SOAPS AND LAUNDRY PRODUCTS:AUTOMA TICDISHWASHING DETERGENTS.

AUTOMA TICDISHWASHING DETERGENTS

First developed in the 1950s, automatic (machine) dishwashing deter- gents, in addition to removing soils originating from food particles and holding the particles in suspension, sequester minerals that contribute to water hardness, emulsify greasy oils, and assist in allowing water to rinse off dishes via a sheeting action. Generally, these detergents are quite caustic, and their efficiency can depend on their physical characteristics (e.g., granular powder). A typical powder-based formulation contains 30 per- cent anhydrous sodium tripolyphosphate (Na5P3O10), 30 percent anhydrous sodium metasilicate (Na2SiO3), 37.5 percent anhydrous sodium sulfate (Na2SO4), a 2 percent chlorine bleaching chemical (e.g., sodium dichlor- oisocyanurate with 56 to 64 percent available chlorine), 0.5 percent low- foaming surfactant, and up to 9.5 percent corrosion inhibitors (e.g., aluminum salts). In addition, perborates, clay, perfumes, and color are often added. While chlorine-containing powders may lead to the deterioration of plastic kitchenware, powders without chlorine fail to remove the tannin stains from such beverages as teas. Corrosion inhibitors are added to protect aluminum components (e.g., aluminum saucepans). Machine dish- washing detergents generally contain a maximum of 2 percent surfactant, which consists of a low-foaming, nonionic surfactant (e.g., block copolymers, or propylene oxide and ethylene oxide). Nonionic surfactants are low sudsing and do not ionize in solution; thus, they have no electrical charge. They are also resistant to the chemical effects of hard water and clean well on most soils. For this reason, automatic dishwashing deter- gents produce little to no foaming action. Individual foam films tend to take up and hold particles of soil that have been removed from an item, preventing the soil particles from redepositing on cleaned surfaces. However, if foamy suds were to form within a dishwashing machine in appreciable quantities, rinsing/removal of the foam would cause serious problems and interfere with the washing action of the machine. Automatic dishwashing detergents also suppress natural foam accumulation caused by protein-based soils. Therefore, these detergents are designed not to foam and rely mainly on their strong alkalis and the vigorous action of the machine hardware for cleaning.

Examples of the alkalis included in dishwashing detergent formulations are the carbonate, silicate, or phosphate salts of sodium or potassium (examples noted above), alone or in combination. However, preparations with greater than 5 percent sodium carbonate tend to cause sheet erosion of glassware, which gradually thins glasses and leads to breakage. All of these compounds readily dissolve in water to yield a very high (alkaline/ basic) pH solution. This alkaline environment at high temperatures easily dissolves and disperses greasy food residues. Although dishes can with- stand such basic conditions, human skin (i.e., hands) cannot, so automatic dishwashing detergents are not recommended for use as hand dishwashing detergents. Sodium metasilicate, in particular, is quite caustic and very dangerous if swallowed. In fact, it is children who tend to be poisoned after ingestion of automatic dishwashing detergents from powder- in-door receptacles on the washing machine or directly from the box dispenser. After ingestion, alkalis within the detergent interact with fatty throat tissues and change the fatty tissues into soap, a process called “liquefaction necrosis.” The nature and severity of an associated injury de- pends on the concentration ingested, pH, quantity, physical form (liquid or powder), and duration of exposure.

Liquid formulations have since been introduced as well and often contain a bentonite-based clay substance to prevent the liquid product from seeping out of a standard automatic dishwashing machine powder dispenser.