There are two main sorts of colorants pigments and dyes. Dyes are either soluble within the dyeing medium (e. g. water) or can dissolve into the textile substrate. Pigments are neither soluble within the dyeing medium nor can dissolve into the substrate. Both pigments and dyes are often natural or synthetic. Colorants from natural sources like plants are obtained since pre-historic times. The primary synthetic dye was accidentally discovered by an English chemist named Henry Perkin in 1856.
From the appliance point of view, dyes are classified into different groups, each group being suitable surely sorts of textile substrates. Some commonly used dyes and their suitability for various fibers. For instance, the foremost commonly used sort of dye for cotton. Polyester and acrylic are reactive dyes, disperse dyes, and basic dyes, respectively.
The acid dyes are usually applied under acidic conditions. they’re commonly used for dyeing protein fibers (e. g. wool and silk) and nylon fibers. Acid dyes are anionic in nature. And their charged anions are attracted by charged amino groups in wool under acidic conditions. The appliance of acid dyes on wool or nylon leads to electrovalent bonds or salt links between the anionic dye and therefore the charged groups. Within the fiber under acidic conditions. Additionally to ionic bonds as well as hydrogen bonds also as Van der Waal’s forces can also be formed between the fiber polymer system and therefore the dye molecules.
Because of the high dye-fiber affinity thanks to opposite charges, there’s a risk of rushing of dye molecules towards the fibers at a high rate with the possibility of unlevel dyeing. To avoid unlevel dyeing, some retardation within the dyeing rate is obtained by making use of sodium sulfate.
The acid dyes are further classified into three main groups:
- Leveling dyes
- Super-milling dyes
The main differences within the above three sorts of dyes include their relative molecular mass, an affinity for fiber, leveling properties, amount of leveling agent required, dyeing pH, and fastness properties. Leveling dyes have rock bottom affinity and therefore as well as the best leveling properties but poor wash fastness. Super-milling dyes have the very best affinity, the worst leveling properties but good wash fastness. The leveling properties of dyes are often improved with careful control of dyeing parameters.
The azoic dyes are named so due to the presence of azo radical in their molecule. they’re also referred to as naphthol dyes. Azoic dyes could also be used for dyeing cellulosic materials as well as a few man-made fibers. However, these dyes aren’t popular lately thanks to difficulties in their application and shade matching.
Basic Dyes – Pigments and Dyes
The basic dyes are most ordinarily used for dyeing polyacrylonitrile or acrylic materials. They’re also referred to as cationic dyes due to the presence of charge. Within the dye molecules under dyeing conditions. During dye application, the charged acrylic attracts the charged dye cations for ionic bonding. Thanks to the high attraction between the oppositely charged fiber and dye molecules. There’s a risk of unlevel dyeing due to a high rate of dyeing. This risk could also be reduced by careful control of dyeing temperature and the use of suitable retarding agents.
The basic dyes are documented for his or her intense hues and brilliant shades. Uni-valued by the other class of dyes. Basic dyes have excellent lightfastness due to their resistance as well as to the destructive effect of ultraviolet radiation in sunlight. Their washing fastness is additionally quite good, which can be attributed. To the hydrophobic nature of the acrylic and good substantivity of the dye for the fiber.