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Natural Dyes and Pigments of Vegetable Origin

Natural dyes seem interesting since pigments and dyes are useful substances in many applications: from food to textiles, through cosmetics and coating. Some molecules involved in production, formulation or used as dyes are nonetheless pinned by the European REACh regulation. Pigments and dyes are organic or inorganic dyestuffs, natural or synthetic, used to bring a specific color to a medium or a surface.

Pigment and Dyes

The dyes are soluble in the medium of use and have a low or even opacifying power. They are fixed by a chemical bond on the support either directly or with a pretreatment (an example of textile dyeing). Pigments are insoluble materials, ground and dispersed in a medium often used as a binder. They are deposited on the surface of the support to be treated (eg paint) or distributed homogeneously in the mass of the material to be colored (eg plastics).
Unlike dyes, the pigments act on certain properties of use of the final compound by their optical properties (gloss, dullness, opacity …) and physicochemical properties (anticorrosion, incombustibility, consistency …).
In textiles or cosmetics, intermediates are often needed to fix the color. In this way, we speak of mordants in the textile: these products make it possible to graft the coloring substance onto the fiber. In cosmetics, temporary stains require the use of vehicles to fix dyes on the hair.

Pigment adn Dyes  Applications

Dyes are found in food, chemistry, cosmetics, plastics, textiles, and leather. The pigments find their application in cosmetics, paint, inks, coatings, plastics, glassware, ceramics, concrete, etc.

The corresponding market

The global market for organic dyes and pigments was estimated in 2008 at 1.9 million tons and 13.4 billion US dollars.
The average price of a pigment or organic dye can thus be estimated at the US $ 7 / kg. The main producers worldwide are Clariant, BASF, and DIC (Dainippon Ink and Chemicals).

REACh Regulation

Under the REACh regulation, 6 substances are currently subject to authorization (Annex XIV), their production is prohibited, unless authorized by ECHA (as of 17 February 2011).

4,4′-Diaminodiphenylmethane (MDA, a carcinogen) used as an azo dye is one of these (for the production of yellows, reds, oranges or browns). 13 substances used in the manufacture of dyes or pigments are also included in the list of candidate substances for authorization (46 substances in total as at 15 December 2010).

Substance Use (s)
anthracene Formulation of dyes
Lead chromate (yellow) Pigment manufacturing and
colorants
Sulfochromate yellow
lead (CI Pigment Yellow 34)
Dyes and paint
Chromate red, molybdate
and lead sulfate (CI
Pigment Red 104)
Potassium chromate (yellow) Ceramic dye, Manufacturing
pigments / inks,
Mordant for the textile
Amonium dichromate Mordant agent for textiles
Potassium dichromate
Sodium dichromate
Cobalt Sulphate (II) (red) Pigment manufacturing
Cobalt (II) carbonate (purple)
Cobalt Diacetate (II) (red)
Chromium trioxide (red)
Acids generated from
chromium trioxide and its
oligomers

Natural Dyes and Pigments

The pigments and dyes of vegetable origin are organic and extracted from leaves, roots or barks of dyeing plants.
The corresponding chemical families are flavonoids, indigoids, carotenoids, tannins, betanidine, chlorophylls, naphtha-, benzo- and anthraquinones, etc.
There are many more plant dyes than pigments of plant origin. The best known are used for dyeing, food, pharmacy or cosmetics.
Some examples of plant for natural dyes
– Yellow-orange saffron, Yellow Gaude
– Beetroot red, Bright red of madder
– Green of chlorophyll
– Logwood black
– Red, orange, yellow-pink hues of carotenoids
– Tea, chamomile, henna, onions
Natural dyes are recognized for their aesthetic quality. This is due to their composition: the plant extracts indeed contain several substances (from 5 to 25 different molecules), which gives rise to a better rendering.
One technique also involves grafting plant dyes onto a mineral support in order to provide opacification properties: these are called lacquers.
Some examples of plant pigments
– Indigo Blue (Indigo), Pastel Blue (Guede)
– Carbon black (carbonization of vegĂ©taux)
– Garance lacquer (red)

The Brakes on Natural Dyes use

Their small use on an industrial scale is explained by:
– less stability over time (low light fastness, temperature, and solvents),
– their lack of opacity and grip on the supports,
– their cost of production,
– a more difficult estimate concerning the availability of raw materials.
In view of their specific characteristics, it is, therefore, appropriate to attribute appropriate uses (for consumer goods with little exposure to light, for example).

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