Soaps

This article is about a common cleaning compound. For other uses of the word Soap, see Soap (disambiguation).

Soap is a surfactant cleaning compound used for personal or minor cleaning. It usually comes in solid moulded form, termed bars. In somewhat recent years, the use of thick liquid soap has been becoming increasingly more widespread, especially from dispensers in public washrooms. Soap is used in conjunction with water for washing and cleaning. The wet soap residue and the dirt or soil are rinsed off with clean water afterwards. In the developed world, synthetic detergents have superseded soap as a laundry aid.

Many soaps are mixtures of sodium or potassium 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 potash made from the deliberate burning of vegetation such as bracken, or from wood ashes.

Soap most commonly appears in bar form. This particular bar of soap has seen some use and thus has lost its "bar" shape.

Soap is derived from either oils or fats. Sodium Tallowate, a common ingredient in many soaps, is in fact derived from rendered animal fat. Soap that is made of vegetable oils, such as olive oil, are generally termed castile soap.

Purification and finishing

The common process of purifying soap involves removal of sodium chloride, sodium hydroxide, and glycerol. These impurities 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 This process was superseded by spray dryers and then by vacuum dryers.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 content) is then compacted into small pellets. These pellets are now ready for soap finishing. Soap finishing is the process of converting raw soap pellets into 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.

Use

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, more effective, 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 cleansing 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.

(water soluble end)

CH₃-(CH₂)_n - COONa

(fatty 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.

The history and process of soap making

1922 magazine advertisement for Palmolive Soap

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.

A soap factory with bars of scented soap was found in the ruins of Pompeii (79 AD). However, the ancient Romans were generally innocent of soap's detergent properties. 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 as olive oil or some aromatic oils such as 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 made and was produced in Nablus(Palestine), Kufa(Iraq)and Basra(Iraq). Arabian Soap was perfumed and coloured some of the soaps was liquid and other was hard and there was shaving soap. It was commercially sold for 3 Dirhams (0.3 Dinars) apiece in (981 AD).

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 a hoax.

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.

Handmade soap

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. Those who make their own soaps are also known as soapcrafters.

The most popular soapmaking processes today is the cold process method, where fats such as olive oil react with lye. Novice soapmakers sometimes use the melt and pour process, where no actual soap is made, but where industrial soap base, known an glycerin, is melted and poured in individual shapes. Some soapers also practice other processes, such as the historical hot process, and make special soaps such as 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 can leave the user with a "greasy" feel to his skin. Often emollients such as jojoba oil or shea butter are added at trace, after most of the oils have saponified, so that they remain unreacted in the finished soap.

Disadvantages

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

The disadvantages of commercial soaps are:

• Soap deprives the skin of natural, beneficial oils
• Some antibacterial soaps have chemicals which actually kill some skin cells.
• Soap-based products often contain the additive sodium laureth sulfate, a chemical some believe to be harmful.
• Soap can react mildly basically with fabrics resulting in damage over the long term. This is usually due to excess sodium hydroxide (NaOH, an alkali/base) left from manufacture, but can 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
• 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)

Commercially made bar soaps are formulated to mitigate all of these disadvantages:

• A wide variety of emollient materials, such as shea or cocoa butters, are substantive to the skin.
• Poorly finished soaps contain alkali (NaOH) and react mildly basically with skin and fabric; 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, discolouration and rancidity.

See also

• Saponin
• Unsaponifiable
• Soapmaking

References

• Maine, Sandy (1995). The Soap Book: Simple Herbal Recipes. Interweave Press. ISBN 1883010144.
• Tarekh Al-Masoudi\the first book. [The Masoudi History-printed in 1989 Beirut-Lebanon]

External links

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 Gardena, contains a history of soap; rebuts the "Mount Sapo" legend.

Soap making

• Glossary for the Modern Soap Maker. Soap making terminology defined.
• How To Make Homemade Soap
• The Soap Making Home Page
• Handcrafted Soap Maker's Guild
• Soap Making Instructions

Other

• The Columbia Encyclopedia's soap entry (via Bartleby.com)