyes, there are also natural dyes. Their use has been reduced by introduction of synthetic dyes. They are derived from inorganic materials hence also called inorganic dyes. Synthetic dyes are cheaper, reliable and ready for use. , El Ghissassi, F. , Bouvard, V. Cogliano, V. Carcinogenicity of some aromatic amines, organic dyes, and related exposures.
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