The Science of Stain Removal

The Science of Stain Removal can be broken down into the chemical composition of stain types and detergents. This article explains the general categories of stains and the best way to approach getting the stains out based on the chemical composition.

Stain Removal Science

There are 3 Types of Stains

1. Organic Stains Explained

Organic Stains refer to stains that are created by organic compounds. Organic compounds are composed of molecules containing carbon and hydrogen and other elements, but do not include metals. 

Some organic stains are polar and others are non-polar, which essentially refers to a positive and negative charge on the molecule. Some organic stains are very long molecules and must be broken apart into shorter "chains" before the stain can be properly removed.

2. Inorganic Stains Explained

Inorganic stains or inorganic compounds that stain are not biological in origin. In other words, the compound is usually man-made or was not found in a plant or animal to begin with.

Inorganic stains are typically removed, or covered up, through the application of inorganic solvents. This is achieved through a redox reaction, where oxygen is introduced and the composition of the stain agent is chemically altered.

3. Pigments and Dye Stains Explained

Pigment stains and dye stains that contain pigment are composed of chromophores, which are molecules that contain double bonds and emit a specific wavelength of light that shows as the color of the stain. Two typical examples of pigment are wine stains (tanin) and grass stains (cholorophyll), which are both organic chromophores. These a difficult to remove stains because they don't readily respond to oxidation.

The Science of Stain Removal Explained

There are a number of different types of stain removal solutions available to treat different types of stains. The factors that impact how likely a particular solvent or detergent is to remove a stain depends on the size of the molecules, the polarity and the solubility of the molecules.

The basis rule of thumb to go by is the classic adage "Like Dissolves Like".

1. Water as a Stain Remover

Water can be used to remove stains and is generally refered to as a "universal solvent" because of it's special properties of being a bent polar molecule. This polarity makes water a great stain remover for other polar molecules and ionic compounds.

Water is an inorganic substance (no carbon), so it can only be used to dissolve other inorganic substances. With that said, water is extremely useful in delivering detergents (also known as surfactants) to the source of the stain, so is widel used in many applications of stain removal.

2. Surfactants as a Stain Remover

Surfactants (detergents) are molecules that have one polar end and one non-polar end. You can think of them like a magnet. They can help to emulsify compounds that are not usually soluble in water. For example, if you put oil in water, they tend to stay separated. If you put oil, detergent, and water together and shake them up, then you get a mixture. This is the power of a surfactant.

3. Phosphates as a Stain Remover

Phospahates are chemical compounds that have an ionic charge and contain a phosphate.

One example of how a phosphate can help to remove stains is with blood stains, which contain iron oxide. When you use iron phospate, which is a colorless, you can remove a blood stain by a chemical reaction called a displacement.

4. Acids and Bases as Stain Removers

Many soaps are bases, or basic, and can be used to remove stains that are made with basic liquids and solids. Basics are also generally polar, so they easily dissolve in water and can be used to remove stains.

There are many acids that can be used to remove stains that are created with an acidic liquid. For example, lemon juice is a common stain remover.

In short, if you know the pH of the stain, then you can select the appropriate acid or base with a similar pH level cleaner.

5. Enzymes as Stain Removers

There are many types of laundry detergents that use enzymes to help fight stains. The way that enzymes work is as follows:

 - The enzyme passes close to the stain agent

- The stain agent molecules latch onto an "active site" of the enzyme

- An enzyme/substrate complex is formed

- The enzyme breaks the stain agent molecule into smaller molecules

- The smaller molecules can be more easily dissolved and removed

Enzymes typically work well in warm water, so laundry detergents that have directions that recommend using in warm water often utilize enzymes.

6. Oxidizing Agents as Stain Removers

Oxidizing solutions like bleach are commonly employed to remove stains. Hydrogen peroxide is another example of an oxidizing agent that can remove stains.

Oxidizing agents work on stains by removing double bonds from a chromophore (e.g., ink). Through a chemical reaction (redox reaction), the double bonds become single bonds. Single bonds do not emit color, so the end result is that it looks colorless.

That is why oxidizing agents used to remove stains like bleach and hydrogen peroxide leave white spots on colored clothing, so be careful.

7. Removing Stains with using Temperature

Temperature is important because is makes molecules "excited". When stain molecules are excited, they can more easily be removed in many cases because they are moving faster. 

When the stain molecules and solution, or detergent molecules, are moving faster, it makes the stain easier to remove and also, simultaneously, more difficult to reattach.

However, too much heat can make some types of stains become "fixed" or to "set", so be sure to use caution when using heat to remove stains.

Disclaimer: This Posting was Adapted from Don, S. Effects of Chemical Constituents of Laundry Detergents and Methods of Stain Removal