The textile bleaching (or bleaching of textiles) is one of the steps in the

textile manufacturing Textile Manufacturing or Textile Engineering is a major industry. It is largely based on the conversion of fibre into yarn, then yarn into fabric. These are then dyed or printed, fabricated into cloth which is then converted into useful goods ...

process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...

. The objective of bleaching is to remove the natural color for the following steps such as

dyeing Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular c ...

printing Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The ...

or to achieve full

white White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White o ...

. All raw

textile Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not the ...

materials, when they are in natural form, are known as ' greige' material. They have their natural color, odor and impurities that are not suited to clothing materials. Not only the natural impurities will remain in the greige material, but also the add-ons that were made during its cultivation, growth and manufacture in the form of pesticides, fungicides, worm killers, sizes, lubricants, etc. The removal of these natural coloring matters and add-ons during the previous state of manufacturing is called scouring and bleaching. A continuous bleaching range is a set of machines to carry out bleaching action. It consists of several compartments in which fabric moves from one side to another with the help of guide rollers and is treated with chemicals, heated, rinsed, and squeezed. Continuous bleaching is possible for the fabrics in open-width or rope form.

History

Grassing is one of the oldest methods of bleaching

goods. To bleach linen and

cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor pe ...

-based fabrics, the Grassing method has been used. Linen has long been bleached in Europe with Grassing method. The linens were laid out on the grass for over seven days after boiling with the ''lyes of ashes and rinsing''.

Bleachfield A bleachfield or bleaching green was an open area used for spreading cloth on the ground to be purified and whitened by the action of the sunlight. Bleaching fields were usually found in and around mill towns in Great Britain and were an integral ...

was an open area to spread cloth, it was a field near watercourse used by a bleachery. Bleachfields were common in and around the mill towns during the British Industrial Revolution

Discovery of Chlorine

After discovering

Chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

in the late 18th century, when chemical bleaching came into existence, the chemical bleaching rose above Grassing, as it was quicker and possible in indoors.

Scouring

Scouring is the first process carried out with or without

chemicals A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wit ...

, at room temperature or at suitable higher temperatures with the addition of suitable

wetting agent Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming ...

s, alkali and so on. Scouring removes the impurities such as

wax Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to giv ...

es, pectins and makes the textile material

hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are ...

hy or water absorbent. Scouring is then followed by the bleaching process.

Bleaching

Bleaching is the process of decolorizing the material after it has been scoured. Bleaching textiles can be classified as oxidative bleaching and reductive bleaching which can be carried out with oxidizing and reductive bleaching agents. Bleaching agents attack the chromophores and alter the color absorbing properties of the objects.

Oxidative bleaching

Generally oxidative bleachings are carried out using

sodium hypochlorite Sodium hypochlorite (commonly known in a dilute solution as bleach) is an inorganic chemical compound with the formula NaOCl (or NaClO), comprising a sodium cation () and a hypochlorite anion (or ). It may also be viewed as the sodium s ...

sodium chlorite Sodium chlorite (NaClO2) is a chemical compound used in the manufacturing of paper and as a disinfectant. Use The main application of sodium chlorite is the generation of chlorine dioxide for bleaching and stripping of textiles, pulp, and pa ...

or sulfuric acid. Vegetable fibres,

animal fiber Animal fibers are natural fibers that consist largely of certain proteins. Examples include silk, hair/fur (including wool) and feathers. The animal fibers used most commonly both in the manufacturing world as well as by the hand spinners are ...

s, and mineral fibres are the three major types of natural fibers. Natural fibers such as

ramie Ramie (pronounced: , ; from Malay ) is a flowering plant in the nettle family Urticaceae, native to eastern Asia. It is a herbaceous perennial growing to tall;

, jute,

wool Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool. ...

, and regenerated fibers such as

bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...

are all generally bleached with oxidative methods.

Oxygen bleaching action

It is the

conjugated double bonds In theoretical chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in a molecule, which in general lowers the overall energy of the molecule and increases stability. It is conventionally represented as ...

of the substrate that makes the substrate capable of absorbing visible light. Hence, it looks yellower and need bleaching. When bleaching action carries out with oxygen, it removes the chromophoric sites and makes the cloths whiter. Oxygen is a degrading bleaching agent. Its bleaching action is based on ''destroying the phenolic groups and the carbon–carbon double bonds.''. The major source of chemical bleaching is

Hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

that contains a single bond, (–O–O–). When this breaks down it gives rise to very reactive oxygen specie, which is the active agent of the bleach. Around sixty percent of the world Hydrogen peroxide is used in chemical bleaching of textiles and wood pulp.

Reductive bleaching

Reductive bleaching is done with sodium hydrosulphite, a powerful reducing agent. Fibres like

polyamide A polyamide is a polymer with repeating units linked by amide bonds. Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are proteins, such as wool and silk. Artificially made polyamides can be made through ...

s, polyacrylics and polyacetates can be bleached using reductive bleaching technology.

Textile whitening

Bleaching of textiles may include an additional application of optical brighteners (OBAs). Optical brightening agents are chemical compounds that absorb

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

in the

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...

and violet region (usually 340-370 nm) of the

electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...

, and re-emit light in the blue region (typically 420-470 nm) by

fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

. After scouring and bleaching, optical brightening agents are applied to make the textile material appear a more brilliant white. These OBAs are available in different tints such as

blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when ...

violet Violet may refer to: Common meanings * Violet (color), a spectral color with wavelengths shorter than blue * One of a list of plants known as violet, particularly: ** ''Viola'' (plant), a genus of flowering plants Places United States * Viol ...

and

red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...

Whiteness

Whiteness in

colorimetry Colorimetry is "the science and technology used to quantify and describe physically the human color perception". It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color ...

is the degree to which a surface is white. The term "whiteness" refers to the degree to which a surface resembles the properties of a perfect reflecting diffuser, i.e. an ideal reflecting surface that neither absorbs nor transmits light, but instead reflects it evenly in all directions.

CIE Whiteness

CIE Whiteness is a formula that measures the degree of whiteness. The CIE Whiteness Index is a measure or methodology developed by the Commission on illumination.

Gallery

File:Splendor Solis - Traité d'Alchimie - Femmes lavant le linge.jpg, Grassing, laying out linens to bleach in sunlight File:Linen Bleach Green (8251136135).jpg, Linen Bleaching/ Grassing File:Bleekveld.jpg, ''Bleekveld in een dorp'' (''Bleachfield in a village''), circa 1650 (

Jan Brueghel the Younger Jan Brueghel (also Bruegel or Breughel) the Younger (, ; ; 13 September 1601 – 1 September 1678) was a Flemish Baroque painter. He was the son of Jan Brueghel the Elder, and grandson of Pieter Bruegel the Elder, both prominent painters who ...

) File:Jan Brueghel (I) and Joos de Momper (II) - Market and washing place in Flanders.jpg, Market and washing place in Flanders File:Bleaching vats for cloth in the piece. Silk industry, South Manchester, Conn., U.S.A (NYPL b11707678-G90F070 026F).tiff, Bleaching vats for cloth in the piece. File:EB1911 Bleaching - Fig. 4. —High Pressure Blow-through Kier.jpg, High Pressure Blow-through Kier File:EB1911 Bleaching - Fig. 5. —Roller Washing Machine.jpg, alt=Bleaching—Roller Washing Machine, Bleaching—The Mather Kier, cross section File:EB1911 Bleaching - Fig. 6.—The Mather Kier, cross section.jpg, Bleaching—The Mather Kier, cross section File:EB1911 Bleaching - Fig. 7.—The Mather Kier, longitudinal section.jpg, Bleaching—The Mather Kier, longitudinal section File:EB1911 Bleaching - Fig. 8.—Mather & Platt’s Horizontal Drying Machine.jpg, Bleaching—Mather & Platt’s Horizontal Drying Machine File:EB1911 Bleaching - Fig. 9.—Horizontal Drying Machine threaded with Cloth.jpg, Bleaching—Horizontal Drying Machine threaded with Cloth

References

External links

Textile Processing Guide
at thesmarttime.com Textiles Industrial processes Textile techniques {{Industry-stub