Stripping Process of Acid Dyes | Uneven Dyeing of Acid Dyes | Application of Acid Dyes on Silk

Acid dye is water soluble dye. Acid dyes are sodium salts of sullphonic acid but there are a few containing carboxyl group. Its have a direct affinity towards protein fibers and polyamide fibers. So this dyes are frequently applied on protein fibers like wool and silk. Previously I have published article on mechanism of acid dyes. In this article I will give stripping process of acid dyes and application of acid dyes on silk.

Stripping Process of Acid Dyes:
Stripping becomes necessary when uneven dyeing occurs. It is a critical procedure and it is required to match the shade of the dyed fabric with the buyer’s requirement. Stripping process of acid dyes are given below:

a) With the molecularly – dispersed acid dyes, on account of their good migrating properties, continued boiling in the same liquor is often effective. It must, how ever be borne in mind that wool felts if it so boiled form too long.

b) Boiling in fresh liquor with 20% of Glauber‟s salt will strip some of the color, and this can be exhausted again by cautious addition of acid or, preferably, ammonium salt.

c) If treatment with Glauber‟s salt is not successful, more of the color can be stripped by boiling with 0.5% ammonia, or in liquor containing 2% pyridine.

d) Another method is to boil the unevenly-dyed material with 3 to 5% of a cationic, non-ionic mixture such as Tine gal W or Lyogen SMK. When sufficient color has been removed by any of these compounds the wool is rinsed and redeye.

Application of Acid Dyes on Silk
Although silk has an affinity for acid dyes the colors tend to be less fast than on wool. Silk will exert its affinity for acid dyes at lower temperature than is the case with wool, and dyeing is usually commenced at 40ºC and the temperature is not allowed to rise above 85ºC. Glauber‟s salt is not suitable for use with silk as it diminishes its luster. Sulfuric acid damages the silk. Acid used should be acetic acid. While using boiled off liquor the bath must be neutral or only faintly acidic.

Silk dyeing by acid dyes
Fig: Silk dyeing by acid dyes (Image courtesy:
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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