Important Fabric/Yarn Dyeing & Finishing Terms

Posted by Firoz Kabir on Friday, January 10, 2014 0

In Wet Processing Technology where pretreatment, dyeing, printing and finishing areas have some important terms like as hydrolysis, hygroscopic/hydrophobic, Leuco Compound, M:L ratio, mordanting, pantone, PFD, reactivity/substantivity etc.This is my second post about textile dyeing terms. You can see the other terms to Textile Fiber, Yarn, Woven & Knit Fabric Dyeing Terms

Hydrolysis - The decomposition of a chemical by reaction with water. Some chemicals, such as MX dyes, are effectively destroyed by hydrolysis. Others, such as soda ash, are madeuseful because of hydrolysis. Hydrolysis will occur when susceptible compounds are in aqueous solution, but can also occur because of water absorbed from moist air, without the compound ever appearing wet or damp. This is why many dry chemicals must be kept in sealed containers.

Hygroscopic Tendency to absorb water (usually meaning absorbing it from air). Some of the commonly used chemicals in dyeing are hygroscopic. If they are left exposed to moist air, they will absorb water from the air.

Ion - An electrically charged particle resulting from adding or removing electrons to an atom or a group of bonded atoms.

Ionic bond - A chemical bond as a result of electrical attraction between positive and negative ions; also called salt linkage. In ionic bonding, typically an electron is transferred from one atom to another, leaving one with a positive charge and one with a negative charge. These electrical charges produce strong attraction between the differently charged ions

Leuco - refers to vat dyes in the reduced form; in general a prefix meaning white Vat dyes are converted from the insoluble pigment form to the soluble leuco dye form by means of a reducing agent and an alkali, often sodium hydrosulfite and sodium hydroxide.

Level - Uniform in shade over the surface of a piece of dyed fabric or along the length of dyed yarn.

Light Fastness This is a measure of how resistant a coloring material, such as dye, is to fading due to exposure to light.

Liquor ratio (M:L) This is the ratio of the weight of the dyebath or other processing bath to the weight of the goods being dyed or processed.

Loom state - Fabric as it comes from the loom, usually unbleached, containing size, and maybe a bit dirty. Loom state is essentially synonymous with greige or grey.

Mercerization - Treatment of cotton yarn or fabric with a strong solution of sodium hydroxide; named after its inventor, John Mercer. Mercerizing cotton can significantly improve its dye uptake, especially if there are immature fibres present. Typically it is done using about 20% to 25% sodium hydroxide solution at around 20°C

Molecular weight - The weight of a molecule; the sum of all atomic weights of all the atoms in the molecule;

Mordant - a chemical that aids attachment of a dyestuff to fibres by bonding to both the fibre and the dye. A mordant must have high affinity for both the dye and the fibre, acting to attach the dyestuff to the fibre.

Padding - a dyeing method with very low liquor to goods ratio, where typically only enough strong dye solution is used to saturate the fabric. Padding can have the advantage of high dye yield.
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Pantone - A company and its trademark. The Pantone Company produces a wide range of color guides useful in almost any industry dealing with color. The colors in the guide are widely accepted as standards. Colors are sometime seen described as a Pantone number: Pantone applies a unique number to each color.

pH - a measure of the concentration of hydronium (H3O+ , H+ attached to a molecule or water) in a solution. pH = -log[H30+ ] (that is, the negative base-10 logarithm of the concentration of hydronium) . Acids have pHs less than 7; bases have pHs greater than 7. A pH of 7 is neutral. The normal pH range is 0 to 14.

Pigment - A colored substance that is insoluble in water, usually in the form of a fine powder
Pigments are used to color many types of paint, including some textile paints, and almost all “inks” used for screen printing. Pigments need some sort of binder to hold them onto fabric.

Pigment dyeing - coloring fabric with pigments mixed with a binder; this term is considered to be improper, since‘ dyeing’ is generally restricted to application of colorants that are soluble, and pigments are insoluble

Precipitate - A precipitate has low solubility in the solution from which it was formed, giving a cloudy appearance, which sediments at the bottom of the solution.

Prepared For Dyeing (PFD) These are the fabric or garment that is specially made to be dyed; sometimes “preferred for dyeing. PFD fabrics have been desized, scoured, and fully bleached, but have been processed without optical brighteners or softeners which can interfere with dye uptake. This fabrics are processed with cotton fabric as well as made with cotton sewing threads..

Reduction clearing - Removal of unfix dyes on the surface of fabric by use of a reducing agent.
Fine particles of disperse dye often remain on the surface of dyed fabric. These particles can cause wash
fastness problems, yet are hard to fully remove by washing alone. A mixture of about 2 grams per litre each of sodium hydrosulfite and sodium carbonate is used at about 70 degrees Celsius for about 20 minutes. Dye inside the fibre is not affected by this treatment.

Scour (Scouring) - Essentially, thoroughly washing fibers, yarn or fabric to remove contaminants such as oil, wax or any other impurities. Yarns and fabrics may be dirty, contain natural waxes or oils, or have been treated with size or lubricants used in spinning, weaving or knitting. Usually Alkali treatment is used to scour the substrates as well as this process is known as scouring.

Singeing - an industrial defibrillation process where rapidly-moving fabric passes over a flame or a very hot plate in order to burn away fibres poking up from the surface. To remove the projecting fiber from the surface of the fabric, passed through gas burner or roller is commonly known as singeing.

Size (Sizing)The ingredient applied to yarns or fabrics to make them stiffer or temporarily bind fibers together. Sizing is used extensively, especially for cellulose fibers, to make them easier to process or protect them from damage during high-speed weaving.

Soaping - With respect to dyeing, the process of washing dyed fabric with very hot (often boiling) water with surfactants, rarely actually soap, to remove dye that is not fixed to the fiber.

Stripping - Removal of dye from fabric. Stripping is usually done with a reducing agent such as thiox, formosul or sodium hydrosulfite and often requires hot to boiling conditions. Some dyes are difficult to strip, and the result often is not white.

Stock solution - A solution of known strength, made up with the intent of dilution or mixing before final use. Stock solutions are a convenient way of avoiding the need to weigh chemicals each time you need to use some. For example, if you need 0.27 grams of Smurf extract in a blue dye formula, and you have a stock solution of 10% extract, you would measure 2.7 milliliters of stock solution to get that amount.

Sublimation - The conversion of a solid directly to a gas, without passing through a liquid phase
Some disperse dyes will sublime. This can make dyed fabric subject to fading due to heating, as from ironing at high temperature.

Substantive (Substantivity) - Tendency of a dye to move from a solution onto fibers in the solution
A dye that is substantive will leave the dye bath and be concentrated on the fiber in the bath. Without
substantivity, most of the dye would simply remain in solution or dispersion in the bath. Dye substantivity is generally associated with the molecular structure of the dye, and often big molecules have high substantivity, while small molecules have low substantivity.

Subtractive - with reference to color, removal of colors from light reflected from a surface
A surface that is illuminated by white light and that reflects all visible colors will appear white.

Tendering - Weakening of a fiber, normally meaning as a result of chemical degradation. Cellulose fibers can be tendered by acids or by excessive action of oxidative bleaches.

Union dye - A dye that is a mixture of two or more different classes of dye, used typically to dye blends of fibers.

Van Der Waals forces Intermolecular forces as a result of localization of electrical charge within molecules. A molecule considered as a whole is electrically neutral. Because of the way in which electrons are held, there may be local areas that appear to have positive or negative electric charge, either permanently or temporarily. These charges lead to attraction between molecules. These forces are weak and easily broken, but they can be important in dyeing. They can be important in affinity, and hold dye molecules on the fiber near to where a much stronger bond may ultimately be formed.

Wash Fastness - A measure of the resistance of a dye to washing out of the fiber, yarn or fabric as well as garments. Wash fastness tests are concerned not only with loss of dye from the
colored fabric, but also transfer of dye from the wash liquor to other items.

Washing soda (sodium carbonate) Washing soda, if “pure”, is usually sodium carbonate decahydrate (Na2CO3.10H20). Retail washing soda (Local Soda) contain additives such as detergents, salt and optical brighteners, and is therefore not a good substitute for soda ash for dyeing

About the Author

Md. Firoz Kabir(M.Sc in Textile Engineering)

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