The word ‘detergent’ means any substance that cleans things. But today the word is usually used to mean synthetic or man-made detergents such as washing powders.
A detergent is an organic substance composed of carbon, oxygen, sulphur and hydrogen compounds. When combined with water it helps to clean soiled materials. The ordinary soap is a type of detergent, but it has a different chemical composition. The household detergents, used mainly for cleaning clothes and utensils, come in powder, flake or liquid form.
The first detergent was developed in 1916 by a German scientist called Fritz Gunther. Since then their use has been on the constant increase.
All the detergents contain a basic cleaning agent called a surfactant or surface-active agent. The surfactant molecules attach themselves to dirt particles in soiled materials like cloth etc. They pry the dirt particles from the cloth and surround the particles with a layer of water that allows them to be carried away. The surfactants that are made by treating beef fat or tallow with various chemicals increase the wetting ability of water by lowering its surface tension. The surface tension is the force that keeps water molecules separate and help to move deeper into soiled materials. This helps remove deep-seated dirt particles in fabrics. For example, surfactants also help detergents create lather and suds. Contrary to the popular belief, lather and suds have very little to do with the cleaning ability of a detergent.
Most of the detergents contain many other agents besides surfactants, including bleaches, fabric brighteners, builders and stabilizers. They also contain anti-redeposition agents that prevent removed dirt particles from returning to the cleaned material.
The surfactants can be divided into three main groups: anionic, which become negatively charged ions when in solution; cationic – which form positive ions in solution; and non-ionic which do not become ionized. Detergents may be anionic, cationic or non-ionic or mixture of two or more type of surfactant.
The most common synthetic surfactants used in domestic detergents are the alkyrbenzene sulphonates. These are produced by the sulphonation of an alkylbenzene. The alkylbenzene is treated with oleum to give the sulphonated alkylbenzene and sulphuric acid. The sulphuric acid is diluted with water and separated from the sulphonate, which is then neutralized with caustic soda.
Non-soap detergent powders, which contain 20-25 percent surfactant, are manufactured by spray drying a mixture of surfactant paste and the other ingredients.
The liquid detergents are produced by mixing the ingredients in liquid form, together with a hydrotrope such as sodium xylem sulphonate or potassium toulene sulphonate which ensures that the ingredients do not get separated from the mixture. Liquid detergent can reach solid areas better than soaps and do not leave deposit of dirts. The non-ionic surfactants are the ethoxylated alkylphenols. These are made by heating ethylene oxide and an alkylphenon to a temperature of 180 C in the presence of an alkaline catalyst.
Special detergent formulations are manufactured for a wide range of industrial cleaning purposes. Recently scientists have developed detergents which are broken down by bacteria at sewage works.