Colorants
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The overall landscape of colorants is diverse, and many are not directly derived from hydrocarbons. Also, colorants are small molecules (i.e. not polymers). Colorants used in various industries, including paints, plastics, textiles, and inks, can be derived from a variety of sources.
Here we focus on types of colorants that could be made via the decentralised Unfactory method using synthetic hydrocarbons mostly.
Colorants can be divided to dyes and pigments. The major difference is particle size which in dyes is much smaller. The smaller size means that they are not stable towards ultraviolet radiation – colors fade in sunlight. Pigments typically last. Other differences are that dyes are soluble in many liquids; often in water, they are organic compounds and are absorbed into the material they are applied to. Pigments are often inorganic involving toxic metals and need a binder to help to glue them to the surface of the applied material.
A great majority (two thirds to 80%) of dyes are used for colouring textiles and the second biggest use is colouring paper, the rest going for plastics and leather. For pigments majority goes to paints, followed by plastics and printing inks.
For more: https://www.duraamen.com/blog/differences-between-dyes-and-pigments/
The human eye can see 7 million different colors and the Color Index International – a reference database on colors – lists 11,570 Color Index Generic Names with over 34,500 dyes and pigments.
When searching for local manufacturing methods for colorants using flow chemistry, it’s good to remember that all other colors can be created by mixing the tree primary colors - red, blue and yellow. Hence the problem of local production is much simpler than would appear
As mentioned in this part we focus on organic colorants as they do not need any minerals or just limited amounts to make. Other decentralised approach would be to also include colorants derived from natural sources like plants or insects (e.g., cochineal for red colour).
Based on structure dyes can be divided into azo dyes, anthraquinone dyes, phthalocyanine dyes, other aromatic dyes (azo dyes are the largest group of aromatic dyes) and nitro dyes.
Common organic pigments are azo pigments, lake pigments, phthalocyanine pigments and quinacridone pigments.
Azo dyes have the biggest production volumes in dyes today. They enable large number of structural variations leading to different colors and properties and have vivid colors, especially reds, oranges, and yellows. Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl (aryls are derived from aromatic ring, most commonly from benzene). They are used widely to treat textiles, leather articles, and some foods.
Chemically related to azo dyes are azo pigments, which are insoluble in water and other solvents. Azo pigments lack chemical groups that make them soluble. This makes them difficult to purify at the end of manufacturing process, requiring highly purified precursors (ingredients). Azo pigments are used in plastics, rubber and normal and artist’s paints. They have excellent colouring properties, mainly in the yellow to red range.
Phthalocyanines are limited to blue, cyan and green colors. However, with chemical engineering it is possible to create infrared-absorbing phthalocyanines used for hi-tech applications, like photodynamic therapy (skin cancer medicine that become effective when the right kind of light hits it), optical data storage and solar screens.
for more on industrial applications of phthalocyanines: https://www.worldscientific.com/doi/abs/10.1002/%28SICI%291099-1409%28200006/07%294%3A4%3C432%3A%3AAID-JPP254%3E3.0.CO%3B2-N
Nitro dyes are invariably yellow or orange. Nitro dyes (for example, picric acid) were among the first industrial dyes. They lost their practical importance to better alternatives because light or aging easily causes them to change colour.
Anthraquinone is an aromatic organic compound with formula C14H8O2. Anthraquinone itself is colourless, but red to blue dyes are obtained by introducing electron donor groups such as hydroxy or certain amino groups. Anthraquinone dyes are characterised by very good light fastness.
Also, food is often coloured today. Both natural and synthetic dyes are used. Natural dyes have been used for centuries to colour food, most common being carotenoids, chlorophyll, anthocyanin, and turmeric.
The general principle is not to allow colouring fresh food. A synthetic dye is only allowed after thorough toxicological studies. For example, the U.S. Food and Drug Administration has granted approval to just seven synthetic food colourings for widespread use in food. Reasons for using synthetic colors would be cost, longer shelf life and wider set of colour choices. For decentralised production where you take fresh from nearby growing facilities what you need that day, the need for food colouring seems unnecessary.
Artificial food colorings were originally manufactured from coal tar. Early critics of artificial food colourings were quick to point this out. Today, most synthetic food dyes are derived from petroleum or crude oil.
Paints
Paint is a composition of many components. As described above colour is provided by pigment that is either organic or inorganic. Organic pigments usually are made from oil and inorganic are some form of metal compounds.
Paints also have binder that keeps the pigment in place when the paint dries. Many oil-based binders are used such as alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene (VAE), polyurethanes, polyesters, melamine resins, epoxy etc. Binders may be thick and need a thinner. This can be for example toluene or water.
Fillers are pigments that serve to thicken the film, support its structure and increase the volume. Fillers are usually cheap and inert materials, such as diatomaceous earth, talc, lime, barytes, clay, etc. They are used to make manufacturing the paint cheaper.
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