Soaps & Detergents: Chemistry (Surfactants)
Surfactants in Detergents
A detergent is an effective cleaning product because it contains one or more surfactants. Because of their chemical makeup, the surfactants used in detergents can be engineered to perform well under a variety of conditions. Such surfactants are less sensitive than soap to the hardness minerals in water and most will not form a film.
Detergent surfactants were developed in response to a shortage of animal and vegetable fats and oils during World War I and World War II. In addition, a substance that was resistant to hard water was needed to make cleaning more effective. At that time, petroleum was found to be a plentiful source for the manufacture of these surfactants. Today, detergent surfactants are made from a variety of petrochemicals (derived from petroleum) and/or oleochemicals (derived from fats and oils).
Petrochemicals and Oleochemicals
Like the fatty acids used in soapmaking, both petroleum and fats and oils contain hydrocarbon chains that are repelled by water but attracted to oil and grease in soils. These hydrocarbon chain sources are used to make the water-hating end of the surfactant molecule.
Chemicals, such as sulfur trioxide, sulfuric acid and ethylene oxide, are used to produce the water-loving end of the surfactant molecule.
As in soapmaking, an alkali is used to make detergent surfactants. Sodium and potassium hydroxide are the most common alkalis.
How Detergent Surfactants Are Made
The chemical reacts with hydrocarbons derived from petroleum or fats and oils to produce new acids similar to fatty acids.
A second reaction adds an alkali to the new acids to produce one type of anionic surfactant molecule.
Nonionic surfactant molecules are produced by first converting the hydrocarbon to an alcohol and then reacting the fatty alcohol with ethylene oxide.
These nonionic surfactants can be reacted further with sulfur-containing acids to form another type of anionic surfactant.
How Soaps and Detergents Work
These types of energy interact and should be in proper balance. Let's look at how they work together.
Let's assume we have oily, greasy soil on clothing. Water alone will not remove this soil. One important reason is that oil and grease present in soil repel the water molecules.
Now let's add soap or detergent. The surfactant's water-hating end is repelled by water but attracted to the oil in the soil. At the same time, the water-loving end is attracted to the water molecules.
These opposing forces loosen the soil and suspend it in the water. Warm or hot water helps dissolve grease and oil in soil. Washing machine agitation or hand rubbing helps pull the soil free.