Soap

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A handmade soap bar Handmade soap cropped and simplified.jpg
A handmade soap bar
Two equivalent images of the chemical structure of sodium stearate, a typical ingredient found in bar soaps Sodium stearate v2.svg
Two equivalent images of the chemical structure of sodium stearate, a typical ingredient found in bar soaps
Emulsifying action of soap on oil

Soap is a salt of a fatty acid (sometimes other carboxylic acids) used for cleaning and lubricating products as well as other applications. [1] In a domestic setting, soaps, specifically "toilet 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, emulsifiers, and catalysts.

Contents

Soaps are often produced by mixing fats and oils with a base. [2] Humans have used soap for millennia; evidence exists for the production of soap-like materials in ancient Babylon around 2800 BC.

Types

A collection of decorative bar soaps, as often found in hotels Decorative Soaps.jpg
A collection of decorative bar soaps, as often found in hotels

Toilet soaps

Structure of a micelle, a cell-like structure formed by the aggregation of soap subunits (such as sodium stearate): The exterior of the micelle is hydrophilic (attracted to water) and the interior is lipophilic (attracted to oils). Micelle.svg
Structure of a micelle, a cell-like structure formed by the aggregation of soap subunits (such as sodium stearate): The exterior of the micelle is hydrophilic (attracted to water) and the interior is lipophilic (attracted to oils).

In a domestic setting, "soap" usually refers to what is technically called a toilet soap, used for household and personal cleaning. Toilet soaps are salts of fatty acids with the general formula (RCO2−)M+, where M is Na (sodium) or K (potassium). [3]

When used for cleaning, soap solubilizes particles and grime, which can then be separated from the article being cleaned.The insoluble oil/fat "dirt" 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. 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. [4]

When used in hard water, soap does not lather well but forms soap scum (related to metallic soaps, see below). [5]

Non-toilet soaps

So-called metallic soaps are key components of most lubricating greases and thickeners. [3] A commercially important example is lithium stearate. 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, which would produce calcium soaps. [6] Metal soaps are also included in modern artists' oil paints formulations as a rheology modifier. [7] Metal soaps can be prepared by neutralizing fatty acids with metal oxides:

2 RCO2H + CaO → (RCO2)2Ca + H2O

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. [8]

Another class of non-toilet soaps are resin soaps, which are produced in the paper industry by the action of tree rosin with alkaline reagents used to separate cellulose from raw wood. A major component of such soaps is the sodium salt of abietic acid. Resin soaps are used as emulsifiers. [9]

Soapmaking

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 is sometimes left in the soap product as a softening agent, although it is sometimes separated. [10] [11] Handmade soap can differ from industrially made soap in that an excess of fat or (Coconut Oil, Cazumbal Process) is 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. [12] 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. [13]

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. [14] 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.

Fatty acid content of various fats used for soapmaking
Lauric acid Myristic acid Palmitic acid Stearic acid Oleic acid Linoleic acid Linolenic acid
fatsC12 saturatedC14 saturatedC16 saturatedC18 saturatedC18 monounsaturatedC18 diunsaturatedC18 triunsaturated
Tallow 0428233521
Coconut oil 481893720
Palm kernel oil 4616831220
Palm oil 014443790
Laurel oil 5400015170
Olive oil 0011278100
Canola oil 013258923

History

Proto-soaps in the Ancient world

Box for Amigo del Obrero (Worker's Friend) soap from the 20th century, part of the Museo del Objeto del Objeto collection MODOAmigo.jpg
Box for Amigo del Obrero (Worker's Friend) soap from the 20th century, part of the Museo del Objeto del Objeto collection

Proto-soaps, which mixed fat and alkali and were used for cleansing, are mentioned in Sumerian, Babylonian and Egyptian texts. [15] [16]

The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in ancient Babylon. [17] A formula for making a soap-like substance was written on a Sumerian clay tablet around 2500 BC. This was produced by heating a mixture of oil and wood ash, the earliest recorded chemical reaction, and used for washing woolen clothing. [18]

The Ebers papyrus (Egypt, 1550 BC) indicates the ancient Egyptians used a soap-like product as a medicine and created this by combining animal fats or vegetable oils with a soda ash substance called trona. [18] 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 a soap-like substance consisted of uhulu [ashes], cypress [oil] and sesame [seed oil] "for washing the stones for the servant girls". [19]

True soaps in the Ancient world

True soaps, which we might recognise as soaps today, were different to proto-soaps. They foamed, were made deliberately, and could be produced in a hard or soft form because of an understanding of lye sources. [16] It is uncertain as to who was the first to invent true soap. [15] [20]

Knowledge of how to produce true soap emerged at some point between early mentions of proto-soaps and the first century AD. [15] [16] Alkali was used to clean textiles such as wool for thousands of years [21] but soap only forms when there is enough fat, and experiments show that washing wool does not create visible quantities of soap. [15] Experiments by Sally Pointer show that the repeated laundering of materials used in perfume-making lead to noticeable amounts of soap forming. This fits with other evidence from Mesopotamian culture. [15]

Pliny the Elder, whose writings chronicle life in the first century AD, describes soap as "an invention of the Gauls". [22] The word sapo, Latin for soap, has connected to a mythical Mount Sapo, a hill near the River Tiber where animals were sacrificed. [23] But in all likelihood, the word was borrowed from an early Germanic language and is cognate with Latin sebum, "tallow". It first appears in Pliny the Elder's account, [24] 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. [25] [26] The Romans avoided washing with harsh soaps before encountering the milder soaps used by the Gauls around 58 BC. [27] 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". [28] 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. [29] The standard design is a curved blade with a handle, all of which is made of metal. [30]

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. [31]

In the Southern Levant, the ashes from barilla plants, such as species of Salsola, saltwort ( Seidlitzia rosmarinus ) and Anabasis , were used to make potash. [32] [33] Traditionally, olive oil was used instead of animal lard throughout the Levant, which was boiled in a copper cauldron for several days. [34] As the boiling progresses, alkali ashes and smaller quantities of quicklime are added and constantly stirred. [34] 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.

Ancient China

A detergent similar to soap was manufactured in ancient China from the seeds of Gleditsia sinensis . [35] 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. [36] Soap-like detergents were not as popular as ointments and creams. [35]

Islamic Golden Age

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. [37]

A 12th-century document describes the process of soap production. [38] 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 ]

Medieval Europe

Soapmakers in Naples were members of a guild in the late sixth century (then under the control of the Eastern Roman Empire), [39] and in the eighth century, soap-making was well known in Italy and Spain. [40] 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. [41] 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. [42]

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. [43] Hard toilet soap was introduced to Europe by Arabs and gradually spread as a luxury item. It was often perfumed. [37] [43]

By the 15th century, the manufacture of soap in Christendom often took place on an industrial scale, with sources in Antwerp, Castile, Marseille, Naples and Venice. [40]

16th–17th century

In France, by the second half of the 16th 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. [44] In Marseilles, by 1525, production was concentrated in at least two factories, and soap production at Marseille tended to eclipse the other Provençal centers. [45]

English manufacture tended to concentrate in London. [46] The demand for high-quality hard soap was significant enough during the Tudor period that barrels of ashes were imported for the manufacture of soap. [16]

Finer soaps were later produced in Europe from the 17th 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'. [47]

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. [48] [49] [50]

Modern period

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. [51] 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. [52]

Caricature of Lillie Langtry, from Punch, Christmas 1890: The soap box on which she sits reflects her endorsements of cosmetics and soaps. Langtry cartoon.png
Caricature of Lillie Langtry, from Punch , Christmas 1890: The soap box on which she sits reflects her endorsements of cosmetics and soaps.

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. [27] Andrew Pears started making a high-quality, transparent soap, Pears soap, in 1807 in London. [53] His son-in-law, Thomas J. Barratt, became the brand manager (the first of its kind) for Pears in 1865. [54] 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. [55] [56]

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.

Liquid soap

Liquid soap was invented in the nineteenth century; in 1865, William Sheppard patented a liquid version of soap. [57] 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. [58] This new brand of soap became popular rapidly, and to such a degree that B.J. Johnson Soap Company changed its name to Palmolive. [59]

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. [60]

See also

Related Research Articles

<span class="mw-page-title-main">Detergent</span> Surfactants with cleansing properties

A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are more soluble in hard water, because the polar sulfonate is less likely than the polar carboxylate to bind to calcium and other ions found in hard water.

<span class="mw-page-title-main">Vegetable oil</span> Oil extracted from seeds or from other parts of plants

Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of edible plants. 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 plants. In common usage, vegetable oil may refer exclusively to vegetable fats which are liquid at room temperature. Vegetable oils are usually edible.

<span class="mw-page-title-main">Margarine</span> Semi-solid oily spread often used as a butter substitute

Margarine is a spread used for flavoring, baking, and cooking. It is most often used as a substitute for butter. Although originally made from animal fats, most margarine consumed today is made from vegetable oil. The spread was originally named oleomargarine from Latin for oleum and Greek margarite. The name was later shortened to margarine.

<span class="mw-page-title-main">Tallow</span> Rendered form of beef or mutton fat

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:

<span class="mw-page-title-main">Stearin</span> Chemical compound

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).

<span class="mw-page-title-main">Cottonseed oil</span> Cooking oil

Cottonseed oil is cooking oil from the seeds of cotton plants of various species, mainly Gossypium hirsutum and Gossypium herbaceum, that are grown for cotton fiber, animal feed, and oil.

<span class="mw-page-title-main">Saponification value</span> Milligrams of a base required to saponify 1g of fat

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.

<span class="mw-page-title-main">Laundry detergent</span> Type of detergent used for cleaning laundry

Laundry detergent is a type of detergent used for cleaning dirty laundry (clothes). Laundry detergent is manufactured in powder and liquid form.

<span class="mw-page-title-main">Glycerin soap</span> Type of soap that contains glycerin, typically translucent

Glycerin soaps are soaps that contain glycerol, a component of fat or oil. They are recognizably different from other soaps because they are translucent. The clarity is due to the alignment of the soap molecules, which can be induced through the addition of alcohol and sugar. This is usually done for homemade glycerin soaps that are not remeltable.

<span class="mw-page-title-main">Pears (soap)</span> Brand of soap

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.

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.

<span class="mw-page-title-main">Cleaning agent</span> Substance used to remove dirt or other contaminants

Cleaning agents or hard-surface cleaners are substances used to remove dirt, including dust, stains, foul odors, and clutter on surfaces. Purposes of cleaning agents include health, beauty, removing offensive odors, and avoiding the spread of dirt and contaminants to oneself and others. Some cleaning agents can kill bacteria and clean at the same time. Others, called degreasers, contain organic solvents to help dissolve oils and fats.

<span class="mw-page-title-main">Tomato seed oil</span>

Tomato seed oil is a vegetable oil extracted from the seeds of tomatoes.

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.

<span class="mw-page-title-main">Hard soap</span>

Hard soaps, also termed soda soaps in older terminology, are categorized under soaps and are typically sodium salts of fatty acids. They vary in color from white to brownish and have a fatty acid content ranging from 72 to 75%. These soaps are typically made from lower-quality fats. Hard soaps serve as the foundation for products frequently labeled as fine soaps, which are fortified with nourishing additives, perfumes, and dyes.

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.

<span class="mw-page-title-main">Cooking oil</span> Oil consumed by humans, of vegetable or animal origin

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.

References

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