Function: ‘Soften’ the water so it can wet the fibres and surfaces, loosen and encapsulates the dirt and prevents re-deposition of dirt on the surfaces.
Examples: Alkane sulphonates, Alcohol ethoxylates, LAS etc.
Environmental impacts: Due to their surface active nature surfactants have toxic effects on some (aquatic) organisms.
Surfactants are a large group of surface active substances with a great number of (cleaning) applications. Most surfactants have degreasing or wash active abilities. They reduce the surface tension of the water so it can wet the fibres and surfaces, they loosen and encapsulate the dirt and in that way ensure that the soiling will not re-deposit on the surfaces.
Surfactants have a hydrophobic (water repellent) part and a hydrophilic (‘water loving’) part. The hydrophobic part consists of an uncharged carbohydrate group that can be straight, branched, cyclic or aromatic.
Dependent on the nature of the hydrophilic part the surfactants are classified as an-ionic, non-ionic, cat-ionic or amphoteric.
When the hydrophilic part of the surfactant consists of a negatively charged group like a sulphonate, sulphate or carboxylate the surfactant is called anionic. Basic soaps are anionic surfactants. Over the last 50 years many soaps have been replaced with more efficient substances like alkyl sulphates, alkyl sulphonates and alkyl benzene sulphonates.
Anionic surfactants are sensitive to water hardness.
A surfactant with a non-charged hydrophilic part, e.g. ethoxylate, is non-ionic. These substances are well suited for cleaning purposes and are not sensitive to water hardness.
They have a wide application within cleaning detergents and include groups like fatty alcohol polyglycosides, alcohol ethoxylates etc.
For this category the hydrophilic part is positively charged – e.g. with a quaternary ammonium ion. This group has no wash activity effect, but fastens to the surfaces where they might provide softening, antistatic, soil repellent, anti bacterial or corrosion inhibitory effects. The most typical applications are for softeners and antistatics.
For the amphoteric surfactants the charge of the hydrophilic part is controlled by the pH of the solution. This means that they can act as anionic surfactant in an alkalic solution or as cationic surfactant in an acidic solution.
Most surfactants are more or less toxic to aquatic organisms due to their surface activity which will react with the biological membranes of the organisms.
The biological degradability varies according to the nature of the carbohydrate chain. Generally the linear chains are more readily degradable than branched chains.
Also the toxic effects vary with the chain structure. Generally an increase of the chain length in the range of 10 to 16, leads to an increase in toxicity to aquatic organisms.
The properties of surfactants most often used in laundry detergents are given below.
Specific chemical groups
Alkane sulfonates (anionic), linear alcohol ethoxylates (non-ionic) and branched alcohol ethoxylates (non-ionic)
Most of these surfactants are readily degradable with varying eco-toxicity towards aquatic organisms.
Linear alkyl benzene sulphonates – LAS (anionic)
Probably the most frequently used group of surfactants for cleaning and laundering.
Linear alkyl benzene sulphonates (LAS) have been under some debate over the recent years due to the fact that they do not biodegrade under anaerobic conditions. Under aerobic conditions LAS are readily biodegradable.
Eco-toxicity towards aquatic organisms is fairly low.
Taken and modified from an article in eco-forum
Water Rhapsody Atlantic