The chemistry of dyeing is highlycomplex, and intricate. There are many steps of production, and each is crucialfor the final colour to emerge with and retain full intensity. A dye is an organic compound, which canbe a natural or synthetic substance, that is used to add or change the colour ofsomething. In the past, mostly all dyes have come from natural sources such asplants and animals.
More recently, chemists have begun to replicate thesecolours found in nature, to synthetic dyes. These synthetic dyes are generally moreintensely coloured, and have better colour fastness. Molecular Structure of a Dye:A dye has 2 main parts. The first one isa chromophore. Each dye has one chromophore. It’s a group of atoms that controlthe colour of the dye and this is their main function.
They hold on tightly totheir electrons. Most dyes also contain 2 auxochromes.These are used to intensify the colour and to form chemical bonds with thefibres, so that the dye particles can attach to the fibre. They give away theirelectrons.
Chromophores and auxochromes are connected by a conjugated system.Types of Dyes:Thereare four main types of dyes. Direct dyes form chemical bonds with fabric. Youimmerse the fabric in a solution and following there is an “uptake” where thedye molecules attach to the fabric molecules. Due to “polar” structure of dyemolecule and fabric molecule, sections of the molecules can have a slightly positiveor negative charge.
The negative part of dye molecule attracts to the positivepart of fabric molecule. There is no sharing of electrons, and there is aweaker bond called “Van Der Waals”, and the color can wash away easily. Anexample of a direct dye, would be tie dye. The second type of dye is adispersed dye.
They are unique in the sense that they are the only insolubledyes, meaning they are not soluable in water. Disperse dyes, are most effectiveat dying polyester. The molecules that make up disperse dyes are the smallestof all the dye molecules.
These dyes are mostly used with dye bath solutions,and to ensure that the process goes smoothly, dispersing products are used tointensify the water soluability of the dye. The third type of dye is a fibrereactive dye. These dyes can react chemically to create covalent bonds. Theseare the strongest dyes. The actual chemical reaction can strip the electrons orprotons from fabrics. This process opens up sites for new bonds, between thedye molecule and the fabric. This reaction produces very strong, covalentbonds. The original fibre-reactive dyeswere created for cellulose fibres, and until today they are mostly used forthat purpose.
Fibre-reactive dyes have been anticipated for a long while, and weren’treally created until 1954. Before that, they tried many times to react the dyeand fibre, but it only resulted in the material being ruined. The fourth type of dye is the vat dyes. In vat dyes,the colour is formed within the fibre. The colour does not appear unless it’sgiven the proper treatments.
An example of a vat dye is indigo. Another examplewould be tyrian purple. This colour doesn’t form until the dye is exposed toair and sunlight.First Synthetic Dye:The first synthetic dye was created by,William Henry Perkins. It was actually discovered by mistake. Perkins wastrying to synthesize quinine, to attempt to find a cure for Malaria, he wasusing coal tars and when he heated it, it became a black gunk and it didn’tabsorb water. He dissolved that in alcohol and discovered the first syntheticdye – purple. This colour is called “mauveine”, or Perkins violet.
He went into mass production funded by hisfamily. He built a factory to synthesize Perkin’s violet and other dyes on alarge scale.Typesof Fabrics used in Dyeing: Silk/wool = proteins, amino acids.Ionic groups, bonding works super wellCotton– cellulose, hydroxyl group, polar Polyethelyne(CH2) not receptive to dyes, Ways to Dye Material:1) Aqueousor conventional dying – most important and most widely used method. Process isuse of dyestuffs. Treatment of textile material in aqueous water solutions2) Solution dyeing– this is part of manufactured fibre production.
It involves adding micro sizedcolored pigments to man made fibre during manufacturing. A Useful Dye Should Include theFollowing:The dye should have an intense colour (how the dye imparts colour totextile materials). Its solubility in water is crucial. This is talking about duringthe process of dyeing, so that water can carry dye particles towards inner molecularstructure of fibre. Another important element is the substantivity to fiber –how the dye molecule will penetrate the inner molecular structure.
The dyes durabilityto wet treatments is another important part. Once the dye is penetrated isinside fibre molecular structure, the kind of chemical bond takes place inbetween fibre and dye molecules is important. Meaning, the colourfastness and propertyof dye, STRONG = record durability to further treatment. Like washing.
Safe,easy to handle, and reasonably priced. Why Dyeing With and Without Mordants Producesa Different Colour: Amordant is basically glue for the dye. It’s a chemical that attaches itself tothe molecular bond, between the dye and the fibre.
Using a mordant is crucialin achieving the desired colour result when dyeing. If a fabric is dyed withouta mordant, the colour will eventually fade with each wash. Soaking the fibre inwater with a mordant, will ensure that the colour stays intense even withwashing.
Without a mordant, the colour will be very dull, and wash out easily.With a mordant, the colour will be intense, and will stay attached to fibreeven after washing.Why Varying Acidity of Dyebaths AffectsFinal Colour: Whereasmost dyes dye better in alkaline baths, acid dyes bond better in acidicdyebaths. Acidic dyes are highly soluable in water, and they donate their H+(hydrogen). The solution is acidic so there are lots of positive charges.
Aciddyes are used to dye certain protein fibres. This includes, feathers, silk andwool. The reason they are called “acid” dyes, is because a very light acid suchas lemon juice or vinegar is added to decrease the pH of the dyebath, making ita little acidic, thereby causing the dye to make bonds with the protein fibres.The varying acidity levels, may affect the final colour. In part 1 of theassignment, the pieces of fabric with lemon juice added came out much lighterthan those without an acid used. Inconclusion, dyeing is a very useful process, and has made many advances inrecent years. The basic process of dyeing is central and it is heavily reliedin our everyday lives, without even realizing it.