Green Laundry Detergents and the Chemical Structure of Surfactants

A surfactant is the working molecule in a detergent mixture, or in a soap. In general surfactant molecules are long carbon chain molecules which attract water molecules, on the one end, and yet repel water molecules on the other end. There are numerous possibilities in how the surfactant molecule may be formed chemically. And, the chemical structure of surfactants will influence the manner in which that surfactant can interact with water, with minerals in the water and with the oil and dirt on the laundry. Later in this series there will be a description of how a surfactant in a laundry detergent actually works to clean the laundry but for now we will just look at the types of surfactants that may be used in the detergent and cleaning business.

Industry is always on the search for a more effective, cheaper alternative to current surfactants that are in use. At the level of laundry itself, there are several specific types of surfactants that are used. These chemical compounds are used for particular purposes. There are four main classes of surfactants used in laundry detergents. These are:

• Anionic Surfactants
• Cationic Surfactants
• Non-ionic Surfactants
• Amphoteric/Zwetterinic Surfactants

These classes of surfactant are defined according to the type of charge that the water loving head of the surfactant molecule carries. Anionic surfactants ( the most commonly used surfactants) have negatively charged water loving heads, cationic surfactants have positively charged heads, nonionic surfactants have only an electrical tendency to their water loving heads, not a full charge. Amphoteric Surfactants polar heads slip from positively charged to negatively charged depending upon the conditions.

There are many possible formations of the long carbon chain that will be attached to the water loving head of any of these types of surfactants. The nature of the carbon chain in the surfactant can have a big influence upon how well it performs its laundry functions (not all or which are cleaning) and, perhaps more importantly, what happens to the surfactant when it enters the home or the environment.

The chemical structure of anionic surfactants is ruled by the nature of the water loving heads of the molecules. In an anionic surfactant the polar (water loving) head of each molecule is negatively charged. Anionic surfactants are the most widely used type of surfactants in laundering detergents The molecules which make up ordinary bar soap (the sodium or potassium salts of saponified fatty acid chains) belong in this category of surfactant. You will be familiar with the names Sodium Lauryl Sulfate (SLS) and Sodium Laureth Sulfate (SLES). These are commonly used anionic surfactants in household cleaners and personal care products. Not all the news about this surfactant is as good as one might wish it to be, see 'Is Sodium Lauryl Sulfate a Natural Surfactant?'to find out why.

The traditional saponifed fatty acid surfactant from old fashioned soap has for many years been replaced in the laundry detergent industry (and soap market in general) by other more powerful anionic surfactants. Saponified fatty acid surfactants are easily tangled up with mineral ions in the wash water. When a surfactant molecule binds itself to a water mineral ion it can no longer act as a surfactant. It simply falls out of solution because the mineral ion cancels out the negatively charged polar end of the molecule. Deactivated anionic surfactants can be seen as soap scum in the laundry wash. Since saponified fatty acid surfactants are so much more susceptible to this action than their industrial counter parts, they have be ousted from the average laundry detergent mix by the harsher detergent surfactants that you do find in those laundry detergent mixtures today.

This is unfortunate since saponified fatty acid surfactants are simple to make and they can easily be made with ordinary, benign ingredients. The starting ingredients of these soaps are simply edible oils and ionic minerals. These soaps do not bring with them a backlog of dangerous trace impurities and their effect upon the body will be similar to the effect that their constituent ingredients would have had. The anionic surfactants that the chemical industries have replaced these soaps with, on the other hand, do carry traces of chemical manufacturing impurities and their biochemical impacts are still under investigation. The long term impact of these harsher surfactants on health and the environment is not clearly understood.

< BACK to Green Laundry Detergents: First Understand What is in Laundry Detergents