The word vat has come from a vessel. It can be applied in a vat for the coloration of textile products. Vat dyes are natural coloring materials that are solubilized in a vat by the fermentation process called vatting. Vat dyes are insoluble in water but it becomes insoluble form by the vatting process.
Vat dyes
Vat dyes are used in a wide range of water-insoluble dyes, such as blue and anthraquinone derivatives, especially in cellulose fibers. The dye is applied to grow the fiber in a soluble, reduced form, and then the fiber is oxidized back to its invisible form. These dyes are especially fast for light and washing. Bright colors are available in most shades. Originating in medieval Europe, vat dyes are named because the vats used to reduce indigo plants through fermentation are used.
The first artificial vat dyes were invented in 1880 by Adolf von Bear. In 1901, Indanthrene was the first vat dye to be sold commercially. Moreover, these dyes are very resistant to washing and sunlight. These are used in cotton, linen, rayon, and cellulose acetate. Examples of vat dyes include several anthraquinone derivatives such as synthetic alizarin and alizarin yellow, etc.
Properties of vat dyes
i.Vat dyes are water-insoluble dyes.
ii. It has high color fastness, which is uncommon in other dye classes.
iii. It has poor rubbing fastness, but this can be mitigated with special treatments to the fabric.
iv. It is mostly soluble in hot water, and a few are soluble in the presence of little Na2CO3.
v. These dyes' solubility can be improved by adding urea at 50–60 ° C temperature.
vi. It is important for dyeing cotton in pale shades only.
vii. It should be avoided from sunlight because it is sensitive to light, and ester groups are affected to develop prematurely.
viii. All shades are brilliant that are got from vat dyes.
ix. It has less affinity for cellulose, so Na2CO3 is added to enhance dye uptake.
x. Although some dyes show leveling at low temperatures, dyes at higher temperatures encourage the shading level.
xi. These are costly, but the leveling property is excellent.
xii. The tinctorial power of these dyes is too low.
xiii. These dyes are available in two forms powder and paste.
Vat dyes classification
i. Anthraquinone vat dyes
ii. Fused ring polycyclic vat dyes
iii. Indigoid vat dyes
A method of classification divides vat dyes into four policy subgroups: IK, IW, IN, and IN Special, which still leave a few dyes like C.I. Vat Black 9. This classification is based on the different substantivities of the leuco-vat dye anions and dyeing temperature and the need for salt, caustic soda, and hydro concentration to give the best overall dyeing results. The importance of these traditional groups is limited to batch dyeing with leuco-vat anion.
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