Soap

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Soap is a surfactant used in conjunction with water for washing and cleaning. It usually comes in a solid moulded form, termed bars due to its historic and most typical shape. The use of thick liquid soap has also become widespread, especially from soap dispensers in public washrooms. Applied to a soiled surface, soapy water effectively holds particles in suspension so the whole of it can be rinsed off with clean water. In the developed world, synthetic detergents have superseded soap as a laundry aid.

Many soaps are mixtures of sodium (soda) or potassium (potash) salts of fatty acids which can be derived from oils or fats by reacting them with an alkali (such as sodium or potassium hydroxide) at 80°–100 °C in a process known as saponification. The fats are hydrolyzed by the base, yielding glycerol and crude soap. Historically, the alkali used was potassium hydroxide made from the deliberate burning of vegetation such as bracken, or from wood ashes.

Soap is derived from either oils or fats. Sodium tallowate, a common ingredient in many soaps, is in fact derived from rendered beef fat. Soap can also be made of vegetable oils, such as olive oil. Soap made entirely from such oils, or nearly so, is called castile soap. The use of the word "soap" has become such a household name that even cleaning solutions for the body that don't have soap in the ingredients are referred to as soap.

Contents 1 Purification and finishing 2 Uses 3 The history and process of soap making 4 Handmade soap 5 Commercial soap production 6 Soap Substitutes 7 Disadvantages 8 See also 9 References 10 External links 10.1 History 10.2 Soap making 10.3 Other

[edit] Purification and finishing

The common process of purifying soap involves removal of sodium chloride, sodium hydroxide, and glycerol. These components are removed by boiling the crude soap curds in water and re-precipitating the soap with salt.

Most of the water is then removed from the soap. This was traditionally done on a chill roll which produced the soap flakes commonly used in the 1940s and 1950s. This process was superseded by spray dryers and then by vacuum dryers.

The dry soap (approximately 6-12% moisture) is then compacted into small pellets. These pellets are now ready for soap finishing, the process of converting raw soap pellets into a salable product, usually bars.

Soap pellets are combined with fragrances and other materials and blended to homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into a refiner which, by means of an auger, forces the soap through a fine wire screen. From the refiner the soap passes over a roller mill (French milling or hard milling) in a manner similar to calendering paper or plastic or to making chocolate liquor. The soap is then passed through one or more additional refiners to further plasticize the soap mass. Immediately before extrusion it passes through a vacuum chamber to remove any entrapped air. It is then extruded into a long log or blank, cut to convenient lengths, passed through a metal detector and then stamped into shape in refrigerated tools. The pressed bars are packaged in many ways.

Sand or pumice may be added to produce a scouring soap. This process is most common in creating soaps used for human hygiene. The scouring agents serve to remove dead skin cells from the surface being cleaned. This process is called exfoliation. Many newer materials are used for exfoliating soaps which are effective but do not have the sharp edges and poor size distribution of pumice.

[edit] Uses

Although the word 'soap' continues to be used informally in everyday speech and product labels, in practice nearly all kinds of "soap" in use today are actually synthetic detergents, which are less expensive and easier to manufacture. While effort has been made to reduce their negative effect upon the environment, the results have been mixed.

Soaps are useful for cleaning because soap molecules attach readily to both nonpolar molecules (such as grease or oil) and polar molecules (such as water). Although grease will normally adhere to skin or clothing, the soap molecules can attach to it as a "handle" and make it easier to rinse away. Allowing soap to sit on any surface (skin, clothes etc) over time can imbalance the moisture content on it and result in the dissolving of fabrics and dryness of skin.

(fatty end)  :CH₃-(CH₂)_n - COONa: (water soluble end)

The hydrocarbon ("fatty") portion dissolves dirt and oils, while the ionic end makes it soluble in water. Therefore, it allows water to remove normally-insoluble matter by emulsification.

[edit] The history and process of soap making

Main article: Soapmaking

The earliest known evidence of soap use are Babylonian clay cylinders dating from 2800 BC containing a soap-like substance. A formula for soap consisting of water, alkali and cassia oil was written on a Babylonian clay tablet around 2200 BC.

The Ebers papyrus (Egypt, 1550 BC) indicates that ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention that a soap-like substance was used in the preparation of wool for weaving.

It is commonly reported that a soap factory with bars of scented soap was found in the ruins of Pompeii (79 AD). However, this has proved to be a misinterpretation of the survival of some soapy mineral substance,^{[citation needed]} probably soapstone at the Fullonica where it was used for dressing recently cleansed textiles. Unfortunately this error has been repeated widely and can be found in otherwise reputable texts on soap history. The ancient Romans were generally ignorant of soap's detergent properties, and made use of the strigil to scrape dirt and sweat from the body. The word "soap" appears first in a European language in Pliny the Elder's Historia Naturalis, which discusses the manufacture of soap from tallow and ashes, but the only use he mentions for it is as a pomade for hair; he mentions rather disapprovingly that among the Gauls and Germans men are likelier to use it than women [1]

The Arabs made the soap from vegetable oil such as olive oil or some aromatic oils such as thyme oil. Sodium Lye (Al-Soda Al-Kawia) NaOH was used for the first time and the formula hasn't changed from the current soap sold in the market. From the beginning of the 7th century soap was produced in Nablus (Palestine), Kufa (Iraq) and Basra (Iraq). Soaps, as we know them today, are descendants of historical Arabian Soaps. Arabian Soap was perfumed and colored, some of the soaps were liquid and others were hard. They also had special soap for shaving. It was commercially sold for 3 Dirhams (0.3 Dinars) a piece in 981 AD. Al-Razi’s manuscript contains recipes for soap. A recently discovered manuscript from the 13th century details more recipes for soap making; e.g. take some sesame oil, a sprinkle of potash, alkali and some lime, mix them all together and boil. When cooked, they are poured into molds and left to set, leaving hard soap.

A story encountered in some places claims that soap takes its name from a supposed "Mount Sapo" where ancient Romans sacrificed animals. Rain would send a mix of animal tallow and wood ash down the mountain and into the clay soil on the banks of the Tiber. Eventually, women noticed that it was easier to clean clothes with this "soap". The location of Mount Sapo is unknown, as is the source of the "ancient Roman legend" to which this tale is typically credited.[2] In fact, the Latin word sapo simply means "soap"; it was borrowed from a Celtic or Germanic language, and is cognate with Latin sebum, "tallow", which appears in Pliny the Elder's account. Roman animal sacrifices usually burned only the bones and inedible entrails of the sacrificed animals; edible meat and fat from the sacrifices were taken by the humans rather than the gods. Animal sacrifices in the ancient world would not have included enough fat to make much soap. The legend about Mount Sapo is probably apocryphal.

Historically, soap was made by mixing animal fats with lye. Because of the caustic lye, this was a dangerous procedure (perhaps more dangerous than any present-day home activities) which could result in serious chemical burns or even blindness. Before commercially-produced lye was commonplace, it was produced at home for soap making from the ashes of a wood fire.

Castile soap, made from olive oil, was produced in Europe as early as the 16th century.

In modern times, the use of soap has become universal in industrialized nations due to a better understanding of the role of hygiene in reducing the population size of pathogenic microorganisms. Manufactured bar soaps first became available in the late nineteenth century, and advertising campaigns in Europe and the United States helped to increase popular awareness of the relationship between cleanliness and health. By the 1950s, soap had gained public acceptance as an instrument of personal hygiene.

[edit] Handmade soap

Some individuals continue to make soap in the home. The traditional name "soaper", for a soapmaker, is still used by those who make soap as a hobby or as an occupation.

The most popular soapmaking processes today is the cold process method, where fats such as olive oil react with lye. Soapmakers sometimes use the melt and pour process, where a premade soap base is melted and poured in individual molds, but this is not really to be considered soap-making. Some soapers also practice other processes, such as the historical hot process, and make special soaps such as clear soap (aka glycerin soap).

Handmade soap differs from industrial soap in that, usually, an excess of fat is used to consume the alkali (superfatting), and in that the glycerin is not removed. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap; though, if not properly formulated, it can leave users with a "greasy" feel to their skin. Often, emollients such as jojoba oil or shea butter are added 'at trace' (the point at which the saponification process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap.

[edit] Commercial soap production

Until the Industrial Revolution soap-making was done on a small scale and the product was rough. Andrew Pears started making a high-quality, transparent soap in 1789 in London. With his grandson, Francis Pears, they opened a factory in Isleworth in 1862. William Gossage produced low-price good quality soap from the 1850s in Widnes. Robert Spear Hudson began manufacturing a soap powder in 1837, initially by grinding the soap with a mortar and pestle. William Hesketh Lever and his brother James bought a small soap works in Warrington in 1885 and founded what is still one of the largest soap businesses, now called Unilever. These soap businesses were among the first to employ large scale advertising campaigns to sell the output of their factories.

[edit] Soap Substitutes

These plants are supposed to contain saponins in sufficient quantities to produce lather (when mashed plant parts are beaten in water) and can be used in either soap or shampoos.

The soap plant group (amole root, soap plant root, soaproot bulb), guaiac leaves, papaya leaves, Quillaia bark, Red campion root and leaves, Atriplex root, Sapindus fruit, soap pod fruit, Mojave yucca root, Soapwort root, Our Lord's Candle root, wild gourd fruit.^[1]

[edit] Disadvantages

Today, fat-based soaps have mostly been superseded by modern detergents. Washing agents do not contain soap for cleaning fabric, but for reducing foam.

The disadvantages of commercial soaps are:

• Most commercial soaps have had their glycerine removed for use in other industries, which deprives the skin of the natural, moisturizing glycerine and generally leaves the skin feeling dry.
• Some antibacterial soaps have antiseptic chemicals that can kill "healthy" bacteria that live symbiotically on the skin's surface and contribute to skin health. There is a theoretical risk of antibacterial additives (specifically Triclosan) in soaps contributing to antibiotic resistant bacteria, however, controlled studies have not borne out that conclusion (Aiello AE et al. Antibacterial cleaning products and drug resistance. Emerg Infect Dis 2005 Oct; 11:1565-70). Some antibacterial soaps contain Triclosan which, when discharged into the environment and exposed to sunlight, breaks down into dioxins ("Occurrence and Environmental Behavior of the Bactericide Triclosan and Its Methyl Derivative in Surface Waters and in Wastewater" Anton Lindström, Ignaz J. Buerge, Thomas Poiger, Per-Anders Bergqvist, Markus D. Müller, and Hans-Rudolf Buser Environ. Sci. Technol.; 2002; 36(11) pp 2322–2329).
• Soap-based products often contain the additive sodium laureth sulfate, which research has found to be harsh on skin. This product is also present in many non-soap cleaners for personal hygiene (shampoos, bathfoams, toothpaste, etc.).
• Soap can have a mild base reaction with fabrics, resulting in damage over the long term. This could be due to excess sodium hydroxide (NaOH, an alkali/base) left from manufacture. This, however, is highly unlikely since most soap manufacturers don't formulate their soaps to have excess lye but rather excess oil or fat. It could also be caused by the very slight presence of NaOH from the equilibrium reaction:
  R-COO-Na + H₂O ↔ R-COO^- + Na⁺ + H₂O ↔ R-COOH + NaOH
  However, this equilibrium strongly favors the left-hand side so the fraction of NaOH formed is minuscule. It could simply be that soap itself is more alkaline in general and that this, in and of itself, is the cause for the damage.
• Soap reacts with lime to form an insoluble deposit (soap scum) in "hard water":
  2Na⁺(R-COO)^-_(aq) + Ca²⁺(HCO₃^-)_2(aq) → 2Na⁺(HCO₃)^-_(aq) + Ca(R-COO)_2(s) - where R stands for an alkyl group (ppt)
• Poorly finished soaps may contain excess alkali (NaOH) and react mildly basically with skin and fabric; Most handmade and commercial products are finished to neutrality or to a weak acid content to prevent this and be more compatible with the skin's slightly acidic pH.
• Commercial products use chelating molecules (sequestrants), often EDTA derivatives to bind with any free Ca or Mg ions and prevent soap scum. These also help reduce fragrance loss, discoloration and rancidity.
• Castile soap has a very high alkalinity level, measured at about 9. pH of skin and hair has a slightly acidic pH level known to be about 5 to 6. Due to the high pH level, soapmakers who market liquid castile soap do not usually recommend it for washing hair, because it may cause hair to become dry.

[edit] See also

• Soap dispenser
• Saponin
• Unsaponifiable
• Saponification
• Soaper
• Glycerin soap
• Soapmaking
• Stainless steel soap
• Cold process
• Hot process
• Mouthsoaping

[edit] References

• Maine, Sandy (1995). The Soap Book: Simple Herbal Recipes. Interweave Press. ISBN 1-883010-14-4.
• Tarekh Al-Masoudi\the first book. [The Masoudi History-printed in 1989 Beirut-Lebanon]

[edit] External links

[edit] History

• Soap history by The Soap and Detergent Association
• The Discovery and Prehistory of Soap by R W Hedge at Butser Ancient Farm
• The History of Soap by C'etrange
• History of soap by the Pharmaceutical Journal
• Colonial Soap Making. Its History and Techniques. (The Soap Factory)
• Soap Naturally by Patrizia Garzena, contains a history of soap; rebuts the "Mount Sapo" legend.

[edit] Soap making

• Making Soap with Soap Naturally - Everything about soapmaking, including history, methods, safety, recipes, where to find ingredients.
• Soapmaking at Bellaonline - Soapmaking articles, forum and supplier links.
• Glossary for the Modern Soap Maker. Soap making terminology defined.
• The Soap Making Home Page
• Handcrafted Soap Maker's Guild
• Saponifier Magazine - Handcrafting Soaps, Toiletries & Candles (subscription only)
• Handmade Soap - Handcrafted with ancient Hawaiian techniques
• The Soap Masters - Soapmaking blog, tips and recipes

[edit] Other

• The Columbia Encyclopedia's soap entry (via Bartleby.com)
• Fight Club - Novel & movie with soap making a central theme