In this article, we will discuss about the Cleaning action of soap, History of soap, Types of Soaps, important uses of soap etc.
The washing industry usually known as soap industry, has roots over 2000 years in the past. The present soap was gradually developed from the crude mixtures of alkaline and fatty materials. The old process known as the Batch process in which a bulk of fatty acids is treated with caustic alkali in the reaction kettles.
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| Soap |
In old days the alkali required for manufacture of soap was obtained by the crude latching of wood ashes or from evaporation of naturally occurring alkaline waters. Lablane developed a method of preparation of lower priced, sodium carbonate from sodium chloride.
After First World War, due to the shortage of raw materials led the German people to develop synthetic soaps or detergents, but has come to common use recently.
History of soap:
Soap requires two major raw materials; fat and alkali. The alkai most commonly used today is sodium hydroxide or potassium hydroxide. Potassium based soap creates a more water-soluble product than sodium-based soaps, and so it is called 'soft soap'. Soft soap, alone or in combination with sodium-based soap, is commonly used in shaving products.
Animal fat in the past was obtained directly from a slaughterhouse. Modern soap makes use fat has been processed into fatty acids. This eliminates many impurities and it produces byproduct water instead of glycerin. Many vegetable fats including olive oil, palm kernel oil and coconut oil, are also used in soap making.
The first fatty alcohol used in production of synthetic detergents were derived from body of the sperm or bottlenose whale (sperm oil).
Chemistry of soap:
soap and detergents are essential to personal and public health. They safely remove germs, soil and other contaminants and help us to stay healthy and make our surroundings more pleasant. Soaps are made from fats and oils or their fatty acids.
Fatty acids are merely carboxylic acids consisting of a long hydrocarbon chain at one end and a carboxyl group at the other end. They are generally represented as R-COOH. They are an important component of plants, animals and other microorganisms. They are found in various parts of the body, such as cell membranes, the nervous system and as lung surfactant.
The long chain fatty acids can be of either plant origin or animal origin. In general fats/ oils, soya from plant origin are high in unsaturated and low in saturated fatty acids. Fats/ oils from animal source are high in saturated and low in unsaturated fatty acids.
Raw materials for Soaps:
The triglycerides are the basic raw material for the manufacture of soap utilizing a variety of processes. The raw materials required for soap can be classified under following categories-
1) Oils and fats:
The principal raw materials required for soaps are oils and fats or fats fatty acids. The main sources of slow lathering hard oils are tallow, plam oil, whale oil, fish oil, greases etc. Quick lathering hard oils include coconut oil, inedible olive oil etc.
2) Caustic soda:
It is available in the form of flakes, blocks and sticks as well as 70° (90.32% NaOH), 72° (92.9% NaOH) and 74° (94.98% NaOH). In soap making, blocks form of NaOH is generally employed. Special quality soft soaps, shaving creams etc. make use of caustic potash (KOH) of 18.5 to 20% strength.
3) Resin:
It is a plant education product which mainly contains abietic acid. The colourless variety of resin is used in the manufacture of laundry soaps and dark variety is used in the manufacture of Coloured soaps.
4) Common salt or Sodium chloride:
It is used for salting out of soap. About 12.5 parts of common salt per 100 parts of oil to be used for Saponification.
5) Binding materials:
The cleaning capacity of ordinary soaps is improved by adding certain binding materials such as- sodium silicate, soda ash, tri-sodium phosphate and borax. The binding materials improve soap texture, correct the alkanility of the solution and prevent the formation of precipitates in hard water.
6) Fillers:
The bulk or weight of soap is increased by adding certain fillers such as talc, starch, glauber salt, pearl ash etc;without effecting the detergency.
7) Colouring matter:
Organic dyes and inorganic pigments are generally used for bar and flake soap products. As a soap dye, the colouring matter should be -
* inert to alkali used in making soap.
* should not separate out on cooling the blended soap.
* should not affect the fragrance of the soap.
Important uses of Soaps:
1) Soaps are mainly used as surfactants for washing, bathing and cleaning. They safely remove germs, soils and other contaminants and help us to stay healthy, and make our surrounding more pleasant.
2) They are also used in textile spinning and are important components of lubricants.
3) Soaps are key components of most lubricating greases, which are usually emulsions of calcium soap or lithium soaps and mineral oil.
4) Metallic soaps of aluminum and sodium are used as thickners to increase the viscosity of oils.
5) Soaps are very important for effective for hand washing and hygiene; but if it is not available in difficult situations, then clean ash or sand/ soil can be used as substitute as recommended by e.g.World Health Organization (WHO).
Purification process:
The crude soap obtained from the Saponification reaction contains 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. After the purification process is repeated several times, the soap may be used as an inexpensive industrial cleanser.
Soap is an excellent cleanser because it's ability to act as an emulsifying agent. An emulsifier is capable of dispersing one liquid into another immiscible liquid. This means that while oil does not naturally mix with water, soap can suspend oil/ dirt in such a way that it can be removed.
Types of Soaps:
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| Types of soap |
A) Nature of Alkali:
Depending upon the nature of alkali used in the production of soap, they are classified into two types: Hard soap and soft soap.
1) Hard Soap:
The Sodium salt of long chain fatty acid is known as hard soap. It is difficult to dissolve in water. It is used as laundry soap.
2) Soft Soap:
The Potassium salt of long chain fatty acid is known as soft, as it produces more lather. It is used as toilet soap and shaving soap.
B) Kinds of use:
Depending upon the usages soaps are classified into different types:
1) Kitchen soaps:
a) Cleanser: They often made with mild abrasives and are formulated to eliminate heavy oil or solid particles and hard to remove stains. Some cleanser are more abrasive than others, the mildest being cream cleaners to the harshet being powdered cleansers.
b) Dish detergent: They are made to remove tough grease and release the solid dirt particles in the foam that is produced by the detergent. Hand dishwashing detergents are made to work at lower temperatures and usually have more grease removing capacity by producing more foam. Machine dishwasher detergents are formulated to produce less foam and work at higher temperatures.
2) Laundry Soaps:
Laundry soaps are formulated to eliminate grease, solid particles and organic compounds from cloth. They are formulated to work under varying conditions. They can be found in liquid, powder and gel forms, and can work in all water and temperatures. Laundry detergents are most effective when used in warm or hot water especially when removing grease or heavy oil.
3) Cleaning soaps:
Cleaning soaps are made for cleaning soils and grease. Cleaning soaps come in light to heavy duty formulations and are great at removing soils and grease without having to use harsh abrasives.
4) Industrial Soaps:
Industrial soaps are formulated for specific tasks. They are commonly used for car washers, auto centres, and production line clean up. These soaps usually come in 55 gallon drums or large containers and are connected to pressure cleaning systems.
5) Medicated soaps:
Medicated soaps and original soaps are very similar. Unlike original soap, medicated soap has the addition of antiseptics and disinfectants or anti-bacterial agents like phenol, cresol, Halogeneted carbanilides. They suppress the growth of gram-positive bacteria.
6) Personal Soaps:
This kind of soap is made in many forms and special formulations for specific personal hygiene needs.
7) Novelty Soaps:
Novetly soaps are especially manufactured for the kids and include the soaps in the shapes of various items such as a rubber ducky or the soap on the rope. They are made not only to clean dirt and grime, but for amusement and enjoyment as well.
8) Perfumed Soaps:
Perfumed soaps are produced by adding a few additional ingredients and perfume. This soap counts as a potential source of skin irritation for allergic people.
9) Guest Soaps:
Guest soaps are miniature soaps that are made and shaped into attractive shapes. These are basically meant for use by the guests either in the main bathroom or separate guest bathroom. Flowers, sea shells and rounds are some popular and commonly used shapes for guest soaps.
10) Beauty Soaps:
Beauty soaps are produced to feature attractive fragrances and ingredients for a variety of skin types. They can feature glycerin or special oil blends.
11) Transparent soap:
Transparent soap uses slightly different ingredients and usually some form of alcohol to alter the process which is also conducted at higher temperatures. Not all transparent soaps are glycerin soaps. e.g. Pears soap.
12) Liquid Soaps:
Liquid soaps are actually very difficult to produce and many of the commercial liquid soaps are just in fact detergents.
13) Floating soaps:
These soaps are made by bubbling air through the molted neat soap until the amount of air incorporated increases its volume to such and extent that the solid soap becomes lighter than water. It contains about 30% water. e.g.Lecancy soap.
Chemical Reaction:
Soaps are sodium or Potassium salts of long chain ratty acids. When triglycerides in fat /oil react with aqueous NaOH or KOH they are converted into soap and glycerol. This is called alkaline hydrolysis of esters. Since this reaction leads to the formation of soap, it is called the Saponification process.
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| Saponification process |
The Saponification reaction is exothermic in nature, because heat is liberated during the process. The soap formed remains in suspension form in the mixture. Soap is precipitated as a solid from the suspension by adding common salt to the suspension. This process is called Salting out of soap. The water layer is drawn off the top of the mixture and glycerol is recovered using vaccum distillation.
