This article is missing information about What determines hardness of soap and solubility to water and oil, why dissolving speed varies.(April 2024) |
Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. [1] In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are used as thickeners, components of some lubricants, and precursors to catalysts.
When used for cleaning, soap solubilizes particles and grime, which can then be separated from the article being cleaned. In hand washing, as a surfactant, when lathered with a little water, soap kills microorganisms by disorganizing their membrane lipid bilayer and denaturing their proteins.[ citation needed ] It also emulsifies oils, enabling them to be carried away by running water. [2]
Soap is created by mixing fats and oils with a base. [3] Humans have used soap for millennia; evidence exists for the production of soap-like materials in ancient Babylon around 2800 BC.
It is uncertain as to who was the first to invent soap. [4] The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in ancient Babylon. [5] A formula for making soap was written on a Sumerian clay tablet around 2500 BC; the soap was produced by heating a mixture of oil and wood ash, the earliest recorded chemical reaction, and used for washing woolen clothing. [6]
The Ebers papyrus (Egypt, 1550 BC) indicates the ancient Egyptians used soap as a medicine and combined animal fats or vegetable oils with a soda ash substance called trona to create their soaps. [6] Egyptian documents mention a similar substance was used in the preparation of wool for weaving.[ citation needed ]
In the reign of Nabonidus (556–539 BC), a recipe for soap consisted of uhulu [ashes], cypress [oil] and sesame [seed oil] "for washing the stones for the servant girls". [7]
In the Southern Levant, the ashes from barilla plants, such as species of Salsola, saltwort ( Seidlitzia rosmarinus ) and Anabasis , were used in soap production, known as potash. [8] [9] Traditionally, olive oil was used instead of animal lard throughout the Levant, which was boiled in a copper cauldron for several days. [10] As the boiling progresses, alkali ashes and smaller quantities of quicklime are added and constantly stirred. [10] In the case of lard, it required constant stirring while kept lukewarm until it began to trace. Once it began to thicken, the brew was poured into a mold and left to cool and harden for two weeks. After hardening, it was cut into smaller cakes. Aromatic herbs were often added to the rendered soap to impart their fragrance, such as yarrow leaves, lavender, germander, etc.
Pliny the Elder, whose writings chronicle life in the first century AD, describes soap as "an invention of the Gauls". [11] The word sapo, Latin for soap, likely was borrowed from an early Germanic language and is cognate with Latin sebum, "tallow". It first appears in Pliny the Elder's account, [12] Historia Naturalis , which discusses the manufacture of soap from tallow and ashes. There he mentions its use in the treatment of scrofulous sores, as well as among the Gauls as a dye to redden hair which the men in Germania were more likely to use than women. [13] [14] The Romans avoided washing with harsh soaps before encountering the milder soaps used by the Gauls around 58 BC. [15] Aretaeus of Cappadocia, writing in the 2nd century AD, observes among "Celts, which are men called Gauls, those alkaline substances that are made into balls [...] called soap". [16] The Romans' preferred method of cleaning the body was to massage oil into the skin and then scrape away both the oil and any dirt with a strigil. [17] The standard design is a curved blade with a handle, all of which is made of metal. [18]
The 2nd-century AD physician Galen describes soap-making using lye and prescribes washing to carry away impurities from the body and clothes. The use of soap for personal cleanliness became increasingly common in this period. According to Galen, the best soaps were Germanic, and soaps from Gaul were second best. Zosimos of Panopolis, circa 300 AD, describes soap and soapmaking. [19]
A detergent similar to soap was manufactured in ancient China from the seeds of Gleditsia sinensis . [20] Another traditional detergent is a mixture of pig pancreas and plant ash called zhuyizi (simplified Chinese :猪胰子; traditional Chinese :豬胰子; pinyin :zhūyízǐ). Soap made of animal fat did not appear in China until the modern era. [21] Soap-like detergents were not as popular as ointments and creams. [20]
Hard toilet soap with a pleasant smell was produced in the Middle East during the Islamic Golden Age, when soap-making became an established industry. Recipes for soap-making are described by Muhammad ibn Zakariya al-Razi (c. 865–925), who also gave a recipe for producing glycerine from olive oil. In the Middle East, soap was produced from the interaction of fatty oils and fats with alkali. In Syria, soap was produced using olive oil together with alkali and lime. Soap was exported from Syria to other parts of the Muslim world and to Europe. [22]
A 12th-century document describes the process of soap production. [23] It mentions the key ingredient, alkali, which later became crucial to modern chemistry, derived from al-qaly or "ashes".
By the 13th century, the manufacture of soap in the Middle East had become a major cottage industry, with sources in Nablus, Fes, Damascus, and Aleppo.[ citation needed ]
Soapmakers in Naples were members of a guild in the late sixth century (then under the control of the Eastern Roman Empire), [24] and in the eighth century, soap-making was well known in Italy and Spain. [25] The Carolingian capitulary De Villis, dating to around 800, representing the royal will of Charlemagne, mentions soap as being one of the products the stewards of royal estates are to tally. The lands of Medieval Spain were a leading soapmaker by 800, and soapmaking began in the Kingdom of England about 1200. [26] Soapmaking is mentioned both as "women's work" and as the produce of "good workmen" alongside other necessities, such as the produce of carpenters, blacksmiths, and bakers. [27]
In Europe, soap in the 9th century was produced from animal fats and had an unpleasant smell. This changed when olive oil began to be used in soap formulas instead, after which much of Europe's soap production moved to the Mediterranean olive-growing regions. [28] Hard toilet soap was introduced to Europe by Arabs and gradually spread as a luxury item. It was often perfumed. [22] [28] By the 15th century, the manufacture of soap in the Christendom had become virtually industrialized, with sources in Antwerp, Castile, Marseille, Naples and Venice. [25]
In France, by the second half of the 15th century, the semi-industrialized professional manufacture of soap was concentrated in a few centers of Provence—Toulon, Hyères, and Marseille—which supplied the rest of France. [29] In Marseilles, by 1525, production was concentrated in at least two factories, and soap production at Marseille tended to eclipse the other Provençal centers. [30] English manufacture tended to concentrate in London. [31]
Finer soaps were later produced in Europe from the 16th century, using vegetable oils (such as olive oil) as opposed to animal fats. Many of these soaps are still produced, both industrially and by small-scale artisans. Castile soap is a popular example of the vegetable-only soaps derived from the oldest "white soap" of Italy. In 1634 Charles I granted the newly formed Society of Soapmakers a monopoly in soap production who produced certificates from 'foure Countesses, and five Viscountesses, and divers other Ladies and Gentlewomen of great credite and quality, besides common Laundresses and others', testifying that 'the New White Soap washeth whiter and sweeter than the Old Soap'. [32]
During the Restoration era (February 1665 – August 1714) a soap tax was introduced in England, which meant that until the mid-1800s, soap was a luxury, used regularly only by the well-to-do. The soap manufacturing process was closely supervised by revenue officials who made sure that soapmakers' equipment was kept under lock and key when not being supervised. Moreover, soap could not be produced by small makers because of a law that stipulated that soap boilers must manufacture a minimum quantity of one imperial ton at each boiling, which placed the process beyond the reach of the average person. The soap trade was boosted and deregulated when the tax was repealed in 1853. [33] [34] [35]
Industrially manufactured bar soaps became available in the late 18th century, as advertising campaigns in Europe and America promoted popular awareness of the relationship between cleanliness and health. [36] In modern times, the use of soap has become commonplace in industrialized nations due to a better understanding of the role of hygiene in reducing the population size of pathogenic microorganisms. [37]
Until the Industrial Revolution, soapmaking was conducted on a small scale and the product was rough. In 1780, James Keir established a chemical works at Tipton, for the manufacture of alkali from the sulfates of potash and soda, to which he afterwards added a soap manufactory. The method of extraction proceeded on a discovery of Keir's. In 1790, Nicolas Leblanc discovered how to make alkali from common salt. [15] Andrew Pears started making a high-quality, transparent soap, Pears soap, in 1807 in London. [38] His son-in-law, Thomas J. Barratt, became the brand manager (the first of its kind) for Pears in 1865. [39] In 1882, Barratt recruited English actress and socialite Lillie Langtry to become the poster-girl for Pears soap, making her the first celebrity to endorse a commercial product. [40] [41]
William Gossage produced low-priced, good-quality soap from the 1850s. Robert Spear Hudson began manufacturing a soap powder in 1837, initially by grinding the soap with a mortar and pestle. American manufacturer Benjamin T. Babbitt introduced marketing innovations that included the sale of bar soap and distribution of product samples. William Hesketh Lever and his brother, James, bought a small soap works in Warrington in 1886 and founded what is still one of the largest soap businesses, formerly called Lever Brothers and now called Unilever. These soap businesses were among the first to employ large-scale advertising campaigns.
This section is missing information about Chemical timeline: since when did the sulfonate surfactants appear? Was the original Palmolive soap in water?.(December 2020) |
Liquid soap was not invented until the nineteenth century; in 1865, William Sheppard patented a liquid version of soap. [42] In 1898, B.J. Johnson developed a soap derived from palm and olive oils; his company, the B.J. Johnson Soap Company, introduced "Palmolive" brand soap that same year. [43] This new brand of soap became popular rapidly, and to such a degree that B.J. Johnson Soap Company changed its name to Palmolive. [44]
In the early 1900s, other companies began to develop their own liquid soaps. Such products as Pine-Sol and Tide appeared on the market, making the process of cleaning things other than skin, such as clothing, floors, and bathrooms, much easier.
Liquid soap also works better for more traditional or non-machine washing methods, such as using a washboard. [45]
Since they are salts of fatty acids, soaps have the general formula (RCO2−)nMn+, where R is an alkyl, M is a metal and n is the charge of the cation. The major classification of soaps is determined by the identity of Mn+. When M is Na (sodium) or K (potassium), the soaps are called toilet soaps, used for handwashing. Many metal dications (Mg2+, Ca2+, and others) give metallic soap. When M is Li, the result is lithium soap (e.g., lithium stearate), which is used in high-performance greases. [46] A cation from an organic base such as ammonium can be used instead of a metal; ammonium nonanoate is an ammonium-based soap that is used as an herbicide. [47]
When used in hard water, soap does not lather well and a scum of stearate, a common ingredient in soap, forms as an insoluble precipitate. [48]
Soaps are key components of most lubricating greases and thickeners. Greases are usually emulsions of calcium soap or lithium soap and mineral oil. Many other metallic soaps are also useful, including those of aluminium, sodium, and mixtures thereof. Such soaps are also used as thickeners to increase the viscosity of oils. In ancient times, lubricating greases were made by the addition of lime to olive oil. [49]
Metal soaps are also included in modern artists' oil paints formulations as a rheology modifier. [50]
Most metal soaps are prepared by hydrolysis:
In a domestic setting, "soap" usually refers to what is technically called a toilet soap, used for household and personal cleaning. [51] When used for cleaning, soap solubilizes particles and fats/oils, which can then be separated from the article being cleaned. The insoluble oil/fat molecules become associated inside micelles, tiny spheres formed from soap molecules with polar hydrophilic (water-attracting) groups on the outside and encasing a lipophilic (fat-attracting) pocket, which shields the oil/fat molecules from the water making them soluble. Anything that is soluble will be washed away with the water.
The production of toilet soaps usually entails saponification of triglycerides, which are vegetable or animal oils and fats. An alkaline solution (often lye or sodium hydroxide) induces saponification whereby the triglyceride fats first hydrolyze into salts of fatty acids. Glycerol (glycerin) is liberated. The glycerin can remain in the soap product as a softening agent, although it is sometimes separated. [52]
The type of alkali metal used determines the kind of soap product. Sodium soaps, prepared from sodium hydroxide, are firm, whereas potassium soaps, derived from potassium hydroxide, are softer or often liquid. Historically, potassium hydroxide was extracted from the ashes of bracken or other plants. Lithium soaps also tend to be hard. These are used exclusively in greases.
For making toilet soaps, triglycerides (oils and fats) are derived from coconut, olive, or palm oils, as well as tallow. [53] Triglyceride is the chemical name for the triesters of fatty acids and glycerin. Tallow, i.e., rendered fat, is the most available triglyceride from animals. Each species offers quite different fatty acid content, resulting in soaps of distinct feel. The seed oils give softer but milder soaps. Soap made from pure olive oil, sometimes called Castile soap or Marseille soap, is reputed for its particular mildness. The term "Castile" is also sometimes applied to soaps from a mixture of oils with a high percentage of olive oil.
Lauric acid | Myristic acid | Palmitic acid | Stearic acid | Oleic acid | Linoleic acid | Linolenic acid | |
---|---|---|---|---|---|---|---|
fats | C12 saturated | C14 saturated | C16 saturated | C18 saturated | C18 monounsaturated | C18 diunsaturated | C18 triunsaturated |
Tallow | 0 | 4 | 28 | 23 | 35 | 2 | 1 |
Coconut oil | 48 | 18 | 9 | 3 | 7 | 2 | 0 |
Palm kernel oil | 46 | 16 | 8 | 3 | 12 | 2 | 0 |
Palm oil | 0 | 1 | 44 | 4 | 37 | 9 | 0 |
Laurel oil | 54 | 0 | 0 | 0 | 15 | 17 | 0 |
Olive oil | 0 | 0 | 11 | 2 | 78 | 10 | 0 |
Canola oil | 0 | 1 | 3 | 2 | 58 | 9 | 23 |
A variety of methods are available for hobbyists to make soap. [54] Most soapmakers use processes where the glycerol remains in the product, and the saponification continues for many days after the soap is poured into molds. The glycerol is left during the hot process method, but at the high temperature employed, the reaction is practically completed in the kettle, before the soap is poured into molds. This simple and quick process is employed in small factories all over the world.
Handmade soap from the cold process also differs from industrially made soap in that an excess of fat or (Coconut Oil, Cazumbal Process) are used, beyond that needed to consume the alkali (in a cold-pour process, this excess fat is called "superfatting"), and the glycerol left in acts as a moisturizing agent. However, the glycerine also makes the soap softer. The addition of glycerol and processing of this soap produces glycerin soap. Superfatted soap is more skin-friendly than one without extra fat, although it can leave a "greasy" feel. Sometimes, an emollient is added, such as jojoba oil or shea butter. [55] Sand or pumice may be added to produce a scouring soap. The scouring agents serve to remove dead cells from the skin surface being cleaned. This process is called exfoliation.
To make antibacterial soap, compounds such as triclosan or triclocarban can be added. There is some concern that use of antibacterial soaps and other products might encourage antimicrobial resistance in microorganisms. [56]
Glycerol, also called glycerine or glycerin, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pharmaceutical formulations. Because of its three hydroxyl groups, glycerol is miscible with water and is hygroscopic in nature.
Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are mixtures of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fats from seeds. Olive oil, palm oil, and rice bran oil are examples of fats from other parts of fruits. In common usage, vegetable oil may refer exclusively to vegetable fats which are liquid at room temperature. Vegetable oils are usually edible.
Tallow is a rendered form of beef or mutton suet, primarily made up of triglycerides.
Saponification is a process of cleaving esters into carboxylate salts and alcohols by the action of aqueous alkali. Typically aqueous sodium hydroxide solutions are used. It is an important type of alkaline hydrolysis. When the carboxylate is long chain, its salt is called a soap. The saponification of ethyl acetate gives sodium acetate and ethanol:
Stearin, or tristearin, or glyceryl tristearate is an odourless, white powder. It is a triglyceride derived from three units of stearic acid. Most triglycerides are derived from at least two and more commonly three different fatty acids. Like other triglycerides, stearin can crystallise in three polymorphs. For stearin, these melt at 54 (α-form), 65, and 72.5 °C (β-form).
Glycerides, also known as acylglycerols, are esters formed from glycerol and fatty acids, and are generally very hydrophobic.
Saponification value or saponification number represents the number of milligrams of potassium hydroxide (KOH) or sodium hydroxide (NaOH) required to saponify one gram of fat under the conditions specified. It is a measure of the average molecular weight of all the fatty acids present in the sample in form of triglycerides. The higher the saponification value, the lower the fatty acids average length, the lighter the mean molecular weight of triglycerides and vice versa. Practically, fats or oils with high saponification value are more suitable for soap making.
Crisco is an American brand of shortening that is produced by B&G Foods. Introduced in June 1911 by Procter & Gamble, it was the first shortening to be made entirely of vegetable oil, originally cottonseed oil. Additional products marketed under the Crisco brand include a cooking spray, various olive oils, and other cooking oils, including canola, corn, peanut, sunflower, and blended oils.
Whale oil is oil obtained from the blubber of whales. Oil from the bowhead whale was sometimes known as train-oil, which comes from the Dutch word traan.
The smoke point, also referred to as the burning point, is the temperature at which an oil or fat begins to produce a continuous bluish smoke that becomes clearly visible, dependent upon specific and defined conditions. Smoke point values can vary greatly, depending on factors such as the volume of oil utilized, the size of the container, the presence of air currents, the type and source of light as well as the quality of the oil and its acidity content, otherwise known as free fatty acid (FFA) content. The more FFA an oil contains, the quicker it will break down and start smoking. The lower the value of FFA, the higher the smoke point. However, the FFA content typically represents less than 1% of the total oil and consequently renders smoke point a poor indicator of the capacity of a fat or oil to withstand heat.
Melt and Pour soap crafting is a process often used by soapmakers, both for large scale (commercial) and small scale manufacture. Small scale artisan soap makers find "melt and pour" production useful when trying out new product lines. The process differs from the cold process or hot process in utilising a pre-manufactured solid soap base which has already undergone saponification, so the soap maker does not need to handle caustic alkali, i.e. lye.
Pears Glycerin soap is a British brand of soap first produced and sold in 1807 by Andrew Pears, at a factory just off Oxford Street in London. It was the world's first mass-market translucent soap. Under the stewardship of advertising pioneer Thomas J. Barratt, A. & F. Pears initiated a number of innovations in sales and marketing. English actress and socialite Lillie Langtry was recruited to become the poster-girl for Pears in 1882, and in doing so she became the first celebrity to endorse a commercial product.
Marseille soap or Savon de Marseille is a traditional hard soap made from vegetable oils that has been produced around Marseille, France, for about 600 years. The first documented soapmaker was recorded from the city in about 1370. By 1688, Louis XIV introduced regulations in the Edict of Colbert limiting the use of the name Savon de Marseille to olive oil based soaps. The law has since been amended to allow other vegetable oils to be used.
Oleochemistry is the study of vegetable oils and animal oils and fats, and oleochemicals derived from these fats and oils. The resulting product can be called oleochemicals (from Latin: oleum "olive oil"). The major product of this industry is soap, approximately 8.9×106 tons of which were produced in 1990. Other major oleochemicals include fatty acids, fatty acid methyl esters, fatty alcohols and fatty amines. Glycerol is a side product of all of these processes. Intermediate chemical substances produced from these basic oleochemical substances include alcohol ethoxylates, alcohol sulfates, alcohol ether sulfates, quaternary ammonium salts, monoacylglycerols (MAG), diacylglycerols (DAG), structured triacylglycerols (TAG), sugar esters, and other oleochemical products.
In the food industry and biochemistry, interesterification (IE) is a process that rearranges the fatty acids of a fat product, typically a mixture of triglycerides. The process implies breaking and reforming the ester bonds C–O–C that connect the fatty acid chains to the glycerol hubs of the fat molecules. The reactions involve catalysts, either inorganic chemicals or enzymes.
A diglyceride, or diacylglycerol (DAG), is a glyceride consisting of two fatty acid chains covalently bonded to a glycerol molecule through ester linkages. Two possible forms exist, 1,2-diacylglycerols and 1,3-diacylglycerols. Diglycerides are natural components of food fats, though minor in comparison to triglycerides. DAGs can act as surfactants and are commonly used as emulsifiers in processed foods. DAG-enriched oil has been investigated extensively as a fat substitute due to its ability to suppress the accumulation of body fat; with total annual sales of approximately USD 200 million in Japan since its introduction in the late 1990s till 2009.
Palmolive is an American multinational brand of a line of products produced by Colgate-Palmolive. The Palmolive brand grew from one product, Palmolive bar soap. Made of coconut, palm and olive oils, Palmolive bar soap was introduced in 1898. Originally, the bar soap floated like Procter & Gamble's Ivory bar soap. By the turn of the 20th century, Palmolive bar soap was the world's best-selling soap.
Saltwater soap, also called sailors' soap, is a potassium-based soap for use with seawater. Inexpensive common commercial soap will not lather or dissolve in seawater due to high levels of sodium chloride in the water. Similarly, common soap does not work as well as potassium-based soap in hard water where calcium replaces the sodium, making residual insoluble "scum" due to the insolubility of the soap residue. To be an effective cleaning agent, soap must be able to dissolve in water.
Cooking oil is a plant or animal liquid fat used in frying, baking, and other types of cooking. Oil allows higher cooking temperatures than water, making cooking faster and more flavorful, while likewise distributing heat, reducing burning and uneven cooking. It sometimes imparts its own flavor. Cooking oil is also used in food preparation and flavoring not involving heat, such as salad dressings and bread dips.
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BCE in ancient Babylon.
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: CS1 maint: location missing publisher (link)British actress Lillie Langtry became the world's first celebrity endorser when her likeness appeared on packages of Pears Soap.
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: CS1 maint: multiple names: authors list (link)Modern toilet soaps and detergents trace their origin to the ancient use of plants, commonly referred to as soapy plants, which possess foaming ability when they are agitated in water.