Sodium tripolyphosphate, also called STPP, or sodium triphosphate, is an inorganic chemical compound, represented as Na5P3O10. It is a white powder and comes in an anhydrous form as well as a hexahydrate form. It has a wide range of applications, but it is majorly used in the detergent industry because it binds strongly to metal as both a bidentate and tridentate chelating agent. Although it is used widely, there are concerns raised in the widespread use of it as a detergent, as it leads to eutrophication.
STPP is produced by heating a stoichiometric mixture of disodium phosphate and monosodium phosphate, under carefully controlled conditions. Through this reaction, 2 million tonnes of STPP is produced annually. The reaction can be written as:
2 Na2HPO4 + NaH2PO4 → Na5P3O10 + 2 H2O
The majority of STPP is consumed as a component of commercial detergents. It serves as a "builder," industrial jargon for a water softener. In hard water (water that contains high concentrations of Mg2+ and Ca2+), detergents are deactivated. Being a highly charged chelating agent, TPP5- binds to di-cations tightly and prevents them from interfering with the sulphonate detergent.
It is used as a coating agent for paper due to its ability to disperse in water and hence it coats the paper white in colour. It also acts as an oil contamination resistance agent and a defending grease agent in paper production. It also acts as a pitch control agent in raw paper pulp in the grinding or washing stages of wood pulp production, by adsorbing the residual resins and other contaminants which impact the productivity of paper mills and the quality of the paper from the wood pulp. It is used as a de-inking process of newsprint.
STPP is a preservative for seafood, meats, poultry, and animal feeds. It is common in food production as E number E451. In foods, STPP is used as an emulsifier and to retain moisture.
STPP is mainly used in commercial detergents to bind to ions in water to prevent detergent from being deactivated. It is used as food preservative, an emulsifier and it also retains moisture in food, such as seafood and meats. It is also used in other products such as ceramics, tanning leather, anticaking agent, flame retardants, textiles, rubber, anticorrosion pigments, fermentation and antifreeze.