Textile Fiber, Yarn, Woven and Knit Fabric Dyeing Terms

Posted by Firoz Kabir on Thursday, January 9, 2014 0

Woven or knit fabric dyeing terms such as affinity, antichlor, shade, bonding, electrolyte, exhaustion, fixation, griege, hardness etc are very important for wet processing technology learning as well as engineering students. Some of them I have been used to describe here.

Affinity – The attraction between two items, in dyeing affinity essentially means the preferential attraction of the dye for the fibre rather than for the solution of the dye-bath. A dye with high affinity readily leaves the dye solution of dispersion to attach to the fiber being dyed.

Anion - A negatively charged ion. Many chemicals used in textile processing are described as anionic. This means that when the chemical ionizes in solution, the ion that is “functional” has a negative electrical charge. Most dyes are anionic. Surfactants, including some used as fabric softeners, may be anionic (others are cationic or non-ionic).

Anhydrous (without water) - Many “dry” chemicals may contain some water as part of the crystal structure. Although this can often be compensated for in making up formulas, it is often more convenient to use chemicals that contain no water, that is, that are anhydrous.

Antichlor – This is a chemical used to neutralize chlorine bleach. It can be very difficult to completely rinse chlorine bleach out of fabric. The residual bleach can interfere with subsequent dyeing as well as it will eventually damage the fiber. A rinse in a solution of antichlor, most commonly sodium bisulfite, will quickly neutralize the bleach. Hydrogen peroxide also functions to neutralize chlorine bleach. On the other hand for neutralization of chlorine in water used to make up dye baths, sodium thiosulfate is the preferred antichlor agent.

Auxochrome – The groups which are associated to dyestuff’s chemical structure refer to the color increasing group.

Batch or Batching - leaving goods saturated with dye solution for some period of time, typically hours, and typically at “room temperature” for the dye to fix to the fibre

Boil – Usually, to heat or maintain a solution at the temperature where the vapor pressure of a liquid equals atmospheric pressure, that is, its boiling point; in dyeing sometime called “atmospheric boil” to distinguish from boiling under pressure.

Bond – Basically three types of bond are there, which are hydrogen bond, ionic bond, covalent bond and another thing is there which is van der Waals forces. From these bonds hydrogen bonds are weakest, ionic bonds intermediate in strength, and covalent bonds are strongest. Van der Waals forces are something of a special case.

Carbonizing – It is the treatment of wool with acid (Sulphuric Acid), followed by partial drying and
heating to remove plant materials.The hot acid will degrade or ‘carbonize’ bits of plant matter in the wool, so that it is easily removed by subsequent mechanical methods.

Cation - A positively charged ion. Many chemicals used in textile processing are described as cationic, meaning that when the compound ionizes in solution, it is the positively charged ion that is “functional”.

Chromophore – It is color-bearing compound, typically meaning the part of a larger organic molecule that makes it appear colored. Dyes typically have a chromophore chemically bonded to other structures that impart desired characteristics such as affinity for the fibre and solubility in water. A particular chromophore structure may be found in a variety of dye classes and in pigments.

Color Index - a joint publication of the Society of Dyers and Colourists in Britain and the American Association of Textile Chemists and Colorists. The Colour Index contains information on dye structures, classifications, manufacturers and processes.

Covalent bond - a chemical bond where a pair of electrons is are shared relatively equally between two atoms in the compound. Covalent bonds are formed between the fibers and reactive dyes. These are the strongest type of chemical bond,and are responsible for the excellent wash fastness of reactive dyes.

Crocking - Transfer of color from dyed or pigmented fabric by rubbing to a cloth name crocking cloth. Wet crocking refers to transfer of color from a piece of dyed fabric to another piece of fabric, or to an undyed area of the same fabric, while the fabric is wet. Dry crocking means the same, except that the fabric is dry.

Density - As a measure of physical properties of a substance, the ratio of the mass (weight) of the substance to its volume.

Depth of shade - Ratio of weight of dye to weight of goods dyed, usually expressed as percentage. Depth of shade (DOS), in these terms, is not really a very good way of comparing the darkness or intensity of color of finished fabrics, due to inherent differences in the hues of different dyes within a family, differences between dye families, and differences due to the nature of the fabric. Dye manufacturers’ shade cards are typically show one or two depths of shade for a particular dye, often between 1% and 4%, except for black, which is typically 3% to 6%.

Desizing - Desizing is an important step prior to dyeing fabric which is done to remove size materil from fabric, since size can interfere with dye uptake. Some size materials wash out easily. Starch is commonly used for size, and can be quite difficult to remove. Amylase enzymes are often used industrially for starch removal. Some sizes can be readily removed by hot water washing.

Dope Dyeing
- Coloration of the polymer prior to manufacture of the fibre.This is really a misnomer, since the colorants are almost always pigments: “mass pigmentation” is a more accurate term. Some synthetic polymers such as polypropylene cannot be dyed after being made into fibres, and coloration by adding pigments to the melted material is the only method available. Pigmenting prior to making fibres can also produce washfastness and lightfastness that is higher than can be obtained with any dyeing process.

Dye Activator - One dye seller’s name for an alkali intended for use with reactive dyes; believed to be pure soda ash. This term is somewhat misleading: in the case of most reactive dyes on cellulose fibers, it is the fiber, not the dye, that is “activated” (an exception to this is vinyl sulfone dyes).

Electrolyte – This is a substance that makes an electrically conductive solution when it is dissolved in water. Electrolytes dissociate to form ions in solution. Fibers immersed in water develop a negative electrical charge at their surface. Most dyes are anionic, so the fiber tends to repel the dye. The presence of electrolytes in the dye bath helps to overcome this repulsion so that the dye can gain access to the surface of the fiber. The most common electrolyte in dyeing is sodium chloride (common salt). Sodium sulfate is used sometimes. The acids used with acid dyes also behave as electrolytes.

Exhaust Dyeing - Generally meaning the use of a dye bath of moderately large liquor to goods ratio, in which the fiber is immersed for some time, allowing the dye molecules to leave the bath and attach to the fibers. Exhaust dyeing is the typical process for most commercial fabric dyeing. It depends of dye substantivity.

Exhaustion – It is the leaving of a dye from the dye bath and attachment to the fibre being dyed. The ideal dye would exhaust totally - all the dye in the dye bath would end up on the fibre. Exhaustion is sometimes specified as a percentage. For example, 60% exhaustion would mean that 60% of the total amount of dye has attached to the fiber, and 40% is still in solution. Reactive dyes generally show moderate exhaustion while many acid dyes exhaust to the point that the dye liquor becomes nearly colorless.

Fixation – It is formation of the “final” bond between the dye and fiber. The bond type formed between the fiber and the dye varies with the type of dye and the fiber. As examples, reactive dyes fix by covalent bonding while acid dyes fix by a variety of mechanisms such as ionic bonding and hydrophobic forces. Disperse and vat dyes are fixed in the fiber largely by physical entrapment of insoluble dye within the fiber.

Fixative - In dyeing, a chemical that helps improve wash fastness of dyed fabric. Some types of dye do not bond strongly to fibers, and will wash out over time. Fixatives applied after dyeing can help, although some will degrade light fastness or cause shade changes.

Formosul – It is a trade name for sodium formaldehyde sulfoxylate.

Fuchsia – This is a bluish-red color named after a flower named after Herr Fuchs.

Glass Transition Temperature - The temperature above which a material changes from a brittle,“glassy” nature to a rubbery nature; on cooling, the material changes back to glassy Synthetic fibres, such as polyester and nylon show this change of physical character. The rate of dye uptake increases dramatically when the fiber is near or above the glass transition temperature. If the glass transition temperature is above the boiling point of water, as it is with polyester, the dyeing rate is extremely slow even at the boil.

Greige – It means the grey stage of fabric or the fabric used to dyeing. In North America, greige is often used to describe loom state fabric that is unbleached, contains size and lubricants, and may be a bit dirty. Greige goods are made ready for dyeing by singeing, desizing, scouring and usually bleaching.

Hand Feel -   the feel of a fabric through hand. Hand of a fabric is quite subjective, and often difficult to describe. Both chemical and mechanical treatments are frequently used to alter the hand of a fabric. To increase hand feel of fabric softener is used usually.

Hardness - With respect to water, a measure of the content of minerals that impart certain properties.
Calcium and magnesium ions are main cause of hardness in  water. They can interfere with some chemical processes in preparation and dyeing.

Hydrogen bond – It is the weakest chemical bond in which hydrogen that is already covalently bonded to one atom is electrically attracted to a lone pair of electrons on another atom. Some atoms such as oxygen are said to be very electronegative, which means that they strongly draw bonding electrons toward themselves. If hydrogen is bonded to such an atom, the hydrogen “appears” to have some positive charge.

About the Author

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

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