These are cleaning agents that, when used in conjunction with water loosen and remove dirt and then hold it in suspension so that the dirt is not re deposited on the cleaned surface. They can be of two types – soapy detergents and synthetic detergents (nn soapy). The three basic properties of a good detergent are:
1. Good wetting power – to lower the surface tension of water and enable the surface of the article to be thoroughly wet.
2. Good emulsifying power – to break up the grease and enable the dirt to be loosened.
3. Good suspending power – to suspend the dirt in the solution, thus preventing its re-deposition.
Composition and action of detergents
All detergents are primarily composed of three parts.
Active ingredients: – In soapy detergents, the active ingredient is obtained from natural oils and fats. These are composed of long fatty acid chains. The fatty acids commonly found in nature are the palmatic, stearic, oleic, and linoleic acids. These fatty acids occur in nature as triglycerides. The active ingredients in synthetic detergents are the surface active agents or surfactants obtained from petrochemicals.
Builders – These give bulk to the detergent. A builder is a compound that has no surface active properties but increases the efficiency of the detergent. They are added to facilitate better handling and dilution. In case of liquid detergents, the diluents can be water; in case of powders, sodium sulphate is used. Builders can be inorganic or organic. The various types of builders are
Additives- added to the detergent, these may be bleaching agents, blueing agents, fluorescent brighteners, enzymes, and so on. Optical brighteners or fluorescent brighteners help counteract the yellowing of fabrics that occurs with age. They are compounds that absorb ultraviolet light and reflect it back as blue light, creating an illusion of whiteness. Photo-activated bleaches, on the other hand, have an action that is chemical and not physical. They convert oxygen to nascent form when activated by sun light. Chelating agents are compounds capable of binding the mineral salts that make water hard. EDTA (ethylene diamine tetraacetic acid) and NTA (nitrilo triacetic acid) are chelating agents used in small amounts in detergents. They chelate calcium and magnesium salts. DTPA (diethyl triamine penta acetic acid) is used to chealte iron salts. Zeolites are also being used in some detergents. Hydrothropes help when, due to the presence of inorganic salts, the solubility of the liquid detergent decreases. Hydrothropes help to keep all the materials in solution. Enzymes such as proteases, lipases and amylases are incorporated in detergents to attack stains of different kinds. Advanced research has led to the development of enzymes that are stable up to temperatures of 60o C and a pH of 10.5-11. Their action is very slow and therefore they require a soaking time of 30 minutes or so. Perfumes are added to cover up the unpleasant smell of some synthetic detergents. Dyes, usually blue and green, are used to colour powdered detergents and make the product more attractive. Ground pumice is added to detergents to create a coarse texture so that stubborn dirt may be removed due to friction.
How detergents work
It is the surface active agents or surfactants in the detergent that are responsible for the three basic properties of detergents. Each molecule of the surfactant has a hydrophilic(wave loving) head and a hydrophobic (water heating), oleophilic (grease loving) tail. In other words, the hydrophilic head is attracted to water, whereas the hydrophobic tail is attracted by grease and repelled by water. When the detergent is added to water, the following actions take place:
Wetting action – The detergent lowers the surface tension of the water. The surfactant molecules tend to arrange themselves at the water-air interface. The hydrophobic tails of the surfactant molecules are repelled by water, creating a pull in the opposite direction to that of the inward pull of the water molecules.
Emulsifying action – The hydrophobic tails of the surfactant molecules are also oleophic in nature that is they are attracted to grease. The tails thus penetrate the grease and lift off the fabric surface. The dirt also gets lifted away as it is entrapped in the grease.
Suspending action – Since the grease molecules are entrapped by the surfactant molecules, their contact with other surfaces is prevented. The grease (with the embedded dirt) is thus held in a stable emulsion in the water. This is also partly due to the fact that the hydrophilic heads at the other end from the grease molecules are attracted to water. Most of the surfactants now carry a mild charge, that is, they ionize and repel each other. This also aids in the suspending power of the detergent.
Types of detergents
Various types of detergents are available for use in different areas and on different surfaces.
Soapy detergents/soaps – These are obtained when fat/oil is treated with an alkali. The process is called as saponification. Soaps are relatively inexpensive. Soaps are effective only in soft water; in hard water they form a scum that is difficult to rinse away. Detergents from this category used in housekeeping are:
1. Toilet soaps – They are used in different kinds of packaging for guest rooms and cloakrooms. They contain perfume, dye stuffs, and antioxidants such as vitamin E. they don’t contain any builders.
2. Soap powders – They dissolve rapidly in water and lather well, and comprise up to 40% of builders.
3. Soap flakes – The simplest form of all detergents, they dissolve easily and are used for delicate fabrics washed at lower temperatures.
Synthetic detergents – These are soap free and have replaced the use of soaps in many cleaning processes. They are not affected by hard water and have good suspending powers. Based on their chemical nature, they may be neutral detergents (anionic, non ionic, cationic or amphoteric) or alkaline detergents as we have seen above. Alkaline detergents are used in the housekeeping departments, as they are very strong detergents, ideal for removing grease.
They have a pH of 9-12.5. Though they do not foam much, they require thorough rinsing because of their slippery nature in solution. They will also patch the cleaned surface if not rinsed well. They are used on heavily soiled surfaces and for removing water-based floor polishes. Since they have such a high pH, they are harmful to the skin and therefore the staff must take special precautions while using them. However, the various categories of synthetic detergent in common use in housekeeping are:
Toilet soaps Liquid synthetic detergents
Soap powders powdered synthetic detergents
Soap flakes Solvent based detergents
1. Liquid synthetic detergents – These are light duty detergents for hard surfaces and lightly soil fabrics. They contain 20% anionic surfactants and 6-12% non-ionic surfactants. They are neutral in reaction with pH 7.0
2. Powdered synthetic detergents – These are heavy duty detergents suitable for heavily soiled fabrics. They contain 20% anionic surfactants, 2% non ionic surfactants, about 33% alkaline builders, 9% bleach, 20% fillers, SCMC (sodium carboxyl methyl cellulose), brighteners and 15%water
3. Solvent based detergents – These contain water miscible solvents, builders, and anionic solvents. Their pH is 12 and they are used for stripping spirit based wax floor polishes. They are used for cleaning areas with a heavy accumulation of grease, as in the kitchen and on machinery.
4. Biological detergents – These are powdered detergents to which enzymes have been added, they are used to remove organic stains at a temperature of 40-50o C.
5. Disinfecting detergents – These are based on cationic surfactants, mainly ‘quats’ (quaternary ammonium compounds). They have good germicidal and antistatic properties. They are available as cleaning gels, air fresheners, and fabric conditioners. They may be used on floors, walls, equipment and areas that come into contact with the food.
The ideal detergent
Different types if detergents are used according to their suitability in cleaning various surfaces. However, the selection of detergents should be based on certain criteria to ensure that the optimal detergent ids bought and the housekeeper gets value for money. An is deal detergent should – -
- Have good wetting, emulsifying powers.
- Readily dissolve in water
- Cleanse quickly with minimum agitation
- Be effective in all ranges of hard water, without producing scum
- Be effective over a wide range of temperatures.
- Be harmless to the skin and the surface to be cleaned
- Be easy to rinse away; and
- Be biodegradable
Various ‘all purpose detergents’ are now available that combine most of the above qualities. However, buying the very best detergent will be of no use if the staffs are not trained to use them in the correct way. Certain points to consider when using detergents are listed below :
- Dilute as per the manufacturer’s recommendations, using the measuring scoops and dispensers provided.
- Use the right detergent for the surface to be cleaned.
- Use protective gloves when using strong detergents.
- Dissolve the detergent thoroughly before use.
- Rinse away all traces of detergent from the surface and any cleaning equipment employed.
- Label detergent containers neatly.
- Store detergent containers in a dry, well-ventilated storage area.
- Wipe up any spilled detergent, as it may be a safety hazard.