Phthalates

Phthalates, or phthalate esters, are esters of phthalic acid. They are mainly used as plasticizers, i.e., substances added to plastics to increase their flexibility, transparency, durability, and longevity. They are used primarily to soften polyvinyl chloride. While phthalates are commonly used as plasticizers, not all plasticizers are phthalates. The two terms are specific, unique, and not used interchangeably.
Lower-molecular-weight phthalates are typically replaced in many products in the United States, Canada, and European Union over health concerns. They are being replaced by higher molecular-weight phthalates as well as non-phthalic plasticizers.
Phthalates are commonly ingested in small quantities via the diet. One of the most commonly known phthalates is bis phthalate. In many countries DEHP is regulated as a toxin, and is banned from use in broad categories of consumer goods, such as cosmetics, children's toys, medical devices, and food packaging.
There are numerous forms of phthalates not regulated by governments.

Production

Phthalate esters are produced industrially by the reaction of phthalic anhydride with excess alcohol. Often the phthalic anhydride is molten. 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 based on tin or titanium alkoxides or carboxylates.
The properties of the phthalate can be varied by changing the alcohol. Around 30 are, or have been, commercially important. Phthalates' share of the global plasticisers market has been decreasing since around 2000 however total production has been increasing, with around 5.5 million tonnes made in 2015, up from around 2.7 million tonnes in the 1980s. The explanation for this is the increasing size of the plasticiser market, largely due driven by increases in PVC production, which nearly doubled between 2000 and 2020. The People's Republic of China is the largest consumer, 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.

Name	Abbreviation	Alcohol carbon number	Molecular weight	CAS No.	Properties of concern for human health
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 phthalate	DEHP, DOP	8	390.56	117-81-7	Toxic to reproduction, endocrine disrupting
Di 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 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 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 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.
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 phthalate, 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.

	Plasticizer content	Specific gravity	Shore hardness	Flexural stiffness	Tensile strength	Elongation at break	Example applications
Rigid	0	1.4		900	41	<15	Unplasticized PVC : window frames and sills, doors, rigid pipe
Semi-rigid	25	1.26	94	69	31	225	Vinyl flooring, flexible pipe, thin films, 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, 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, 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 and cellulose acetate phthalate, 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.