Question

Write a short note on Disperse dyes.

Answer 1

Hint: To answer this question you must recall the characteristics and properties of dyes especially disperse dyes. Dyes are coloured substances that form chemical bonds to the substrate they are added to and impart them a colour.

Complete answer:
Disperse dyes are a type of synthetic dyes. It is a kind of an organic substance that is free of an ionizing group. They are less soluble in water than other dyes and are thus used to dye synthetic textile materials. Disperse dyes are most commonly used in the dyeing process of the polyester yarn of fabrics.
Disperse dyes are generally available in the form of powders, which are prepared by the milling of press cake with a uniform weight of a suitable auxiliary product along with some amount of water, followed by drying, and then mixing the dried substance with diluents to produce a product containing around 15– 40% of the dye.
The very fine particle size of these dyes provides an increased surface area that helps in dissolution to allow uptake of the dye by the fibre. The dyeing rate significantly depends on the choice of dispersing agent used during the process.

Note:
Disperse dyes generally have a small, planar and non-ionic structure, with polar functional groups like hydroxyl- alkyl group, nitro group and cyanide group attached. The shape of the dye is such that it makes it easier for the dye to slide between the tightly packed polymer chains of the fiber, while the polar groups improve the solubility in water and increase the dipolar bonding between dye and polymer.