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Dyeing of Silk with Reactive Dyestuffs:
Because of a circumstance that chemical structures originally developed for acid dyestuff are often diverted as chromophore in reactive dyestuff, there are many reactive dye products that display a high degree of exhaustion on silk under acidic dyeing conditions. However, when using reactive dyestuff, setting of appropriate dyeing conditions for silk is necessary as it is important to ensure fast fixation through a chemical reaction with the fiber. The reaction that takes place between reactive dyestuff and silk fiber is similar to that of hydroxyl groups in cellulosic fiber and is believed to be a chemical bonding of the dyestuff's reactive groups with the hydroxyl groups of oxyamino acid, such as tyrosine and serine, contained in silk protein. In contrast to this, the reactive dyeing of wool, while being another kind of animal fiber, will require different conditions as the reaction is different in that it is with the amino terminal group of wool protein. The following is an example of a silk dyeing recipe using Sumifix Supra dyes.
The most important point to remember is that the reactive dyeing of silk involves alkaline treatment and is therefore prone to problems such as hardening of fabric hand and the generation of friction marks. As the enquiry here concerns yarn dyeing, the generation of friction marks is less likely, however, it should be noted that the reserved use of alkali, as little as 3g/L in the recipe above, is still preferred. The dyeing temperature is set to 75°C on the premise that as little as 3g/L of soda ash is used. While 60°C is the temperature required for the case of using as much as 10g/L, dyeing at 75°C with less alkali is recommended in respect to the resultant fabric hand. The following are examples of dyestuffs that exhibit good applicability to silk in terms of dyeability and fastness. Sumifix Supra Br.Yellow 3GF 150% gran.
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