What are detergents and surfactants

Surfactants - detergents

Surfactants are substances that reduce the surface tension of water. Fats cannot be dissolved with water.
In order to still be able to wash with water, you need substances that have a water-like and a fat-like end, so that it is possible to bring non-polar (non-wettable) substances into solution with water - the surfactants.

Surfactants attach themselves to the fat-friendly (non-polar) part, lift it off the base, surround it and disperse (distribute) it. The water-friendly (polar) part faces the water and so the fat can be transported away by the water.

Soaps are salts of fatty acids, they are obtained by splitting the fats with alkalis (there are also other processes).
With NaOH it forms curd soap (solid), with KOH it forms soft soap (liquid).
The properties of the soap can be influenced by mixing different fats and oils (coarse or fine foam that lasts more or less long).


Disadvantages of the soap:

Soap has the advantage that it is more easily biodegradable than synthetic surfactants, but it also has Disadvantage:

Soap is basic- it disturbs the pH value of the skin (approx. 5.3).
- Wool and silk are damaged by alkaline solutions.
Soap forms insoluble salts with water hardness ("lime soap"):The lime soap reduces the washing effect and makes the laundry gray and hard.

In principle, synthetic surfactants have the same structure as soaps. They are usually less biodegradable than the soaps, but they do not have the disadvantages of the soaps.

A typical synthetic surfactant is for example: "Sodium lauryl sulfate" (sodium dodecyl sulfate), it is also used in toothpaste.

Surfactants are not only used in detergents, household cleaners, hair shampoos and toothpaste, but also in cosmetics and for technical purposes such as ore processing (separation of ore from other rock). Emulsifying substances ("emulsifiers") are also used in the manufacture of paints and varnishes and in the food industry.

Detergents not only contain surfactants, but also water softeners, bleaching agents, enzymes to break down protein, alkaline substances, optical brighteners, fillers, foam regulators, corrosion inhibitors (prevent corrosion of the washing machine) and fragrances.

10-20%Surfactantsas detergent substances
20-30%Softenerin the past: polyphosphates, today: zeolite (silicate), bind calcium ions of water hardness
10-20%BleachPerborate: give off atomic oxygen (like H2O2), which bleaches fruit stains, etc.
are not in color detergents included (out of consideration for the colors)
5-20%Alkalismainly well2CO3, not in mild detergents (Wool shrinks in lye)
0,1-0,3%EnzymesProteases (enzymes that break down proteins = protein)
0,1-0,2%Brightenerconvert UV light into visible light (this is why UV light is used in discos)
0,5-1%various fabricsCorrosion inhibitors, graying inhibitors, foam regulators, fragrances, etc.
Fillerskeep the mixture free-flowing

As Softener Zeolites are used today. Zeolite A consists of cage-like silicate molecules in which e.g. Ca2+ Ions are bound.
Zeolites also occur in nature, Zeolite A is produced synthetically. In contrast to the previously used polyphosphates, it is environmentally neutral.

As Bleach Na perborate is used because it decomposes above 60 ° C with the release of O radicals. The oxygen radicals destroy dyes (fruit stains, etc.) or convert them into colorless (= invisible) substances.
So-called is required so that perborates also work at temperatures below 60 ° C Bleach activators like TAED.

Detection of bleach in detergents:

If one gives to a transparent solution of KMnO4 a heavy-duty detergent, the solution becomes discolored => bleach present.
This reaction should not occur with a "color detergent".

Enzymesthat break down protein can also cause skin irritation. In the past, this mainly affected employees in detergent factories, but now the enzymes are "packaged" in wax spheres that melt in warm water and only release their contents in the lye.

Optical brighteners are substances that convert UV light into visible light. As a result, materials impregnated in this way appear whiter than their surroundings. They have a similar structure to dyes and are also used in the paper industry.

Attempt:Both white laundry and paper are "whiter than white" in the light of a UV lamp. This also works with UV lamps for tanning the skin. (Attention: do not look directly into the light, eye damage possible!)

Foam regulators are substances that prevent too much foam from being created during washing (the washing machine would foam over!). These are different surfactants.

Attempt:If you use a foam bath additive (contains surfactants) in the bathtub, you can usually observe that the foam breaks down when you use hair shampoo. It is the same phenomenon as with foam regulators in detergents: different surfactants reduce the foam of the other.