Soaps & Detergents: Surfactants & Builders
Surfactants and builders are the major components of cleaning products. Other ingredients are added to provide a variety of functions, such as increasing cleaning performance for specific soils/surfaces, ensuring product stability and supplying a unique identity to a product. Let's examine how surfactants and builders work and then review other commonly used ingredients.
Surfactants, also called surface active agents, are organic chemicals that change the properties of water (see Chemistry.) By lowering the surface tension of water, surfactants enable the cleaning solution to wet a surface (e.g., clothes, dishes, countertops) more quickly, so soil can be readily loosened and removed (usually with the aid of mechanical action). Surfactants also emulsify oily soils and keep them dispersed and suspended so they do not settle back on the surface. To accomplish their intended jobs effectively, many cleaning products include two or more surfactants.
Surfactants are generally classified by their ionic (electrical charge) properties in water.
Anionic surfactants are used in laundry and hand dishwashing detergents; household cleaners; and personal cleansing products. They ionize (are converted to electrically charged particles) in solution, carry a negative charge, have excellent cleaning properties and generally are high sudsing. Linear alkylbenzene sulfonate, alcohol ethoxysulfates, alkyl sulfates and soap are the most common anionic surfactants.
Nonionic surfactants are low sudsing and are typically used in laundry and automatic dishwasher detergents and rinse aids. Because they do not ionize in solution and thus have no electrical charge, they are resistant to water hardness and clean well on most soils. The most widely used are alcohol ethoxylates.
Cationic surfactants are used in fabric softeners and in fabric-softening laundry detergents. Other cationics are the disinfecting/sanitizing ingredient in some household cleaners. They ionize in solution and have a positive charge. Quaternary ammonium compounds are the principal cationics.
Amphoteric surfactants are used in personal cleansing and household cleaning products for their mildness, sudsing and stability. They have the ability to be anionic (negatively charged), cationic (positively charged) or nonionic (no charge) in solution, depending on the pH (acidity or alkalinity) of the water. Imidazolines and betaines are the major amphoterics.
Builders enhance or maintain the cleaning efficiency of the surfactant. The primary function of builders is to reduce water hardness. This is done either by sequestration or chelation (holding hardness minerals in solution), by precipitation (forming an insoluble substance), or by ion exchange (trading electrically charged particles). Complex phosphates and sodium citrate are common sequestering builders. Sodium carbonate and sodium silicate are precipitating builders. Sodium aluminosilicate (zeolite) is an ion exchange builder.
Builders can also supply and maintain alkalinity, which assists cleaning, especially of acid soils; help keep removed soil from redepositing during washing; and emulsify oily and greasy soils.