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bleach

  (blēch) pronunciation

v., bleached, bleach·ing, bleach·es.

v.tr.
  1. To remove the color from, as by means of chemical agents or sunlight.
  2. To make white or colorless.
v.intr.

To become white or colorless.

n.
  1. A chemical agent used for bleaching.
    1. The act of bleaching.
    2. The degree of bleaching obtained.

[Middle English blechen, from Old English blǣcan.]


 
 
How Products are Made: How is bleach made?

Background

Bleach is a chemical compound derived from natural sources used to whiten fabrics. Bleach works by the process of oxidation, or the alteration of a compound by the introduction of oxygen molecules. A stain is essentially a chemical compound, and the addition of bleach breaks down the molecules into smaller elements so that it separates from the fabric. Detergent and the agitation of the washing machine speed up the cleaning process. The disinfecting properties of bleach work in the same manner—germs are broken down and rendered harmless by the introduction of oxygen. In industry, different forms of bleach are used to whiten materials such as paper and wood, though most bleach is used to launder textiles.

History

Humans have been whitening fabrics for centuries; ancient Egyptians, Greeks, and Romans bleached materials. As early as 300 B.C., soda ash, prepared from burned seaweed, was used to clean and whiten cloth. During the Middle Ages, the Dutch perfected the bleaching of fabrics in a process called crofting, whereby fabrics were spread out in large fields for maximum sunlight exposure. Textile mills as far away as Scotland shipped their material to the Netherlands for this bleaching. The practice quickly spread throughout Europe, and bleaching fields were documented in Great Britain as early as 1322. In 1728 a bleaching company using Dutch methods went into business in Galloway, Scotland. In this process, the fabrics were soaked in a lye solution for several days, then "bucked," or washed clean. The fabrics were then spread out on the grass for weeks at a time. This process was repeated five or six times until the desired whiteness was achieved. Next, the fabric was treated with sour milk or buttermilk, and again bucked and crofted. This method was lengthy and tedious, and it monopolized large tracts of land that could have been used for farming.

Late in the 18th century, scientists discovered a chemical that had the same effect as crofting, but yielded much quicker results. In 1774, Swedish chemist Karl Wilhelm Scheele discovered the chemical element chlorine, a highly irritating, green-yellowish gaseous halogen. In 1785, the French scientist Claude Berthollet found that chlorine was an excellent whitening agent in fabrics. Some mill operators attempted to expose their fabrics to chlorine gas, but the process was so cumbersome and the fumes so strong that these attempts were soon abandoned.

Near Paris, in the town of Javel, Berthollet began a small facility for the manufacture of a new product called "Eau de Javelle." The bleaching powder consisted of potash (soda ash) which had absorbed chlorine gas. In 1799, another bleaching powder was invented by Scottish chemist Charles Tennant. In the early years of the Industrial Revolution, his patented lime powder was widely used to whiten a variety of fabrics and paper products. To make the bleaching powder, slaked lime (lime treated with water) was spread thinly over the concrete or lead floor of a large room. Chlorine gas was pumped into the room to be absorbed by the lime. Though an effective whitener, the powder was chemically unstable. It was commonly used until around World War I, when liquid chlorine and sodium hypochlorite solutions—the forerunners of modern household bleach—were introduced. About this time, researchers found that injecting salt water with electrical current broke down the salt (sodium chloride) molecules and produced a compound called sodium hypochlorite. This discovery enabled the mass production of sodium hypochlorite, or chlorine, bleach.

Types of Bleach

Today, bleach is found in nearly every household. It whitens fabrics and removes stains by a chemical reaction that breaks down the undesired color into smaller particles that can be easily removed by washing. The two types of household bleach are chlorine bleach and peroxide bleach. Peroxide bleach was introduced in the 1950s. Though it helps to remove stains, especially in higher wash temperatures, it will not bleach most colored materials and does not weaken fabrics, as does sodium hypochlorite bleach. Peroxide bleach does not disinfect and is commonly added to laundry detergents which are advertised as color-safe. It also has a longer shelf life than chlorine bleach. Peroxide bleach is more commonly used in Europe, where washing machines are manufactured with inner heating coils that can raise the water temperature to the boiling point.

The more common form of household bleach in the U.S. is chlorine bleach. It is most effective in removing stains and disinfecting fabrics. Chlorine bleach is cheap to manufacture and effective in both warm and hot wash temperatures. However, it has strong chemical properties which can weaken textile fibers.

The disinfecting properties of chlorine bleach can also be useful outside the laundry. Chlorine bleach disinfects drinking water where groundwater contamination has occurred, as it is a powerful germicide. It was first used to sanitize drinking water in New York City's Croton Reservoir in 1895, and is approved by the government for sanitizing equipment in the food industry. In recent years, bleach has been promoted by community health activists as a low-cost method of disinfecting the needles of intravenous drug users.

Raw Materials

The raw materials for making household bleach are chlorine, caustic soda, and water. The chlorine and caustic soda are produced by putting direct current electricity through a sodium chloride salt solution in a process called electrolysis. Sodium chloride, common table salt, comes from either mines or underground wells. The salt is dissolved in hot water to form a salt solution, which is then treated for impurities before it is reacted in the electrolytic cell.

The Manufacturing
Process

The manufacture of sodium hypochlorite bleach requires several steps. All the steps can be carried out at one large manufacturing facility, or the chlorine and caustic soda can be shipped from different plants to the reactor site. Both chlorine and caustic soda are hazardous chemicals and are transported according to strict regulations.

Preparing the components

  • Caustic soda is usually produced and shipped as a concentrated 50% solution. At its destination, this concentrated solution is diluted with water to form a new 25% solution.
  • Heat is created when the water dilutes the strong caustic soda solution. The diluted caustic soda is cooled before it is reacted.

The chemical reaction

  • Chlorine and the caustic soda solution are reacted to form sodium hypochlorite bleach. This reaction can take place in a batch of about 14,000 gallons or in a continuous reactor. To create sodium hypochlorite, liquid or gaseous chlorine is circulated through the caustic soda solution. The reaction of chlorine and caustic soda is essentially instantaneous.

Cooling and purifying

  • The bleach solution is then cooled to help prevent decomposition.
  • Often this cooled bleach is settled or filtered to remove impurities that can discolor the bleach or catalyze its decomposition.

Shipping

  • The finished sodium hypochlorite bleach is shipped to a bottling plant or bottled on-site. Household-strength bleach is typically 5.25% sodium hypochlorite in an aqueous solution.

Quality Control

In the bleach manufacturing facility, the final sodium hypochlorite solution is put through a series of filters to extract any left-over impurities. It is also tested to make certain that it contains exactly 5.25% sodium hypochlorite. Safety is a primary concern at manufacturing plants because of the presence of volatile chlorine gas. When the chlorine is manufactured outside the reactor facility, it travels in liquid form in specially designed railroad tank cars with double walls that will not rupture in the event of a derailment. On arrival at the plant, the liquid chlorine is pumped from the tank cars into holding vat.. As a safety measure, the tank cars have shutoff valves that work in conjunction with a chlorine detection system. In the event of a chlorine leak, the detection system triggers a device on the tank that automatically stops the transmission of the liquid in 30 seconds.

Inside the facility, chlorine vats are housed in an enclosed area called a car barn. This enclosed room is equipped with air "scrubbers" to eliminate any escaped chlorine gas, which is harmful to humans and the environment. The vacuum-like scrubber inhales any chlorine gas from the enclosed area and injects it with caustic soda. This turns it into bleach, which is incorporated into the manufacturing process. Despite these precautions, safety and fire drills are scheduled regularly for plant personnel.

Special Considerations in
Packaging

Household sodium hypochlorite bleach was introduced to Americans in 1909 and sold in steel containers, then in glass bottles. In the early 1960s, the introduction of the plastic jug brought a cheaper, lighter, and nonbreakable packaging alternative. It reduced transportation costs and protected the safety of workers involved in its shipping and handling. Additionally, the thick plastic did not permit ultraviolet light to reach the bleach, which improved its chemical stability and effectiveness. In recent years, how-ever, plastic containers have become an environmental concern because of the time it takes the material to decompose in a landfill. Many companies that depend on plastic packaging, including bleach manufacturers, have begun to reduce the amount of plastic in their packaging or to use recycled plastics. In the early 1990s, Clorox introduced post-consumer resins (PCR) in its packaging. The newer bottles are a blend of virgin high-density polyethylene (HDPE) and 25% recycled plastic, primarily from clear milk jug-type bottles.

Consumer Safety

The bleach manufacturing industry came under fire during the 1970s when the public became concerned about the effects of household chemicals on personal health. Dioxin, a carcinogenic byproduct of chemical manufacturing, is often found in industrial products used to bleach paper and wood. In its final bottled form, common sodium hypochlorite bleach does not contain dioxins because chlorine must be in a gaseous state for dioxins to exist. However, chlorine gas can form when bleach comes into contact with acid, an ingredient in some toilet-bowl cleaners, and the labels on household bleach contain specific warnings against such combination.

In addition to the danger of dioxins, consumers have also been concerned about the toxicity of chlorine in sodium hypochlorite bleach. However, the laundry process deactivates the potentially toxic chlorine and causes the formation of salt water. After the rinse water enters the water system through the household drain, municipal water filtration plants remove the remaining traces of chlorine.

Where To Learn More

Periodicals

Ainsworth, Susan. "Resurgence in Demand Reviving Market for Sodium Chlorite." Chemical & Engineering News, March 22, 1993, pp. 11-12.

Grime, Keith and Allen Clauss. "Laundry Bleaches and Activators." Chemistry and Industry, October 15, 1990, pp. 647-49.

[Article by: Carol Brennan]

The manufacturing section of this entry was written with the help of Clorox Company.


 
Thesaurus: bleach

verb

    To lose normal coloration; turn pale: blanch, etiolate, pale, wan. See colors/colorless.

 
Antonyms: bleach

v

Definition: whiten
Antonyms: blacken, darken, yellow

 
Britannica Concise Encyclopedia: bleach

Solid or liquid chemical compound used to whiten or remove the natural colour of fibres, yarns, paper, and textile fabrics. Sunlight was the chief bleaching agent up to the discovery of chlorine in 1774 by Karl Wilhelm Scheele (b. 1742 — d. 1786) and the demonstration of its bleaching properties in 1785 by Claude-Louis Berthollet (b. 1748 — d. 1822). In textile finishing, the bleaching process is used to produce white cloth, to prepare fabrics for other finishes, or to remove discoloration. Chlorine, sodium hypochlorite, calcium hypochlorite, and hydrogen peroxide are commonly used as bleaches.

For more information on bleach, visit Britannica.com.

 
Columbia Encyclopedia: bleaching,
process of whitening by chemicals or by exposure to sun and air, commonly applied to textiles, paper pulp, wheat flour, petroleum products, oils and fats, straw, hair, feathers, and wood. Chemical methods include oxidation, as by hypochlorites, ozone, and the per-compounds; reduction, as with sulfur dioxide; and adsorption, as by bone charcoal used to decolorize sugar solutions. Textiles have long been whitened by grass bleaching, a method virtually monopolized by the Dutch from the time of the Crusades to the 18th cent. They developed a technique in which goods were alternately soaked in alkaline solutions and grassed, or crofted, a procedure in which they are exposed to air and sunlight; the goods were then treated with sour milk to remove excess alkali. Later they substituted dilute sulfuric acid for the milk. In 1785 the French chemist Claude Berthollet suggested the commercial application of chlorine for bleaching, and in 1799 the Scottish chemist Charles Macintosh invented bleaching powder, or chloride of lime, the first of the modern chemical bleaches. Bleaching processes vary for different fibers. Cotton, naturally a grayish yellow, contains waxy and oily impurities that interfere with the action of dyes. It must be scoured and boiled in huge kettles (kiers) before bleaching. Grass bleaching has been combined with or superseded by chemical methods, which are deleterious unless rigidly controlled. Four degrees, ranging from quarter to full bleach, are recognized in the industry. Full bleach is reputed to weaken the fiber as much as 20%. Since chlorine bleaches react with the protein of animal fibers, silk and wool are commonly bleached with hydrogen peroxide. Although sulfurous acid or sulfur dioxide are also used for wool, they do not permanently whiten it. For effective bleaching, wool must first be scoured and silk must be degummed. Common bleaching agents used domestically are Javelle water, which is sodium hypochlorite in water, and other chlorine-based mixtures.

 
Wikipedia: bleach
This article is about the chemical whitener. For the Japanese anime and manga series, see Bleach (manga). For other uses, see Bleach (disambiguation).
Commercial chlorine bleach
Enlarge
Commercial chlorine bleach

A bleach is a chemical that removes color or whitens, often via oxidation. Common chemical bleaches include "chlorine bleach", a solution of sodium hypochlorite (NaClO), and "oxygen bleach", which contains hydrogen peroxide or a peroxide-releasing compound such as sodium perborate or sodium percarbonate. To bleach something is to apply bleach, sometimes as a preliminary step in the process of dyeing. Bleaching powder is calcium hypochlorite.

Other types of bleach

Chlorine dioxide is used for the bleaching of wood pulp, fats and oils, cellulose, flour, textiles, beeswax, and in a number of other industries.

In the food industry, some organic peroxides (benzoyl peroxide, etc.) and other agents (e.g. bromates) are used as flour bleaching and maturing agents.

Peracetic acid, ozone and hydrogen peroxide and oxygen are used in bleaching sequences in the pulp industry to produce totally chlorine free (TCF) paper.

Not all bleaches have to be of an oxidizing nature. Sodium dithionite is used as a powerful reducing agent in some bleaching formulas. It is commonly used to bleach wood pulp used to make newsprint.

Hazards and concerns

Since bleaches are strong oxidizing agents, they can be quite hazardous, especially when reacted with other common household chemicals.

Mixing sodium hypochlorite with acids like vinegar or drain cleaners containing sodium hydrogen sulfate (sodium bisulfate), or even lemon juice can release chlorine. Hypochlorite and chlorine are in equilibrium in water, the position of the equilibrium is pH dependant and low pH (acidic) favors chlorine,[1]

Cl2 + H2O Failed to parse (unknown function\rightleftharpoons): \rightleftharpoons

H+ + Cl- + HClO

Chlorine is a respiratory irritant that attacks mucous membranes and burns the skin. As little as 3.5 ppm can be detected as an odour, and 1000 ppm is likely to be fatal after a few deep breaths. Exposure to chlorine has been limited to 0.5 ppm (8-hour time-weighted average - 40 hour week) by OSHA in the US.[2]

Sodium hypochlorite and ammonia react to form a number of products, depending on the temperature, concentration, and how they are mixed. [3]. The main reaction is chlorination of ammonia, first giving chloramine (NH2Cl), then NHCl2 and finally nitrogen trichloride (NCl3). These materials are very irritating to eyes and lungs and are toxic above certain concentrations.

NH3 + NaOCl --> NaOH + NH2Cl

NH2Cl + NaOCl --> NaOH + NHCl2

NHCl2 + NaOCl --> NaOH + NCl3

Additional reactions produce hydrazine, in a variation of the Olin Raschig process.

NH3 + NH2Cl + NaOH --> N2H4 + NaCl + H2O

The hydrazine generated can further react with the monochloramine in an exothermic reaction:[1]

2 NH2Cl + N2H4 --> 2 NH4Cl + N2

Industrial bleaching agents can also be sources of concern. For example, the use of elemental chlorine in the bleaching of wood pulp produces organochlorines, persistent organic pollutants, including dioxins. However, the use of chlorine dioxide in these processes has reduced the dioxin generation to under detectable levels.[4]

History

Chlorine was first characterized by the Swedish chemist Carl Wilhelm Scheele in 1774 (as an adherent of the Phlogiston theory, he called it "dephlogisticated marine acid"). French chemist Claude Louis Berthollet, noting the bleaching properties of chlorine, invented hypochlorite bleach in 1789. In French, bleach is known as Eau de Javel, after the village where it was manufactured.

Several alternatives to bleach have recently appeared in industrialized countries. These substances are touted as being less toxic, and the use of bleach as a stain remover has become less popular in the United States. However, due to the recent upsurge of illness due to methicillin-resistant Staphylococcus aureus (known as MRSA) and other bacterial pathogens susceptible to bleach, the bleach industry has recovered somewhat, and the use of bleach as a disinfectant is increasing in a variety of industrial and commercial, as well as household settings.

Chemistry

The process of bleaching can be summarised in the following set of chemical reactions:

Cl2(aq) + H2O(l) Failed to parse (unknown function\rightleftharpoons): \rightleftharpoons

H+(aq) + Cl-(aq) + HClO(aq)

The H+ ion of the hypochlorous acid then dissolves into solution, and so the final result is effectively:

Cl2(aq) + H2O(l) Failed to parse (unknown function\rightleftharpoons): \rightleftharpoons

2H+(aq) + Cl-(aq) + ClO-(aq)

How bleaches work

Color in most dyes and pigments is produced by molecules, such as beta carotene, which contain chromophores. Chemical bleaches work in one of two ways:

  • An oxidizing bleach works by breaking the chemical bonds that make up the chromophore. This changes the molecule into a different substance that either does not contain a chromophore, or contains a chromophore that does not absorb visible light.
  • A reducing bleach works by converting double bonds in the chromophore into single bonds. This eliminates the ability of the chromophore to absorb visible light.[5]

Sunlight acts as a bleach through a process leading to similar results: high energy photons of light, often in the violet or ultraviolet range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless. Extended exposure often leads to massive discoloration usually reducing the colors to white and typically very faded blue spectrums.[6]

See also

References

  1. ^ a b Cotton, F.A; G. Wilkinson (1972). Advanced Inorganic Chemistry. John Wiley and Sons Inc. ISBN 0-471-17560-9. 
  2. ^ Occupational Safety & Health Administration (2007). OSHA -- Chlorine. OSHA. Retrieved on 2007-08-26.
  3. ^ Rizk-Ouaini, Rosette & Ferriol, Michel; Gazet, Josette; Saugier-Cohen Adad, Marie Therese (1986), "Oxidation reaction of ammonia with sodium hypochlorite. Production and degradation reactions of chloramines.", Bulletin de la Societe Chimique de France 4: 512–21
  4. ^ ECF: The Sustainable Technology. Alliance for Environmental Technology. Retrieved on 2007-09-19.
  5. ^ Field, Simon Q (2006). Ingredients -- Bleach. Science Toys. Retrieved on 2006-03-02.
  6. ^ Bloomfield, Louis A (2006). Sunlight. How Things Work Home Page. Retrieved on 2006-03-02.

Further reading

External links


This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

 
Translations: Translations for: Bleach

Dansk (Danish)
v. tr. - blege
v. intr. - bleg
n. - blegemiddel, affarvningsmiddel

Nederlands (Dutch)
bleekmiddel, (het) bleken

Français (French)
v. tr. - décolorer, oxygéner, (Phot) blanchir
v. intr. - blanchir, pâlir, oxygéner
n. - eau de Javel

Deutsch (German)
v. - bleichen, verbleichen
n. - Bleichmittel

Ελληνική (Greek)
v. - λευκαίνω, αποχρωματίζω, ασπρίζω, ξεβάφω
n. - αποχρωματισμός, λεύκανση, ξέβαμμα, λευκαντικό, (για κόμμωση) οξυζενάρισμα

Italiano (Italian)
candeggiare, scolorire

Português (Portuguese)
v. - alvejar
n. - branqueamento (m)

Русский (Russian)
отбеливать, обесцвечивать, выгорать

Español (Spanish)
v. tr. - decolorar, blanquear, aclarar el pelo, desteñir
v. intr. - descolorarse
n. - blanqueo, blanqueamiento

Svenska (Swedish)
v. - bleka, blondera, blekas, vitna
n. - blekmedel

中文（简体） (Chinese (Simplified))
漂白, 变白, 脱色, 变淡, 漂白法, 漂白剂

中文（繁體） (Chinese (Traditional))
v. tr. - 漂白
v. intr. - 變白, 脫色, 變淡
n. - 漂白, 漂白法, 漂白劑

한국어 (Korean)
v. tr. - ~을 표백하다
v. intr. - 하얗게 되다
n. - 표백[제]

日本語 (Japanese)
n. - 漂白剤
v. - 漂白する, 白くなる

العربيه (Arabic)
‏(فعل) قصر, بيض (الاسم) مادة قاصرة أو مبيضه‏

עברית (Hebrew)
v. tr. - ‮הלבין‬
v. intr. - ‮הלבין‬
n. - ‮חומר הלבנה‬

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
How Products are Made. How Products are Made. Copyright © 2002 by The Gale Group, Inc. All rights reserved.  Read more
Thesaurus. Roget's II: The New Thesaurus, Third Edition by the Editors of the American Heritage® Dictionary Copyright © 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.  Read more
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Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Bleach".  Read more
Translations. Copyright © 2007, WizCom Technologies Ltd. All rights reserved.  Read more

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