Soap, Detergent and cleaning Chemistry

To understand what is needed to achieve effective cleaning, there must be the need to have a basic knowledge of soap and detergent chemistry.

Water, the liquid commonly used for cleaning, has a property called surface tension. 

Water molecules are attracted each other. However, at the surface, those molecules are surrounded by other water molecules only on the water side. A tension is created as the water molecules at the surface are pulled into the body of the water. This tension causes water to bead up on surfaces (glass, fabric), which slows wetting of the surface and inhibits the cleaning process. You can see surface tension at work by placing a drop of water onto a counter top. The drop will hold its shape and will not spread.

It is this tension that enables water strikers to walk on water surface as you can see below.

In stain cleaning process, surface tension must be reduced so water can spread and wet surfaces. Chemicals that are able to do this effectively are called surface active agents, or surfactants(detergents). They are said to make water "wetter."

Surfactants perform other important functions in cleaning, such as loosening, emulsifying sinkdishes(dispersing in water) and holding soil in suspension until it can be rinsed away. Surfactants can also provide alkalinity, which is useful in removing acidic soils. 

Surfactants are classified by their ionic (electrical charge) properties in water: anionic (negative charge), nonionic (no charge), cationic (positive charge) and amphoteric (either positive or negative charge).

Soap is an anionic surfactant. Other anionic as well as nonionic surfactants are the main ingredients in today's detergents. looking closer at the chemistry of surfactants, as follow.

1.Soaps

Soaps are water-soluble alkali salts of fatty acids. Soaps are made from fats and oils, or their fatty acids, by treating them chemically with a strong alkali.

First let's examine the composition of fats, oils and alkalis; then we'll review the soapmaking process.

Fats and Oils

The fats and oils used in soapmaking come from animal or plant sources. Each fat or oil is made up of a distinctive mixture of several different triglycerides.

In a triglyceride molecule, three fatty acid molecules are attached to one molecule of glycerine. There are many types of triglycerides; each type consists of its own particular combination of fatty acids.

Fatty acids are the components of fats and oils that are used in making soap. They are weak acids composed of two parts:

A carboxylic acid group consisting of one hydrogen (H) atom, two oxygen (O) atoms, and one carbon (C) atom, plus a hydrocarbon chain attached to the carboxylic acid group as you see above. Generally, it is made up of a long straight chain of carbon (C) atoms each carrying two hydrogen (H) atoms.

Alkali

An alkali is a soluble salt of an alkali metal like sodium or potassium. Originally, the alkalis used in soapmaking were obtained from the ashes of plants, but they are now made commercially. Today, the term alkali describes a substance that chemically is a base (the opposite of an acid) and that reacts with and neutralizes an acid.

The common alkalis used in soapmaking are sodium hydroxide (NaOH), also called caustic soda; and potassium 07Chemhydroxide (KOH), also called caustic potash.

How Soaps are Made

 To be continued in the next article, but feel free to ask any question about soap and detergent quality at the comment section.