Laundry detergent

Builders (also called chelating or sequestering agents) are water softeners. Most domestic water supplies contain some dissolved minerals, especially in hard water areas. The metal cations present in these dissolved minerals, particularly calcium and magnesium ions, can react with surfactants to form soap scum which is much less effective for cleaning and can precipitate onto both fabric and washing machine components. Builders remove mineral ions responsible for hard water through precipitation, chelation, or ion exchange. In addition, they help remove soil by dispersion.

The earliest builders were sodium carbonate (washing soda) and sodium silicate (waterglass). In the 1930s phosphates (sodium phosphates) and polyphosphates (sodium hexametaphosphate) were introduced, continuing with the introduction of phosphonates (HEDP, ATMP, EDTMP). While these phosphorus-based agents are generally non-toxic they are now known to cause nutrient pollution, which can have serious environmental consequences. As such they have been banned in many countries, leading to the development of phosphorus-free agents, such as polycarboxylates (EDTA, NTA), citrates (trisodium citrate), silicates (sodium silicate), gluconic acid and polyacrylic acid; or ion exchange agents like zeolites.

Alkali builders may also enhance performance by changing the pH of the wash. Hydrophilic fibers like cotton will naturally have a negative surface charge in water, whereas synthetic fibers are comparatively neutral. The negative charge is further increased by the adsorption of anionic surfactants. With increasing pH, soil and fibers become more negatively charged, resulting in increased mutual repulsion. The optimum pH range for good detergency is 9–10.5.[5] Alkalis may also enhance wash performance via the saponification of fats.

Builder and surfactant work synergistically to achieve soil removal, and the washing effect of the builder may exceed that of the surfactant. With hydrophilic fibers like cotton, wool, polyamide and polyacrylonitrile, sodium triphosphate removes soil more effectively than a surfactant alone. It is expected that when washing hydrophobic fibers like polyesters and polyolefins, the effectiveness of the surfactant surpasses that of the builder, however this is not the case.[6]

Surfactants are responsible for most of the cleaning performance in laundry detergent. They provide this by absorption and emulsification of soil into the water and also by reducing the water's surface tension to improve wetting.

Laundry detergents contain mostly anionic and non-ionic surfactants. Cationic surfactants are normally incompatible with anionic detergents and have poor cleaning efficiency; they are employed only for certain special effects, as fabric softeners, antistatic agents, and biocides. Zwitterionic surfactants are rarely employed in laundry detergents mainly for cost reasons. Most detergents use a combination of various surfactants to balance their performance.

Until the 1950s, soap was the predominant surfactant in laundry detergents. By the end of the 1950s so-called "synthetic detergents" (syndets) like branched alkylbenzene sulfonates had largely replaced soap in developed countries.[7][8] Due to their poor biodegradability these branched alkylbenzenesulfonates were replaced with linear alkylbenzenesulfonates (LAS) in the mid-1960s. Since the 1980s, alkyl sulfates such as SDS have found increasing application at the expense of LAS.

Since the 1970s, nonionic surfactants like alcohol ethoxylates have acquired a higher share in laundry detergents. In the 1990s, glucamides appeared as co-surfactants, and alkyl polyglycosides have been used in specialty detergents for fine fabrics.[4]

Despite the name, modern laundry bleaches do not include household bleach (sodium hypochlorite). Laundry bleaches are typically stable adducts of hydrogen peroxide, such as sodium perborate and sodium percarbonate; these are inactive as solids but will release hydrogen peroxide upon exposure to water. The main targets of bleaches are oxidisible organic stains, which are usually of vegetable origin (e.g. chlorophyll, anthocyanin dyes, tannins, humic acids, and carotenoid pigments). Hydrogen peroxide is insufficiently active as a bleach at temperature below 60 °C (140 °F), which traditionally made hot washes the norm. The development of bleach activators in the 1970s and 1980s allowed for cooler washing temperatures to be effective. These compounds, such as tetraacetylethylenediamine (TAED), react with hydrogen peroxide to produce peracetic acid, which is an even more effective bleach, particularly at lower temperatures.[4]

The use of enzymes for laundry was introduced in 1913 by Otto Rohm. The first preparation was a pancreatic extract obtained from slaughtered animals, which was unstable against alkali and bleach. Only in the latter part of the century with the availability of thermally robust bacterial enzymes did this technology become mainstream.

Enzymes are required to degrade stubborn stains composed of proteins (e.g., milk, cocoa, blood, egg yolk, grass), fats (e.g., chocolate, fats, oils), starch (e.g., flour and potato stains), and cellulose (damaged cotton fibrils, vegetable and fruit stains). Each type of stain requires a different type of enzyme: proteases (savinase) for proteins, lipases for greases, α-amylases for carbohydrates, and cellulases for cellulose.

Many other ingredients are added depending on the expected circumstances of use. Such additives modify the foaming properties of the product by either stabilizing or counteracting foam. Other ingredients increase or decrease the viscosity of the solution, or solubilize other ingredients. Corrosion inhibitors counteract damage to washing equipment. Dye transfer inhibitors prevent dyes from one article from coloring other items, these are generally polar water-soluble polymers such as polyvinylpyrrolidone, to which the dyes preferentially bind. Antiredeposition agents such as carboxymethyl cellulose are used to prevent fine soil particles from reattaching to the product being cleaned.[4] Commercial or industrial laundries may make use of a laundry sour during the final rinse cycle to neutralise any remaining alkali surfactants and remove acid-sensitive stains.

A number of ingredients affect aesthetic properties of the item to be cleaned or the detergent itself before or during use. These agents include optical brighteners, fabric softeners, and colorants. A variety of perfumes are also components of modern detergents, provided that they are compatible with the other components and do not affect the color of the cleaned item. The perfumes are typically a mixture of many compounds, common classes include terpene alcohols (citronellol, geraniol, linalool, nerol) and their esters (linalyl acetate), aromatic aldehydes (helional, hexyl cinnamaldehyde, lilial) and synthetic musks (galaxolide).