Phthalates ( THAL-ates "phthalate" in Collins English Dictionary), or phthalate esters, are esters of phthalic acid. They are colorless, odorless, oily compounds, although commercial samples can be yellowish with faint odors. Being fairly chemically inert and easily produced, they are widely used as plasticizers, i.e., substances added to polymers to increase their flexibility, transparency, durability, and longevity. They are used primarily to soften polyvinyl chloride (PVC). While phthalates are commonly used as plasticizers, not all plasticizers are phthalates. The two terms are specific, unique, and not used interchangeably.
The use of phthalate plasticizers has had a profound effect on the commercialization of PVC, promoting its use for major industrial and consumer applications where flexibility is required, such as for tubing, siding, packaging and wire sheathing.
Phthalates are controversial because, when ingested, they pose a threat as endocrine disruptors. Consequently their use is regulated, e.g. in the United States, Canada, and European Union.
Production Phthalate esters are produced industrially by the reaction of phthalic anhydride with excess alcohol. The monoesterification occurs readily, but the second step is slow:
The conversion is conducted at high temperatures to drive off the water. Typical catalysts are tin or titanium alkoxides or carboxylates.
The properties of the phthalate are affected somewhat by the alcohol. Around 30 are, or have been, commercially important. Phthalates' share of the global plasticisers market has been decreasing since around 2000, but total production has been increasing, with around 5.5 million tonnes made in 2015, up from around 2.7 million tonnes in the 1980s. This increase is due to the increasing size of the plasticiser market, largely due to increases in PVC production, which nearly doubled between 2000 and 2020. The People's Republic of China is the largest consumer of phthalates, accounting for around 45% of all use. Europe and the United States together account for around 25% of use, with the remainder widely spread around the world.
+ Common phthalates Ordered by molecular weight, commercially important compounds shown in bold Name Abbreviation Alcohol carbon numberMolecular weight (g/mol)CAS No. Properties of concern for human health (ECHA classification 2022) Dimethyl phthalate DMP 1 194.18 131-11-3 Diethyl phthalate DEP 2 222.24 84-66-2 Under assessment as endocrine disrupting Diallyl phthalate DAP 3 246.26 131-17-9 Skin sensitising Di-n-propyl phthalate DPP 3 250.29 131-16-8 Di-n-butyl phthalate DBP 4 278.34 84-74-2 Toxic to reproduction, endocrine disrupting. Diisobutyl phthalate DIBP 4 278.34 84-69-5 Toxic to reproduction, endocrine disrupting Di-2-methoxyethyl phthalate DMEP 3 282.29 117-82-8 Toxic to reproduction Butyl cyclohexyl phthalate BCP 4 – 6 304.38 84-64-0 Di-n-pentyl phthalate DNPP 5 306.4 131-18-0 Toxic to reproduction Dicyclohexyl phthalate DCP 6 330.42 84-61-7 Toxic to reproduction, endocrine disrupting, skin sensitising Butyl benzyl phthalate BBP 4 – 7 312.36 85-68-7 Toxic to reproduction, endocrine disrupting Di-n-hexyl phthalate DNHP 6 334.45 84-75-3 Toxic to reproduction Diisohexyl phthalate DIHxP 6 334.45 146-50-9 Toxic to reproduction Diisoheptyl phthalate DIHpP 7 362.5 41451-28-9 Toxic to reproduction Butyl decyl phthalate BDP 4 – 10 362.5 89-19-0 Dibutoxy ethyl phthalate DBEP 6 366.45 117-83-9 Di(2-ethylhexyl) phthalate DEHP, DOP 8 390.56 117-81-7 Toxic to reproduction, endocrine disrupting Di(n-octyl) phthalate DNOP 8 390.56 117-84-0 Not classified but some uses restricted Diisooctyl phthalate DIOP 8 390.56 27554-26-3 Toxic to reproduction n-Octyl n-decyl phthalate ODP 8 – 10 418.61 119-07-3 Diisononyl phthalate DINP 9 418.61 28553-12-0 Not classified but some uses restricted Di(2-propylheptyl) phthalate DPHP 10 446.66 53306-54-0 Under assessment as endocrine disrupting Diisodecyl phthalate DIDP 10 446.66 26761-40-0 Diundecyl phthalate DUP 11 474.72 3648-20-2 Diisoundecyl phthalate DIUP 11 474.72 85507-79-5 Ditridecyl phthalate DTDP 13 530.82 119-06-2 Diisotridecyl phthalate DITP 13 530.82 68515-47-9
Uses PVC plasticisers
Between 90 and 95% of all phthalates are used as plasticisers for the production of flexible PVC. The majority is used in films and cable sheathing. Flexible PVC can consist of over 85% plasticizer by mass, however unplasticized PVC (UPVC) should not contain any. Pthalates were the first commercially important compounds for this role, a historic advantage that has led to them becoming firmly embedded in flexible PVC technology. Among the common plastics, PVC is unique in its acceptance of large amounts of plasticizer with gradual changes in physical properties from a rigid solid to a soft gel. Phthalates derived from alcohols with 7–13 carbon atoms occupy a privileged position as general purpose plasticizers, suitable for almost all flexible PVC applications. Phthalates larger than this have limited compatibility in PVC, with di(isotridecyl) phthalate representing the practical upper limit. Conversely, plasticizers derived from alcohols with 4–6 carbon atoms are too volatile to be used on their own, but have been used alongside other compounds as secondary plasticizers, where they improve low-temperature flexibility. Compounds derived from alcohols with 1–3 carbon atoms are not used as plasticizers in PVC at all, due to excessive fuming at processing temperatures (typically 180–210 °C).
Historically DINP, DEHP, BBP, DBP, and DIHP have been the most important phthalates, however many of these are now facing regulatory pressure and gradual phase-outs. Almost all phthalates derived from alcohols with between 3 and 8 carbons are classed as toxic by ECHA. This includes bis(2-ethylhexyl) phthalate (DEHP or DOP), which has long been the most widely used phthalate, with commercial production beginning in the 1930s. In the EU, the use of DEHP is restricted under REACH and it can only be used in specific cases if an authorisation has been granted; similar restrictions exist in many other jurisdictions. Despite this, the phase-out of DEHP is slow and it was still the most frequently used plasticizer in 2018, with an estimated global production of 3.24 million tonnes. DINP and DIDP are used as a substitutes for DEHP in many applications, as they are not classified as hazardous. Non-phthalate plasticizers are also being increasingly used.
+ PVC properties as a function of phthalate plasticizer level Plasticizer content (% DINP by weight) Specific gravity (20 °C) Shore hardness (type A, 15 s) Flexural stiffness (Mpa) Tensile strength (Mpa) Elongation at break (%) Example applications Rigid 0 1.4 900 41 <15 Unplasticized PVC (UPVC): window frames and sills, doors, rigid pipe Semi-rigid 25 1.26 94 69 31 225 Vinyl flooring, flexible pipe, thin films (stretch wrap), advertising banners Flexible 33 1.22 84 12 21 295 Wire and cable insulation, flexible pipe Very flexible 44 1.17 66 3.4 14 400 Boots and clothing, inflatables, Extremely flexible 86 1.02 < 10 Fishing lures (soft plastic bait), polymer clay, plastisol inks
Non-PVC plasticisers Phthalates see use as plasticisers in various other polymers, with applications centred around coatings such as lacquers, varnishes, and paints. The addition of phthalates imparts some flexibility to these materials, reducing their tendency to chip. Phthalates derived from alcohols with between 1–4 carbon atoms are used as plasticisers for cellulose-type plastics, such as cellulose acetate, nitrocellulose and cellulose acetate butyrate, with commonly encountered applications including nail polish. Most phthalates are also compatible with alkyds and acrylic resins, which are used in both oil and emulsion based paints.
Other plasticised polymer systems include polyvinyl butyral (particularly the forms used to make laminated glass), PVA and its co-polymers like PVCA. They are also compatible in nylon, polystyrene, polyurethanes, and certain rubbers; but their use in these is very limited.
Phthalates can plasticise ethyl cellulose, polyvinyl acetate phthalate (PVAP) and cellulose acetate phthalate (CAP), all of which are used to make enteric coatings for tablet and capsule medications. These coatings protect drugs from the acidity of the stomach, but allow their release and absorption in the intestines.
Solvent and phlegmatizer Phthalate esters are widely used as solvents for highly reactive organic peroxides. Thousands of tonnes are consumed annually for this purpose. The great advantage offered by these esters is that they are phlegmatizers, i.e. they minimize the explosive tendencies of a family of chemical compounds that otherwise are potentially dangerous to handle. Phthalates have also been used for producing plastic explosives such as Semtex.
Other uses Relatively minor amounts of some phthalates find use in personal-care items such as eye shadow, moisturizer, nail polish, liquid soap, and hair spray.Peter M. Lorz, Friedrich K. Towae, Walter Enke, Rudolf Jäckh, Naresh Bhargava, Wolfgang Hillesheim "Phthalic Acid and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2007, Wiley-VCH, Weinheim. Low-molecular-weight phthalates like dimethyl phthalate and diethyl phthalate are used as fixatives for perfumes. Dimethyl phthalate has been also used as an insect repellent and is especially useful against ixodid ticks responsible for Lyme disease. and species of mosquitoes such as Anopheles stephensi, Culex pipiens and Aedes aegypti,
Diallyl phthalate is used to prepare vinyl ester resins with good electrical insulation properties. These resins are used to manufacture of electronics components.
Properties Phthalates are colorless, odorless liquids produced by the reaction of phthalic anhydride with alcohols. From the chemical perspective, they are both lipophilic and somewhat polar. This combination allows them to serve as a plasticizer (softener) for PVC, when the two are blended together. Because they are not chemically bonded to the host plastics, phthalates are released from the article by relatively gentle means. For example, they can be extracted by contact with skin.
Alternatives
Being inexpensive, nontoxic (in an acute sense), colorless, noncorrosive, biodegradable, and with easily tuned physical properties, phthalate esters are nearly ideal plasticizers. Among the numerous alternative plasticizers are dioctyl terephthalate (DEHT) (a terephthalate isomeric with DEHP) and 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) (a hydrogenated version of DINP). Both DEHT and DINCH have been used in high volumes for a variety of products used in contact with humans as alternative plasticizers for DEHP and DINP. Some of these products include medical devices, toys, and food packaging. DEHT and DINCH are more hydrophobic than other phthalate alternatives such as bis(2-ethylhexyl) adipate (DEHA) and diisodecyl adipate (DIDA). Since alternative plasticizers such as DEHT and DINCH are more likely to bind to organic matter and airborne particles indoors, exposure occurs primarily through food consumption and contact with dust.
Many bio-based plasticizers based on vegetable oil have been developed.
Occurrence and exposure Human exposure