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What`s it all about?

  • 27/02/2005

classification of dyesM

Dyes can be classified according to their chemical structure or according to their use. However, classifications vary from agency to agency though there are some fundamental categories that are common to all.

According to the CPCB, there are approximately a million known dyes and dye intermediates out of which about 5,000 are produced commercially. Based on their use-based application, the dyes are divided into 15 groups:

Type of dye Application
Acid dyes Wool, silk, nylon Animal fibres
Azo dyes Cotton Cotton
Basic dyes Acrylic Paper
Direct dyes Cotton, leather, paper Cotton-wool or cotton-silk
Delhi & synthetics combinations
Disperse dyes Polyester
Food dyes Food, cosmetics
Metal complexes Cotton
Mordant dyes Wool
Whitening agent Plastics, paper soap
Pigment dyes Paints & plastics Paints and inks
Reactive dyes Wool & cotton
Solvent dyes Synthetics
Sulphur dyes Cotton & synthetics
Vat dye Cotton & synthetics
Source: 1. Anon 2002, Effluent toxicity status in water polluting industries, Part I – Dye & dye intermediate, bulk drugs and textile industries, Central Pollution Control Board, Ministry of Environment and Forests, Government of India, p 7.
2. Pollution prevention and abatement handbook, World Bank, p 298


pigments


“Pigments,” defines the Coloured Pigment Manufacturers Association of the US, “are coloured, black, white or fluorescent particulate organic or inorganic solids which usually are insoluble in, and essentially physically and chemically unaffected by, the vehicle or substrate in which they are incorporated. They alter appearance by selective absorption and/ or by scattering light. Pigments are usually dispersed in vehicles or substrates for application, for instance in inks, paints, plastics or other polymeric materials. Pigments retain a crystal or particulate structure throughout the colouration process.”

Pigments differ from dyes in that they:

Remain insoluble during application

Have no affinity for the fibres

Require binders

Do not react with the fibres

Pigments are usually mixed with a vehicle that hardens upon drying, forming an opaque coating.

Colour Inorganic pigment Organic pigment
Black Carbon black Aniline black
Copper carbonate
Manganese dioxide
Yellow Lead, Zinc and Barium chromates Nickel azo yellow
Cadmium sulphide
Blue/ Violet Ultramarine Phthalocyanin blue
Prussian blue Indanthrone blue
Cobalt blue Carbazol violet
Green Chromium dioxide Phthalocyanin green
Red Red iron oxide Toluidine red
Cadmium selenide Quinacridones
Red lead -
White

 

Zinc oxide
Antimony oxide
Lead carbonate (basic)
Women who use permanent hair dyes have twice the risk of bladder cancer than non-users


unhealthy dyes


Research has revealed the toxic effects of dyes and pigments on people and the environment. Regulators have therefore banned or restricted the use of colourants classified as highly toxic. The eu banned more than 20 different kinds of azo dyes in the mid 1990s. In December 2003, the us Environmental Protection Agency (usepa) listed process-related solid waste, including sludge from producing certain dyes, plus pigments, food, drug, and cosmetic colourants as hazardous waste, for they “may pose unacceptable risks to human health and the environment when improperly disposed in quantities above specific levels”.

In December 2004, the eu banned sale and use of textile dye “Navy blue 018112”. Tests showed it highly toxic for fish: the “level of concentration that can be reached in rivers from the sewage of the dyeing processes is so high as to suspect damage to aquatic organisms”. Dark coloured dyes block sunlight from entering the water, thus inhibiting photosynthesis and killing aquatic flora and fauna. Impact of dyes on human health is also worrying and has led to regulatory action in several countries.

Dye Health effect
Amarnath

Food, drug and cosmetic (FD&C)

Red No 2, E 123 Europe
Angioedema (heart problem), urticaria

(skin disease), bronchoconstriction
Erythrosine

FD&C Red No 3, E 127 Europe
Thyroid tumours, chromosomal damage
Ponceau

FD&C Red No 4, E 124 Europe
Bronchoconstriction

chest heaviness
Citrus Red No 2 Cancer in animals (used for dyeing skin of oranges)
Tartazine

FD&C Yellow No 5, E 102 Europe
Allergies, thyroid tumours, lymphotic

lymphomas, trigger for asthma,
Sunset Yellow

FD&C Yellow No 6
Rhinitis (runny nose), nasal congestion, purpura (bruising), kidney tumours, abdominal pain, vomiting, indigestion
D&C Yellow No 11 Contact dermatitis
Fast green

FD&C Green No 3
Bladder tumours

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