Major Pollutants

• Aromatic amines

• Heavy metals

• Ammonia

• Alkali salts

• Toxic solids and large amounts of pigments

• Chlorine

Classification of Dyes

• Acid Dye: Water soluble anionic dyes that are applied to fibres such as silk, wool, nylon and modified acrylic fibres from neutral to acid dye baths. Attachment to the fibre is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fibre. Acid dyes are not substantive.

• Basic Dye: Water soluble cationic dyes that are mainly applied to acrylic fibres but find some use for wool and silk.

• Mordant Dye: As the name suggests these dyes require a mordant. This improves the fastness of the dye on the fibre such as water, light and perspiration fastness. The choice of mordant is very important as different mordents can change the final color significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. The most important mordant dyes are the synthetic mordant dyes (chrome dyes) used for wool, these comprise some 30% of dyes used for wool and are especially useful for black and navy shades. The mordant used is potassium dichromate applied as an after-treatment.

• Vat Dye: These dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water soluble alkali metal salt of the dye. In this leuco form these dyes have an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye.

• Reactive Dye: First appeared commercially in 1956, after their invention in 1954 by Rattee and Stephens at the ICI Dyestuffs Division site in Blackley, Manchester, UK. They are used to dye cellulosic fibres. The dyes contain a reactive group, either a haloheterocycle or an activated double bond, that, when applied to a fibre in a weakly alkaline dye bath, forms a chemical bond with a hydroxyl group on the cellulosic fibre.

• Disperse Dye: Originally developed for the dyeing of cellulose acetate. They are substantially water insoluble. The dyes are finely ground in the presence of a dispersing agent then sold as a paste or spray dried and sold as a powder. They can also be used to dye nylon, triacetate, polyester and acrylic fibres. In some cases a dyeing temperature of 130 degree Celcious is required and a pressurized dye bath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding

• Azoic Dye: A dyeing technique in which an insoluble azo dye is produced directly onto or within the fibre. This is achieved by treating a fibre with a diazo component and a coupling component. With suitable adjustment of dye bath conditions the two components react to produce the required insoluble azo dye. This technique of dyeing is unique in that the final color is controlled by the choice of the diazo and coupling components

Textile Manufacturing Process