An understanding of Reducing agents requires an understanding of chemical color removal by the Oxidation process as well. This is because you need to know the comparative applicability of each. That is to say, "why you choose a reducer, and when", as well as knowing the potential use of both, in situations of unknown stains. Performing procedures and selection incorrectly, could advance stain setting...which happens all t0o often when your customer gets to the spot, before you do (don't be like him). In context here, the term "stain setting" is the heat or chemical transformation of a spot, wherein the resultant stain, then meets or exceeds the removal colorfastness of the fiber's original applied color dyes.
Oxidizers and Reducers
A short clinic on the differentiation and use in spotting.
Stain Guides are the preferred means for directed activity when using any reducers or oxidizers. This is because individual chemistry of reactants and accelerants vary between manufacturers of prepared products. These guides take into account these variances and give individual instruction to process so as to avoid unpredictable results.
As a general rule, spots should always be cleaned using an emulsification or solvent extraction to remove all removable components aside from actual chemical action. Heat and acidity should be avoided to ensure that spots which are not set, do not evolve into stains which are more difficult to address.
What creates color in a chemical (stain or spot)?
Chemicals that exhibit a color do so because a part of the molecules interact with light to absorb certain wavelengths, or to reflect them. They can also alter wavelengths, so that a color, which is not present in the incident light, is reflected back as changed to another color. If a chemical substance exhibits a color, the portion of the molecule that exhibits the color is called a “chromophore”
Certain molecules have an affinity to fibers, either due to physical properties, such as stickiness, particle shape, or by an electro-chemical bond. Emulsifier and solvent textile cleaning is used to break physical bonds, and suspend soil(spot) elements in water or some other solvent, so that it can be extracted by vacuum or abs
These cleaning process are sometimes ineffective if the spot contains a staining element. A staining element is a portion of the spot, which cannot be removed by emulsification or solvent cleaning.
One means to “clear” a staining element is by bleaching. A bleach alters the stain element’s chromophore in such a manner, as to then render it colorless.
Types of Bleaches
There are several types of bleach, but most fall into two classes. That being oxidizers
. Oxidizers either add oxygen or gain electrons from a reactant, while reducers remove oxygen or lose electrons to the reactant (information only, not important to know the exact distinction to be successful). The net result is that chromophore gets changed. Most chromophore "clearing" responds only to one type of bleach, or the other.
Chlorine bleach usually contains the oxidizer, sodium hypochlorite. However, due to problems with fiber degradation, unpredictable results, and residual activity, sodium hypochlorite is almost never used in carpet or upholstery spotting.
Oxygen bleach contains hydrogen peroxide or a peroxide-releasing compound
such as sodium perborate or sodium percarbonate. Other bleaching agents include sodium persulfate, sodium perphosphate, sodium persilicate, their ammonium, potassium and lithium analogs, calcium peroxide, zinc peroxide, sodium peroxide, carbamide peroxide, chlorine dioxide, bromate, and organic peroxides (e.g., benzoyl peroxide).
Most oxygen bleaches work best in hot water. Additives such as tetra acetyl ethylene diamine allow the hydrogen peroxide to work in warm water (50° C).
While most bleaches are oxidizing agents, other processes can be used to remove color. For example, sodium dithionite is a powerful reducing agent that can be used as a bleach.
How a bleach works
, like hydrogen peroxide, break the molecules at the double bond of a chromophore. This results in either a shorter molecule that does not absorb visible light, or a molecule whose chromophore is either shorter or non-existent. A shorter chromophore will absorb light of a shorter wavelength than visible light (such as ultraviolet light), and so does not appear colored.
Reducing bleaches, such as sodium bisulfite or sulfur dioxide, convert the double bonds in the chromophore into single bonds, eliminating its ability to absorb any of the visible light spectrum. Sometimes the reaction is reversible, where oxygen in the air reacts with the molecule to repair the chromophore, and the stain returns. (this why some bleaching actions require subsequent rinsing, e.g. rust stains.)
In addition to chemicals, energy can disrupt chemical bonds to bleach out color. For example, the high-energy photons in sunlight (e.g., ultraviolet rays) can disrupt the bonds in chromophores to decolorize them.
Several molecular structures and physical phenomena give rise to color or darkening on a fiber. Molecular structures containing conjugated centers of unsaturation (double bonds) such as phenols and carbonyls all cause vibration of bonds by light wavelengths, shifting absorption of light from the invisible or colorless ultraviolet range to the visible light range. By breaking up the conjugated system, colored compounds become colorless, i.e. stains become invisible. This can be accomplished by breaking or saturating the double bonds. The carbonyl groups can be reduced to alcohols, or oxidized to carboxylic acids, both colorless compounds.
When to Bleach
Bleaching is done when physical removal and emulsification cleaning has ceased to be effective
at rendering a satisfactory removal of the spot. It is said that a spot becomes a stain when chemical
alteration of the spot element is required to render the spot non-conspicuous. This does not always mean removal. Bleaching often means simple alteration of the spot element to no longer visible. The spot may still be there, but is no longer able to be seen.
The type of stain will help to determine if bleaching will be effective. Fresh stains of an organic nature with very little penetration into the fibers or pigmentation are usually successfully removed by cleaning methods without the use of bleaching. As a rule of thumb, stains, which have been in a fabric for more than three months, are usually considered 'set'. This means that usually they have successfully bonded, or reacted with the fibers to an extent that the substance is not removable or alterable.
How to Bleach
Both oxidizing bleaches and reducer bleaches are either sold as two part components, or 1-part solutions utilize the actual staining element as part of the activation media.
Oxidizing compounds are generally unstable. So packaging of product is done to minimize the off gassing of oxygen during storage. This is often accomplished through maintaining purity of relatively stable compositions, and then adding destabilizers to then cause the oxidizer to liberate the elemental oxygen, that is then free to react with the staining element.
Using a small amount of an alkaline (such as ammonia) to an oxidizer causes the release of greater amounts of oxygen. An alkaline will accelerate oxidizing bleaches.
Using a small amount of an acid (such as acetic acid) to a reducing agent hastens the reduction reaction. Acids accelerate reducing agents.
One should be aware that natural fibers like wool & cotton are susceptible to damage from chemical reactions. Sodium Percarbonate, often used for its oxidizer properties, is a fairly strong alkaline (sodium Carbonate. Alkalinity on natural fibers tends to degrade them. In these cases, using an oxidizer without a high degree of alkalinity is preferred, such as Hydrogen Peroxide. The peroxide can be accelerated with either heat or UV. U.V. is by all means to the preferred method IF the stain material is unknown.
Acceleration of bleaching action
Basic chart of known stains and first choice to remove
Betadine/Iodine (Oxidizers will often work also)
Candy (Red Food dye) **
Kool Aid (red)
Cough Syrup – red
Hi-lighter –Yellow or Green
Curry (needs accelerant)
Highlighter red or blue
Mold & Mildew stains
Dispersed Dyes (Mustard, Curry, Turmeric)
Real Fruit Juice
Toilet Bowl blue
** Require supplemental action in addition to oxidation/reduction decoloring(i.e. emulsisification and/or solvent removal).
Most any spot and staining element requires detergent and solvent preconditioning and subsequent extraction, using water as a rinse agent.
Reducing agents are often vastly improved with heat. Therefore, use of a steam iron, or a steamer is often indicated. Newer product formulations are now available that lessen the need for additional heat.
Unknown Stains and order of trial
Because heat and acidity are both part and parcel to reducing procedures, they are used LAST in any situation where you may choose to use one or both methods of bleaching. Therefore, always use the oxidizer first, and then gauge the reaction. Extract, and then use the reducing agent. OXIDIZER FIRST, THEN REDUCER
There are exceptions to this rule. Consult stain guides for individual product lines.
Example: DO NOT apply an oxidizing agent such as Hydrogen Peroxide or a high P.H. enzyme to hair dye stains. It will only intensify them.
Oxygen bleaches often work by liberating oxygen in a manner by which an effervescing does occur. effervescing is the emission of small bubbles. The physical manifestation and collapse of these bubbles create a monumental physical action at a very microscopic level. This physical action creates a great deal of movement, or agitation to soils of the 1-4 micron range. This aids greatly in removal, and is the basis for soil removal of popular processes, such as CD. This same action can be of help, in addition to oxidation, for removal of soiling such as filtration.
As discussed, alkali accelerates hydrogen peroxide’s liberation of oxygen. But almost any contaminant will cause a reaction, and not always a good one. Certain acids can have some unpredictable results if combined with hydrogen peroxide. So it is best not to experiment with any acids “on hand” in any manner, to achieve a desired effect. For example, if one uses acetic acid in an effort to accelerate hydrogen peroxide, some of the reaction will create another compound called peroxyacetic acid. Peracetic (peroxyacetic) acid is a highly corrosive organic peroxide that will bleach out most any dye, and degrade natural fibers. Many people who have used this combination literally bleach out all color and ruin the fibers.
Hydrogen peroxide and ammonium hydroxide: Ammonium hydroxide is among the fastest & controlled means to liberate the oxygen from H2O2.
The addition of heat, while many times a benefit for the action of a reducer, can be very unpredictable when used contrary to the formula's instructions. Heat used with a Reducer, on a stain far better removed by oxidation, can, in some instances, cause setting. Subsequent use of an oxidixer may then be far less effective.
Additionally, heat when used with an oxidizer can lead to partial or total color loss. One should only apply heat to an oxidizer, if the product's instructions specifically indicate that it is correct and safe to do so.
Some fibers, especially natural fibers, require very specialized oxidizers and reducers to allay chemical degradation of fibers (and dyes). Know your products, and the fibers on which they are to be used.
Never, ever, mix an oxidizer and a reducing agent together. Not only will they will not then function, the chemical reaction can be dangerous. Always thoroughly rinse the fibers after, if between switched product procedures.