How do stain removers work?

The chemistry of stain removers, cleaners, and detergents is a rather long story. Without going into too much detail, most cleaning agents use these strategies:

1. Dissolve the stain in a solvent. This is basically how dry cleaning works. A stain made of hydrocarbons (like bicycle grease) can be removed by a hydrocarbon solvent (like gasoline). Stains from fatty substances like butter and chocolate can be removed with organic solvents. The rule is "like dissolves like": pick a solvent that is similar to your stain, and you can wash the stain out.

2. Dissolve the stain using a surfactant. Surfactants allow water to wet fabrics better, and they can surround molecules in a stain and carry them into solution.

   Soap is a surfactant; so are the sulfonates listed in the ingredients for many spot removers and carpet cleaners. A surfactant molecule contains long hydrocarbon tail with a small polar head. The hydrocarbon tail of the soap molecules surround (dissolve) grease, while the polar ends dissolve in water; the net result is that the grease/soap complex is water soluble and gets washed away. This process is called 'emulsification'. You can see it working if you add soap to some oil-and-vinegar salad dressing. The vinegar layer of the dressing gets cloudy because the soap has surrounded little droplets of oil and prevents them from rejoining the oil layer.

   Sulfonates are more often used than soap these days. They work better in 'hard' water, which causes soap molecules to precipitate from solution (forming bathtub rings and 'soap scum').

3. Eat the stain. Oxidizing agents like chlorine bleach, peroxides, and borax attack the links that hold some long-chain organic molecules in stains together. The little fragments that are left are water-soluble, and they wash away.

   Some cleaning agents contain enzymes that speed up reactions that digest proteins or fats in stains.

4. Hide the stain Some detergents contain 'whiteners' that whiten the fabric and do nothing to clean! They contain a material that absorbs ultraviolet light and re-emits it as visible light. Get a black light shine it on your clothes in a darkened room; if your laundry detergent contains whiteners, your clothes will glow!

Resources

ChemQuik (Dolphin Software)

A large database of safety information for commonly used chemicals and chemical products. The database consists of first aid, fire fighting, supplier identification, and physical properties sections abstracted from MSDS. http://www.chemquik.com/ (02/08/99)

Author: Fred Senese senese@antoine.frostburg.edu