FORENSIC SCIENCE PAPER No. 5: Forensic Chemistry & Explosives MODULE No. 25: Dyes
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FORENSIC SCIENCE PAPER No. 5: Forensic Chemistry & Explosives MODULE No. 25: Dyes
Weblinks
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https://uqu.edu.sa/files2/tiny_mce/plugins /4300270/al./industrial%20dyes.pdf
http://www.spectroline.com/content/powerful-multiple-led-broad-beam-blue-light- led-lamp-ideal-forensic-inspection-0
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Suggested Readings
Abrahart EN (1977). Dyes and their Intermediates. New York: Chemical Publishing.
Allen RLM (1971). Colour Chemistry. London: Thomas Nelson and Sons Ltd.
FORENSIC SCIENCE PAPER No. 5: Forensic Chemistry & Explosives MODULE No. 25: Dyes
Supramolecular Dye Chemistry by Frank Wurthner, Publisher: Springer (2005)
Did You Know?
The English chemist William Perkins accidentally discovered the synthetic dye, mauve, in 1856, while he was trying to synthesize quinine in aniline.
Dyes are natural or synthetic substance used to add a colour to or change the colour of something.
A dye is a molecule that is soluble in any solvent and absorbs light at visible wavelengths while a pigment is colouring matter that can be dissolved in water or oil to make paint.
Dyes are commercially used in Plastic Industry, Food Industry, Textile Industry and others.
Glossary
Aniline- Represented by the chemical formula of C6H7N. Is also known as aniline oil, Aniline is a very commonly used term in the synthesis of dyes. In fact the term 'aniline dye' is used as a sort of synonym for synthetic dyes.
Affinity - It is referred to as the attraction between two things. While in dyeing affinity it means the preferential attraction of dye towards fiber rather than for solution of the dye bath. A dye that has strong affinity easily leaves the dye solution of dispersion and attaches itself to the fiber being dyed.
Acid Dye- They are a large and popular class of dyes which are applied to polyamide fibers from acidic solutions. Essentially synthetic dyes, they are used for silk, wool and nylon.
FORENSIC SCIENCE PAPER No. 5: Forensic Chemistry & Explosives MODULE No. 25: Dyes
Azo- Azo refers to a chemical compound that contains double nitrogen atoms with a double bond between them (-N=N-). With more than 2000 organic compounds, azo dyes forms the largest group of dyes. They display light-fastness, stability, strongness and respond well to mixing.
"Azo" is the term applied for a class of dyes based on the above chemical structure. Azo dyes may be found among the dye classes of direct, acid, basic, reactive and disperse.
Basic Dye- Basic dyes are the dyes that is able to react with acidic groups on fibers.
They are also referred to as cationic dyes.
Bifunctional Reactive Dye- These are the groups of reactive dyes that typically has more than one type of reactive group in their molecule structure. They are special in the way that these reactive dyes are designed for having the potential to react with the fiber in more than a single way.
Binder- Typically a material, that is nearly colorless, used to attach a pigment to fabric binders are like "glue" that holds the pigment in place. Examples are of Paints that has pigments mixed with binders.
Cation- It is a positively charged ion. Numerous chemicals applied in textile processing are referred to as cationic. That means when the compound ionizes in a solution, it's actually the positively charged ion that is "operational".
Cellulose- A polymer consisting of a large numbers of units, each of the general formula represented by C6H10O5.
Chromophore- It is a colour-bearing compound, by their special property found in an organic molecule they make it appear coloured.
Colour Index- A publication jointly brought out by the Society of Dyers and Colourists of Great Britain and the American Association of Textile Chemists and Colourists.
Chrome- Any of some salts of chromium that is used in tanning and dyeing.
Direct application- A method usually used to describe a process where a solution of dye is locally applied to different areas of fabric, like squirting, painting, spraying, stamping, etc.
Direct Dye- These are a class of dye based on application method which is essentially carried out by immersing the fiber in a dye solution without any requirement of other chemicals for bonding the dye to the fibers.
FORENSIC SCIENCE PAPER No. 5: Forensic Chemistry & Explosives MODULE No. 25: Dyes
Disperse Dye- A dye that is seldom soluble in water. Disperse dyes are found in the dye bath as a kind of suspension or dispersion of microscopic particles, with only a minuscule amount in true solution at any given moment of time.
Exhaust Dyeing- Exhaust dyeing is used for denoting the application of a dye bath of a moderately larger liquor to goods ratio, where the fiber is immersed for a while. It allows the dye molecules to exit the bath and get attach to the fibers.
Enzyme- A type of protein that performs the role of a catalyst in a biochemical reaction.
Enzymes are now popularly used in textile processing. Examples are Amylase enzymes are applied for desizing, and cellulase enzymes are used in modification of cellulosic fabrics.
Fixation- Fixation refers to the formation of a sort of final bond between the fiber and dye. The bond type formed changes with the type of dye and the fiber. To cite an examples, reactive dyes generally fixes by covalent bond, while in the case of acid dyes fixing is done by a variety of mechanisms like hydrophobic forces and ionic bonding.
FBA- Fluorescent brightening agent.
Gel Dyeing- A continuous type of tow-dyeing method where soluble dyes are used to wet-spun fibers in the gel state (i.e. after the processes of extrusion and coagulation, but before drying and drawing).
Hardness- Term used in respect of water, a measure that ascertains the content of minerals that imparts specific properties.
Illuminating Dye- A dye that is mixed with discharge paste in printing methods also referred to as head dyes.
Indigo- Indigo is a sort of natural or synthetic vat dye given the designation of Colour Index Vat Blue . Indigo is perhaps one of the oldest colorants that is used for textiles.
Originally extraction was done from plants, but now it is usually synthetic.
Jet Dyeing- Used to dye Polyester.
FORENSIC SCIENCE PAPER No. 5: Forensic Chemistry & Explosives MODULE No. 25: Dyes
Kilogram- An unit of mass (weight) in the system of metric. It equals approximately 2.2 pounds avoirdupois.
Liquor ratio (also liquor to goods ratio)- The ratio that is used to denote the weight of the dye bath or any other processing bath to the weight of goods that is being dyed or processed.
Leveling Acid Dye- A class of acid dyes, leveling acid dyes offers bright colors and level very easily.
Lightfastness- Light Fastness is typically used as measure to ascertain how resistant a coloring material, such as dye would be fading when exposed to light.
There are a number of standard textile industry methods that evaluates how lightfast a dyed fabric is.
Lake- Lakes are the type of pigments produced as a result of absorbtion of the dye on the substrate. Most common substrate can be alumina hydrate.
Metal-Complex Dye- A dye that typically has co-ordinated metal atoms in its molecule.
A very vital point here to note is that unless the term "metal-complex dye" is applied in direct association with a specific application class of dye, for example "metal-complex reactive dye" or "metal-complex disperse dye" its use can be deprecated.
Mordant- Refers to chemicals that helps in attachment of dyestuff to fibers by bonding to the fiber as well as to the dye. A mordant must show high affinity for both dye and fiber, performing its role to attach the dyestuff to the fiber.
Non-ionic - A chemical that does not ionize in a solution, while remaining is in intact molecular form some surfactants are non-ionic.
No-wick HF- Use lies with Liquid Decorator Colors, for enabling fine line drawing.
Pigment- A substance used in the particulate form that is substantially insoluble in a medium. But pigments can be mechanically dispersed in that medium to carry out modification in its colour and/or properties of light-scattering.
pH- A perfect measure of the concentration of hydronium that is found in a solution.
Reactive Dye- A dye that, under proper conditions, can react chemically with a substrate for forming a covalent dye-substrate linkage.
FORENSIC SCIENCE PAPER No. 5: Forensic Chemistry & Explosives MODULE No. 25: Dyes
Retayne- A type of cationic dye fixing agent. Typically used on cotton fabrics for improving wet fastness of the direct dyes and to add color paper pulp.
Sulphur Dye- A dye, that contains sulphur as an integral part of the chromophore and as well as in attached polysulphide chains. Sulphur dyes are not soluble in water, and must get converted to a soluble form before application.
Sublimation- The conversion of solid directly into gas, without passing through the liquid phase. Some disperse dyes can sublime.
Sodium Hydroxide- Represented by the chemical formula of NaOH; it is a strong base;
also called caustic soda or lye, or just "caustic" in dyeing terms.
Tannic Acid- A mixture of compounds derived from natural sources like oak. Tannic acid treatment, followed by a treatment of tartar emetic, has been reported to improve the washfastness of dyed nylon or wool.
Union Dye- A dye that is generally a mixture of two or more different classes of dye, used to dye blends of fibers.
Ultraviolet- Light that is beyond the portion that is visible of the light spectrum at the blue end. It is the Ultraviolet light that causes fading of colors, and makes fluorescent compounds glow.
Vinyl Sulphone- A type of reactive dye, that is typically used for cellulosic fibers but with some use for wool also. Vinyl sulphone reactive dyes are generally intermediate in their reactivity, so they are used above room temperature, but considerably below the boiling point of water.
Vat Dye- Vat dyes are water-insoluble dye that usually contains keto groups, which is normally applied to the fiber from an aqueous alkaline solution of the reduced enol (leuco) form that subsequently gets oxidised in the fiber to an insoluble form.
Washfastness- Washfastness is used to measure resistance of a dye to washing out.
Wetting Agent- A type of chemical which helps the water to penetrate a material or to form a film over its surface; usually it is a surfactant. Wetting agents are generally used in the dyeing process where it helps the dye solution to penetrate to the individual fibers.
Yarn Dyeing- In this process, Yarn gets dyed before being woven into fabric.
Zinc Formaldehyde Sulphoxylate- A Colour Index Reducing Agent 6, used for application in discharge.
