Phthalates, also known as phthalate esters, are the dialkyl or alkyl aryl esters of 1,2-benzenedicarboxylic acid. The name phthalate is derived from phthalic acid + -ate. When added to plastics, they allow the long polyvinyl molecules slide against one another. The phthalates are low water solubility, high oil solubility, and low volatility. The polar carboxyl group contributes little to the physical properties of the phthalates, except when R and R' are very small (such as ethyl or methyl groups). They are colourless, odourless liquids produced by reacting phthalic anhydride with an appropriate alcohol (usually 6 to 13 carbon).
About one billion pounds of them are produced each year. They were first produced during the 1920s, and have been produced in large quantities since the 1950s, when PVC was introduced. The most widely used phthalates are di-2-ethyl hexyl phthalate (DEHP), diisodecyl phthalate (DIDP) and diisononyl phthalate (DINP). DEHP is the dominant plasticizer used in PVC, due to its low cost. Benzylbutylphthalate is used in the manufacture of foamed PVC, which is mostly used as a flooring material. Phthalates with small R and R' groups are used as solvents in perfumes and pesticides.
Phthalates are controversial because many phthalates have shown hormonal activity in animal studies. Studies on animals involving large amounts of phthalates have shown damage to the liver, the kidneys, the lungs and the developing testes. Since phthalate molecules are not chemically bound to the polymer, a significant migration is possible. The plastics industry insists that phthalates pose no risk to humans because of the small amounts of phthalates that people are exposed to.
Other uses for phthalates include in nail polish, adhesives, caulk, and paint pigments.