How does a detergent work?

A detergent is a chemical compound that removes “soil”
The term “SOIL” refers to any stain or dirt that has to be removed.

Chemical cleaning compounds are based on detergent concentrates produced through a process called sulphonation and are referred to as sulphonates.

These are the primary ingredients used in household detergency products. Detergents are biodegradable which means that after use they break down biologically so that the environment does not become polluted.

There is a natural “SURFACE TENSION” between grease and water. This is where the old saying of “oil and water don’t mix” comes from. The main function of a detergent is to break down the surface tension that exists between grease and water. They are referred to as “surface active agents” or ”surfactants”. Another function is to remove the dirt (or SOIL) in question.

This dirt usually comes as:

1. Soluble salts (sodium chloride is an example).
2. Common dirt such as dust or soot.
3. Oils and fats

The soluble salts can easily be removed by soaking but grease may hold the dirt on to the fiber or surface. Agitation will not be sufficient to remove the dirt so a “surface active agent” must be used to assist removal.

Detergents have millions of molecules of electrically charged particles called ions, when dissolved in water. These molecules consist of two parts, Hydrophophic and Hydrophilic. The hydrophobic is the organic hydrocarbon part of the molecule and does not like water but dissolves easily in grease. The Hydrophilic is the sulphonate part of the molecule and dissolves easily in water.

How does a detergent work?

There is a “surface tension” to water with the molecules lining up. On dissolving detergent in the water the surface tension is broken down and the molecules separate into small spheres called micelles. The spheres can hold hydrophobic dirt and oil particles as they escape into suspension. Manual or mechanical agitation is necessary to obtain best results. Surfactants: Are produced by different processes. Alcohols are derived from Coconut oil, Sodium Lauryl Sulphate and petroleum derived fractions combined with benzene, sulphonated with sulphuric acid. These surfactants are normally used combined with acid, alkaline salts or solvents in formulas aimed at a specific need.
Four major types of surfactants are:
1. Nonionic.
2. Anionic.
3. Cationic.
4. Amphoteric.

Nonionic: This is the most commonly used surfactant and there are many types. They are made by combining ethylene oxide molecules derived from petroleum fractions into water soluble polymers that reconnect to a water insoluble molecule.

Anionic: The negative charged part of the molecule is known as an ANION. In an Anion is the active part of the surfactant. The properties of the surfactant are determined by the size of its petroleum fractions. The most commonly used anionic surfactants are made up by the action of concentrated sulphuric acid on benzene derivatives and is known as SULPHONIC ACID.

Cationic: In this surfactant the cation is the positively charged portion of the molecule and is the active part. The most commonly used cationic are the h atoms are replaced by many different kinds of organic groups. Cationic surfactants are generally poor cleaners but are widely used as germicides, fabric softeners and Antistatic agents.

Amphoteric: Hawley’s condensed Chemical Dictionary describes this surfactant as “having the capacity of behaving either as an acid or a base”. Amphoteric Depending on the conditions under which they are used they may react to either acids or alkalis.

Use of Detergents in Cleaning Surfaces

The types pf surfaces to be cleaned are endless and range from engines, machinery, floors, walls, etc. through to dishes, carpets, fabric, etc…
The smoothness of the surface will affect the ability to clean. A rough or pitted surface tends to trap dirt and will therefore be more difficult to clean than a smooth surface.
The most commonly used solvent is water. Water by itself is a poor wetting agent as many common soils (such as proteins and grease) are insoluble in water. The addition of a surfactant to the water enables the water to remove the soil.

The “wet ability” of the surface must be considered. In the case of woven fabrics it is very important for the detergent and water solution to penetrate the fibers. Cotton is an easily wetted material but materials like nylon and polyester are very hydrophobic. This means that they repel water and should be washed frequently and not allowed to become too heavily soiled.

The greater the movement between the cleaning agent and the surface, the better the detergent will work. Examples of this are mechanical agitation (a washing machine), a movement of the solvent when a detergent is sprayed (a dish-washing machine) or by manual cleaning (scrubbing).

Temperature can also affect the time it takes for a detergent to work. With some products heat will assist the process. With other soils such as blood and egg stains (protein) it is best to use cold water since heat will make them sticky.

Powdered Alkaline Cleaners: Powdered alkaline cleaners are blends of alkaline salts. Each salt has a specific cleaning property. Brief examples of these properties are as follows.

Sodium Hydroxide: Sodium Hydroxide is sometimes called Caustic Soda or Lye. It is added to neutralize acidic soil. It should never be used in the presence of Aluminum as it attacks that metal.

Sodium Silicate: Added to disperse solids and assist detergency. The silicate softens the water and keeps the alkalinity level high. It protects the metal parts of a washing machine from corrosion.

Trisodium Phosphate: Also known as TSP. Assists in peptizing (dispersing into a colloidal state) the soil.

Tripolyphosphate: Also known TPPP. A conditioner that softens the water and therefore assists the organic surfactant and aids rinse ability.

Sodium Tripolyphosphate: Also known as STPP. A very commonly used phosphate as an ingredient in laundry powders. On hydrolysis it yields TSP and TSPP.

Sodium Sulphate: Its function is to keep the powder mixture dry (and not going “tacky”) by keeping the granules separated for the purpose of easypouring and freeflowing.

Sodium Perborate: When dissolved in water releases hydrogen peroxide producing small bubbles of oxygen which remove stain discoloration without affecting the fabric or damaging the colors of the material.

Author: Johan Bosman

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