Application Technology - Oxidation and Reduction - CEBE Reinigungschemie GmbH

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Application Technology - Oxidation and Reduction

Bleaching agents may be separated into two categories: the oxidizers (that is functioning by means of oxidation) and the reducers (that is functioning by means of reduction).

Both types of bleach may be used successfully for the removal of stains. However, to use them effectively as well as safely one should have a basic understanding of how they work.
The carpet and upholstery cleaner has a different understanding of the two terms than a chemist does. We will try to bridge the gap in this article.

The first question one has to ask oneself is: why can a bleach help me with stain removal?

Counter question: why is the sky blue?

If we answer the second question we will also have answered the first. A clear sky during the day is blue because the molecules that are present in the air scatter the blue light more than they do the other colours. If one looks directly at the sun during sundown one will mainly perceive orange and red colours. These colours were not scattered but travelled directly into our eyes.

John Tyndall demonstrated this in the year 1859 when he directed a light source through a clear liquid which had particles suspended in it (milk or soap, for example). Viewed from the side the light appeared blue in colour. Viewed directly from the front the light appeared red. This led Tyndall to conclude that analogously the light was scattered by the particles in the air. Later it was actually proven that the nitrogen and oxygen molecules are responsible for the scattering of light in air. In fact, we see the colours that we see because the structure of the molecules determines which light is absorbed, scattered or or which passes through unchanged.

With stains it is basically the same thing even though somewhat more complicated, as the molecules are typically organic in nature and therefore larger than oxygen or nitrogen.

The part of an organic molecule which determines the colour is called the chromophore. If this is altered then the colour will also change. Therefore, if an oxidation or reducing agent reacts with a molecule, then the molecule may be altered so that it lets light pass through better and scatters less making the stain colourless, that is invisible!

Getting back to the difference between oxidation and reduction as a chemist would see it: a reducing agent removes an oxygen atom whereas an oxidation agent will add an oxygen atom. This change, caused by either one or the other, leads to the stain becoming colourless and thereby no longer visible to the naked eye.

There are stains, however, which may appear colourless under normal light after being treated in this manner but become visible again when exposed to UV light.

This leads to the observation that stains which have been made invisible by applying a bleach may become visible again under certain circumstances, these even being so mundane as prolonged exposure to air.

When should bleach be used?

Before considering applying a bleaching agent one should be aware of the fact that bleaches are very strong chemical agents. If used in the wrong manner they may corrode metals, remove dye that was not supposed to be removed and may also damage fibres, espcially natural ones such as cotton, wool and silk.

Bleaching agents should always be considered as a last resort when all other possibilities have been exhausted and led to limited success or failure.

Older stains especially may have caused a chemical change in the fibre thereby making the damage permanent. Or the stain may have chemically attached itself to the fibre. This may lead to more bleach being necessary to lead to success.

Before a bleaching agent is  used the area that is to be treated should be rinsed out thoroughly with water in order to remove any residual cleaning agent or stain remover. Residues may affect the reaction of the bleaching agent by either preventing it or, even worse, accelerating it!

In addition the area to be treated should be as dry as possible. The dryer it is, the more absorbent the fibres will be. This has the direct result that the dryness will increase the concentration of the belaching agent as it is not diluted by any residual moisture - thereby directly increasing its effectiveness.

Now a few words about the common bleaching agents that are used or rather their individual active ingredients.

Chlorine bleach, also known as sodium hypochlorite, is well known: it works very fast and may therefore lead to undesired colour loss. Chlorine bleach may also dissolve wool and silk and corrodes metals.

Hydrogen peroxide - contained in our product Kill Odor® OXP and also useful as a bleaching agent. It is a self-neutralizing oxidation agent. In concentrated form it may damage cotton and other natural fibres.

Sodium percarbonate: a powdered oxidation agent  which releases oxygen when it is dissolved in water. It is most effective when it is dissolved in hot water. In small amounts this reagent has a boosting affect on cleaning solutions and leads to colour enhancing/refreshing. It is contained in our additive Energizer.

Sodium perborate: a powdered oxidation agent which forms hydrogen peroxide when it is dissolved in water. This reagent is contained in our product RX for Browning. RX for Browning also contains an activator which leads to a more effective conversion of sodium perborate to hydrogen peroxide.

Oxidation agents may be accelerated through use of heat, alkalinity, and ultraviolet light.

Regarding the reducing agent side of the coin: in this case we usually deal with sulfur compounds formulated with additives. We offer three products on this basis: our Coffee Stain Remover for the removal of tannin containing stains such as coffee and tea, our Anti Brown Additive for the prevention and removal of celluslosic browning and our Reducing Agent as an individual component in our Spotting Kit.

Heat and acidity lead to an acceleration of the reaction when employing reducing agents.

Reducing agents are considerably safer to use on wool as compared to oxidation agents. These tend to have the undesired effect of accelerating and possibly even increasing the yellowing which occurs in wool.

Now that the difference between the two has been explained the question arises: when do I use an oxidation agent and when do I use a redicing agent?

A rule of thumb is that a reducing agent is always used when the stain contains colouring on an artificial basis such as food colouring, for example. Oxidation agents are correspondingly used when the colours are of a natural, organic nature.

Many stains may be removed successfully using oxidation or reducing agents. However, it is absolutely necessary to work cautiously and dilligently (in addition to having a lot of patience: applying the agent more than once is always better than applying it too strongly the first time at a high price: complete colour loss or destruction of the material).

One should, however, always start by using a conventional stain remover before resorting to employing a bleaching agent and preferably always consult us before taking the step to using a bleaching agent: we are glad to advise and assist!
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