Plasticizers: Types, Uses, Classification, Selection & Regulation

What are Plasticizers?

Plasticizers are relatively non-volatile organic substances (mainly liquids). When incorporated into a plastic or elastomer, they help improve the polymer's:

Flexibility
Extensibility, and
Processability

Plasticizers increase the flow and thermoplasticity of a polymer by decreasing the viscosity of the polymer melt, the glass transition temperature (Tg), the melting temperature (Tm) and the elastic modulus of the finished product without altering the fundamental chemical character of the plasticized material.

Plasticizers are among the most widely used additives in the plastic industry. They are also usually cheaper than other additives used in polymer processing.

Plasticizers are most often used in PVC, the third largest polymer by volume after PP and PE. In turn, PVC is used in a wide range of products. Examples include:

Unplasticized PVC (or rigid PVC) is used in applications such as pipes, siding, and window profiles.
Plasticized PVC (or flexible PVC) finds applications in automotive interior trim, cables, PVC films, flooring, roofing and wall coverings, etc.

Classification of Plasticizers

Plasticizers are commonly classified based on their chemical composition. It is possible to understand the influence of structural elements (e.g. different alcohols in a homologous series of phthalates, adipates, etc.) on the properties of plasticizers and their effect on base polymers.

Different plasticizers affect different physical and chemical properties of materials. Therefore, you need a particular plasticizer to change properties in a certain direction to meet requirements.

There are several general chemical families of plasticizers that are used for polymer modification. Among them, the most commonly used are:

Phthalate Esters – They are produced by esterification of phthalic anhydride or phthalic acid obtained by the oxidation of orthoxylene or naphthalene. Most commonly used phthalate plasticizers include:
1. DEHP: Low molecular weight ortho-phthalate. Still the world’s most widely used PVC plasticizer
2. DINP, DIDP: High molecular weight ortho-phthalates

Aliphatic dibasic acid Esters – These include chemicals such as glutarates, adipates, azelates and sebacates. They are made from aliphatic dibasic acids such as adipic acid and alcohols.

Benzoate Esters – They are esterification products of benzoic acid and selected alcohols or diols.

Trimellitate Esters – They are produced by esterification of trimellitic anhydride (TMA) and typically C8 – C10 alcohols

Polyesters – They are formed by the reaction of many combinations of dicarboxylic acids and difunctional alcohols.

Citrates – They are tetraesters, resulting from the reaction of one mole of citric acid with three moles of alcohol. Citric acid’s lone hydroxyl group is acetylated.

Bio-based Plasticizers – They are based on epoxidized soybean oil (ESBO), epoxidized linseed oil (ELO), castor oil, palm oil, other vegetable oils, starches, sugars etc.

Others – Includes Phosphates, Chlorinated Paraffins, Alkyl Sulfonic Acid Esters and more

When added to polymer, these plasticizers provide several benefits as listed below.

They make a product softer, improve flexibility
The processing becomes possible or easier
Plasticized products do not break easily at cold temperatures

Plasticization Methods & Processing with Plasticizers

There are two main principal methods exist for plasticization - Internal Plasticization and External Plasticization.

Internal Plasticization
A polymer can be internally plasticized by chemically modifying the polymer or monomer so that the flexibility is increased. It involves copolymerization of the monomers of the desired polymer (having high Tg) and that of the plasticizer (having low Tg) so that the plasticizer is an integral part of the polymer chain. The most widely used internal plasticizer monomers are:
- Vinyl acetate
- Vinylidene chloride
But this technique is limited: every copolymer is only suited to certain flexibility requirements

Also, the complexity of the reaction can lead to longer reaction times and increased costs. Internally plasticized materials show temperature dependence and dimensional instability at high temperatures.

External Plasticization
This is the most commonly used method of plasticization because low-cost liquid plasticizers give the formulator freedom in developing formulations for a range of products (from semi-rigid to highly flexible depending on the quantity). The most widely used external plasticizers include esters formed from the reaction of acids or acid anhydrides with alcohols. There are two main groups of external plasticizers:
- A primary plasticizer enhances elongation, softness and flexibility of polymer. They are highly compatible with polymers and can be added in large quantities. For example: up to 50% of vinyl gloves are made up of plasticizers, which make the PVC flexible and soft enough to wear.
- A secondary plasticizer is one that typically cannot be used as the sole plasticizer in a plasticized polymer. Secondary plasticizers may have limited compatibility with the polymer and/or high volatility. They may or may not contain functional groups which allow them to solvate the polymer at processing temperatures. Secondary plasticizers are variously used for:
  - Cost reduction
  - Viscosity reduction
  - Solvency enhancement
  - Surface lubricity augmentation, and
  - Low temperature property improvement
- Extenders are a subset of secondary plasticizers. They are commonly employed with primary plasticizers to reduce costs in general purpose flexible PVC. They are mostly low cost oils having limited compatibility in PVC. They are added to reduce cost and in some cases to improve fire resistance. Examples of extenders include naphthenic hydrocarbons, aliphatic hydrocarbons, chlorinated paraffins (fire resistance) and others.

Processing with Plasticizers

Suspension PVC (S-PVC) process is the common method to manufacture PVC:

PVC obtained in the form of particles with size 50-200 microns
Lower flexible PVC formula costs
PVC particles obtained are mixed with plasticizers & can be extruded in pellets which are further used for processing via extrusion, calendaring, injection molding…
Processing equipment is typically very expensive

Incorporation of an external plasticizer in PVC polymer enhances its flexibility. Addition of plasticizer chiefly involves five distinct steps:

Plasticizer mixed with resin
Plasticizer penetrates and swells the resin particles
Polar groups in the PVC resin are freed from each other
Plasticizer polar groups interact with the polar groups on the PVC chain
PVC structure is re-established Upon cooling, with full retention of plasticizer

Loss of Plasticizers\ Plasticizer Exudation

The incompatibility between polymer and plasticizer can cause exudation. There are several factors which can lead to migration of plasticizer out of plastics surface (or into or onto a substrate to which it is held in intimate contact) like temperature change, humidity change, mechanical stress, weathering, etc.

Loss of plasticizer can lead to less flexibility, embrittlement, and cracking.

All About Phthalate Plasticizers & Current Regulations

Phthalates are typically produced by esterification of phthalic anhydride obtained by the oxidation of orthoxylene.

Dioctyl Terephthalate (DOTP, DEHT) Plasticizer Molecule

Phthalates appear virtually colorless with a faint odor. They have limited solubility in water but are miscible in many of the organic solvents (mineral oil etc.)

Phthalate Plasticizers Benefits & Limitations

Benefits	Limitations
They are the conventional choice as they resist extraction, evaporation and migration Phthalates offer durability, flexibility, weather resistance and are able to withstand high temperatures Phthalates are economical when compared to other plasticizers	In polymers like PVC, phthalates do not bind chemically and leach out of plastics, leading to their occurrence in the environment Some phthalate plasticizers can pose serious risks to health as they are carcinogens and/or developmental toxins Certain phthalates can accumulate at low levels in the human body

Phthalate Plasticizers Applications

Cost: Phthalates which have been used as PVC plasticizers since the earliest days of flexible PVC are both inexpensive and effective. The collapse of oil prices which began in 2015 has further reduced the price of petrochemicals, including phthalate esters. Some phthalate replacements, notably bio-based products, have seen increasing feedstock prices over this time period widening an already present cost differential.

Performance: Certain of the (currently) most widely used phthalate replacement products have processability and permanence limitations.

Supply: The worldwide plasticizer market is quite large, over 7 million tons per year. There’s not yet enough manufacturing capacity to produce those volumes of phthalate replacements.
1. In electrical and electronic applications, phthalate plasticized PVC is used for insulating wires and cables.
2. Phthalate plasticizers are widely used in vinyl based building materials like floorings and wall coverings to provide them with flexibility and durability.

Phthalate Plasticizer Regulations

2001-2006 - DINP and DIDP Are Safe for Use in Current Applications – ECPI Report

The results of the risk assessments for DINP and DIDP, published in April 2006, show that these substances pose no risk to human health or the environment in any of their current applications.

2012 – Australia Risk Assessment Confirms DIDP & DINP Safe for Toys - NICNAS Report

In 2012, the Australian Government Department of Health and Aging found that current exposures to DINP do not indicate a health concern for children, even at the highest exposure levels considered.

Specifically, the report concludes: “Current risk estimates do not indicate a health concern from exposure of children to DINP in toys and child-care articles even at the highest (reasonable worst-case) exposure scenario considered.”

There are currently no restrictions on the use of DINP in toys and child-care articles in Australia.

2013 – EC Confirms Safe Use of DINP and DIDP in all current consumer applications – EC Report

The European Commission (EC) has re-evaluated the restriction on plasticizers DINP (diisononyl phthalate) and DIDP (diisodecyl phthalate). The Commission has concluded that “no unacceptable risk has been characterized for the uses of DINP and DIDP in articles other than toys and childcare articles which can be placed in the mouth”.

The Commission therefore concluded that the existing restriction of DINP and DIDP in toys and childcare articles which can be placed in the mouth should be maintained. The Commission further concluded that “in the light of the absence of any further risks from the uses of DINP and DIDP, the evaluation of potential substitutes has been less pertinent”.

2014 – US CHAP Lifted Ban on DIDP, DNOP and Prohibits >0.1% level of DINP in Child Care Products

U.S. Consumer Product Safety Commission (CPSC) established a Chronic Hazard Advisory Panel (CHAP) to study and review the potential adverse effects of phthalates used in children’s toys and child care articles on children’s health under section 108 of the Consumer Product Safety Improvement Act of 2008:

Three types of phthalates (DEHP, DBP, BBP) are banned permanently in any amount greater than 0.1% in children’s toys and certain child care articles.
Three additional types of phthalates (DINP, DIDP, DNOP) were banned on an interim basis in any amount greater than 0.1%.

CHAP provided its report and recommended the following actions:

Permanent ban on DBP, BBP, and DEHP remain unchanged; Additionally DIBP, DPENP, DHEXP, and DCHP at levels greater than 0.1% to be added to the existing permanently prohibited list
Interim Ban on DINP at levels greater than 0.1% in children’s toys and child care articles to be made permanent
Current bans on DNOP and DIDP be lifted
Use of DIOP on an interim basis until sufficient data are available to determine whether a permanent restriction is necessary
No action on DMP, DEP, and DPHP at this time, but it did encourage appropriate agencies to gather “necessary exposure and hazard data to estimate total exposure to the phthalate alternatives and assess the potential health risks.”

There were also efforts early in the Obama administration to further regulate phthalates under the authority of legislation passed in 1976, the Toxic Substances Control Act (See TSCA sec 5b). However, this was never done.

2017 - Danish EPA Proposal on DINP

Following the fourth re-submission in two years, Danish EPA dossier proposing classification of DINP as a reproductive agent, was accepted by ECHA and the public consultation was initiated in April 2017. Though extensive prior testing, regulatory evaluations, and peer reviewed published scientific reviews the scientific data does not support this classification proposal.

2018 - ECHA RAC Concludes DINP Requires No Classification - ECHA News

ECHA’s Risk Assessment Committee (RAC) has concluded that Di-isononyl phthalate (DINP) does not warrant classification for reprotoxic effects under the EU’s Classification, Labelling and Packaging (CLP) regulation.

RAC undertook a stringent hazard assessment following the rules of the CLP regulation, with the conclusion that, given the lack of evidence of adverse effects, classification is not required. Amongst prior regulatory assessments, the ECHA evaluation of new scientific evidence – endorsed by the European Commission in 2014 – concluded that DINP can be safely used in all current applications. All relevant data are included in the DINP REACH registration dossiers, which were updated in 2015 and 2016.

DEHP - Diethylhexyl Phthalate

Di-2-ethylhexyl-phthalate (DEHP, formula: C₆H₄(C₈H₁₇COO)₂) is a low molecular weight ortho-phthalate produced by esterification of phthalic anhydride with 2-ethyl-hexanol. It is non-volatile, colorless and odorless viscous liquid, soluble in oil, but not in water. Due to its low cost and generally good performance, DEHP is widely employed as a plasticizer in manufacturing articles made of PVC.

Melting point: −50°C
Boiling point: 250 - 257°C at 0.5 kPa

Structure of DEHP

DEHP offers good gelling, satisfactory electrical properties and helps to produce highly elastic compounds with reasonable cold strength. It displays fairly good flexibility at low temperatures and some resistance to high-temperature.

However, DEHP is listed by the IARC as a human carcinogen. DEHP has been implicated as a hormone mimicker and as a developmental toxin in certain studies. In the EU DEHP is considered a SVHC (substance of very high concern) under REACH legislation and cannot be used in most products. It extracts readily into non polar solvents (oils and fats in foods packed in PVC). Therefore the US Food and Drug Administration (FDA) permits use of DEHP-containing packaging only for foods that predominantly consist of water

DEHP is used in applications, such as:

Manufacturing articles made of PVC, copolymers of vinyl chloride and vinyl acetate
Medical devices like catheters, tubings etc.
In developing various formulations ranging from glassy compositions to soft and highly flexible materials
Use is decreasing due to concern about its effects on human health but DEHP is still the most widely used plasticizer in the world

DEHP Replacement

Terephthalate esters, particularly di-2-ethylhexyl terephthalate, are the most popular replacements for DEHP. They are less compatible with PVC but their low cost and long history as commercial plasticizers are their most attractive features.

Dialkyl terephthalates with sidechains containing more than 8 carbon atoms have limited compatibility with PVC. Dialkyl terephthalates in which sidechains contain fewer than 8 carbon atoms have volatility issues. Learn about some benefits and limitations of terephthalate ester in the table below.

Cost	Low
Compatibility with the PVC polymer	Fair
Outdoor weatherability	Fair
Low temperature flexibility	Good
Plasticizer solvency	Fair to Good
Bio-based content	Typically none
Flame retardancy	Poor
High temperature service	Fair
Low plastisol viscosity	Good
Solvent extraction resistance	Poor
Hydrolysis resistance	Fair

DEHP has been progressively deselected for technical reasons such as loss of performance over time, regulation etc. It is progressively substituted by DINP (and DIDP). HMW plasticizers show a particular utility for uses requiring long term performance or durability. Processability, performance, availability and economics have made DINP a “general purpose” phthalate like DEHP and or DIDP. Therefore, DINP appears to be an alternative to most of the uses of DEHP.

Get Inspired: Implement a well-defined methodology to select the right alternatives for phthalates (low-molecular weight) that cater to the stringent health & environmental regulations »

DINP - Diisononyl Phthalate

Diisononyl phthalate (DINP, formula: C₂₆H₄₂O₄) is a high molecular weight ortho-phthalate produced by esterification of phthalic anhydride with isononyl alcohol in a closed system. It is almost colorless and odorless oily liquid. It is very slightly soluble in water but soluble in alcohols, hexane etc. while miscible and compatible with all the monomeric plasticizers used in PVC compounding.

Melting point: −43°C (−45°F; 230 K)
Boiling point: 244-252°C at 0.7 kPa
Flash point: 221°C (c.c.)

Structure of DINP

Diisononyl phthalate offers flexibility and durability to vinyl products - good performance at both low and high temperatures. It is less volatile than DEHP and its good solvency leads to good flexible PVC processing characteristics

DINP plasticizers are employed extensively in indoor and outdoor applications. Being less volatile, it is found effective in applications where products are exposed to relatively high temperatures and need more resistance to degradation. DINP helps the vinyl products withstand many weather conditions, makes them water resistant and provides them high thermal insulation and durability. DINP is combined with PVC powder by the flooring manufacturers to produce soft and flexible finished products.

DIDP - Diisodecyl Phthalate

Diisodecyl phthalate (DIDP, formula: C₂₈H₄₆O₄) is a high molecular weight ortho-phthalate. It is a blend of compounds derived from the esterification of phthalic acid and isomeric decyl alcohols. It is a clear, colorless, and odorless liquid. It is soluble in most organic solvents but insoluble in water. DIDP is widely used in wire and cable formulations and to manufacture automotive interior trims. They are also suitable for coatings for furnishings, cookware, pharmaceutical pills, food wrappers and many other items.

Melting point: −50°C
Boiling point: 250–257°C at 0.5 kPa

Structure of DIDP

DIDP plasticizer increases the flexibility of the plastic/ plastic coating. They are more permanent (less volatile, less water extractable) than DINP. Its good heat stability and electric insulation makes it a preferred choice for heat-resistant electrical cords, car interiors and PVC flooring.

However, the branched alkyl chain structure of DIDP makes it susceptible to oxidation at higher temperatures which may lead to PVC degradation. It has a lower plasticizing efficiency than DOP and needs to be used in higher concentrations to give ideal plasticizing effect

DBP - Dibutyl Phthalate

Dibutyl phthalate (DBP, formula: C₁₆H₂₂O₄) is produced from n-butanol and isobutanol, respectively, which are the co products when 2-ethylhexanol is manufactured. It is colorless to faint yellow in appearance. DBP is typically used in blends with other plasticizers as a solvency booster in flexible PVC compounds which have a low processing temperature requirement.

Melting point: −35°C (−31°F; 238 K)
Boiling point: 340°C (644°F; 613 K)
Flash point: 157 °C (closed cup)

Structure of DBP

However, their low molecular weight makes them too volatile for most of the applications. It was found that the PVC glazing seals used as agricultural films gave off vapors of DBP which were harmful to certain variety of greenhouse crops.

Terephthalate Plasticizers

Terephthalate esters, particularly di-2-ethylhexyl terephthalate, are the most popular replacements for DEHP. Their low cost and long history as commercial plasticizers are their most attractive features.

Dialkyl terephthalates with sidechains containing more than 8 carbon atoms have limited compatibility with PVC.
Dialkyl terephthalates in which sidechains contain fewer than 8 carbon atoms have volatility issues.

Mentioned in the below table are some benefits of terephthalate plasticizers.

Cost	Low
Compatibility with the PVC polymer	Fair
Outdoor weatherability	Fair
Low temperature flexibility	Good
Plasticizer solvency	Fair to Good
Bio-based content	None
Flame retardancy	Poor
High temperature service	Fair
Low plastisol viscosity	Good
Solvent extraction resistance	Poor
Hydrolysis resistance	Fair

Other Phthalate Plasticizers

Note that isoalkyl phthalates (e.g., DIOP, DIUP, DTDP) do not have a methyl branch on the penultimate carbon of the alkyl chain. For alkyl groups containing 6 or more carbons the “iso” prefix, by convention, simply means “branched”.

See structures in the following table.

Other Phthalate Plasticizers Used in Polymers

Butyl Benzyl Phthalate (C₁₉H₂₀O₄)

MP: -35°C (-31°F; 238 K)
BP: 370°C (698°F; 643 K)

It is an ester of phthalic acid, benzyl alcohol and n-butanol. This phthalate is frequently used as a plasticizer for vinyl foams, which are often used as vinyl floor coverings/ tiles and in the automotive industry.

Diisoheptyl phthalate (DIHP, C₂₂H₃₄O₄)

MP: -35°C (-31°F; 238 K)
BP: 370°C (698°F; 643 K)

Diisoheptyl phthalate consists of chemical compounds containing various isoheptyl esters of phthalic acid.

Dihexyl phthalate (DHP, C₆H₄(COOC₆H₁₃)₂)

MP: -28 to -27°C
BP: 350°C

Alkyl sidechains may contain some branching

Diisooctyl phthalate(DIOP, C₂₄H₃₈O₄)

MP: -28 to -27°C
BP: 350°C

It is a clear oily liquid with a slight odor and is denser and partially soluble in water. It is obtained by reaction of phthalic anhydride with iso- octanol in the presence of an acid catalyst.

Di-iso-undecyl phthalate (DIUP)

MP: -28 to -27°C
BP: 350°C

DIUP is a high molecular weight phthalate. Being nonvolatile, it is widely employed for high temperature applications like insulating heat resistant cables. DIUP is less susceptible to fogging than DEHP

Dimethyl phthalate (DMP, C₁₀H₁₀O₄)

MP: 2°C (36°F; 275 K)
BP: 283 to 284°C

DMP is a dimethyl ester of 1,2- benzenedicarboxylic acid. It is a colorless liquid with a slight aromatic odor

Diisotridecyl phthalate (DTDP, C₃₄H₅₈O₄)

MP: -28 to -27°C
BP: 350°C

DTDP is the highest weight dialkyl phthalate to be used as a plasticizer. It was widely used as a high temperature plasticizer for PVC until trimellitates came into existence. It needs high processing temperatures for compounding with PVC.

Alternative Plasticizers

The choice of the phthalate replacement or alternative plasticizers (if any) is usually based on several criteria. These include:

Cost
Expected exposure conditions of finished product during its service life. These include compatibility, outdoor weatherability, low temperature flexibility etc.
Processing condition limitations like low processing temperatures or high processing rates

The type of plasticizers which can be used to overcome these issues are listed below.

Safer Plasticizers to Overcome Performance Issues

Cost – Ring saturated phthalates, DOTP, certain vegetable oil derivatives (e.g. ESBO)

Compatibility - Benzoates/dibenzoates, Alkyl sulfonic acid esters, Trimellitates

Outdoor weatherability – Trimellitates, Alkyl sulfonic acid esters (depending on severity of expected service life)

Low temperature flexibility - Esters of aliphatic dibasic acids, some vegetable oil derivatives (e.g. acetylated monoglyceride esters, monoesters of fatty acids)

Plasticizer solvency - Benzoates/dibenzoates, some vegetable oil derivatives (e.g. acetylated monoglyceride esters, monoesters of fatty acids), TXIB

Flame retardancy - Phosphate esters (only)

High temperature service – Trimellitates, some vegetable oil derivatives (e.g. see Dow Ecolibrium products)

Low plastisol viscosity - Benzoate esters (not dibenzoates), TXIB, esters of aliphatic dibasic acids

Solvent extraction resistance - Polyesters

Hydrolysis resistance - Alkyl sulfonic acid esters

Adipate Plasticizers

In PVC applications, adipates offer enhanced low temperature properties as compared to phthalates of similar alkyl chain length.

Polymeric plasticizers (typically made from aliphatic dibasic acids such as adipic acid and diols) are valued primarily for their permanence. These plasticizers are generally classified as polyesters, not adipates. Many have low solvency for PVC and high viscosity, both of which can make processing f-PVC compounds difficult. Many have poor low temperature properties and may be sensitive to moisture.

Check out the table below for benefits of polymeric plasticizers.

Cost	Moderately High
Compatibility with the PVC polymer	Fair to Good
Outdoor weatherability	Fair to poor
Low temperature flexibility	Good
Plasticizer solvency	Fair
Bio-based content	None
Flame retardancy	Poor
High temperature service	Fair to poor
Low plastisol viscosity	Good
Solvent extraction resistance	Fair to good
Hydrolysis resistance	Fair

Adipate plasticizers are more volatile, exhibit poorer fusion and compatibility with PVC i.e. they possess higher migration rates. They are expensive relative to some other alternative plasticizers. Generally used in blends with higher phthalates to deliver optimum plasticizing properties.

Benzoate Plasticizers

Benzoate and dibenzoate esters are both highly solvating plasticizers for PVC. Because of their high volatility, monobenzoates are typically used only as solvency boosting or viscosity depressing additives in flexible PVC. Dibenzoate plasticizers are valued primarily for their strong solvency, but they are defensive to phthalate plasticizer in low temperature properties and plastisol viscosity characteristics. Both benzoate and dibenzoate plasticizers are often used in blends with other plasticizers.

Some common benefits and limitations of benzoate/dibenzoate esters can be found in the table below.

Cost	Moderate
Compatibility with the PVC polymer	Good
Outdoor weatherability	Poor to Good
Low temperature flexibility	Poor to Good
Plasticizer solvency	Excellent
Bio-based content	Typically none
Flame retardancy	Poor
Low plastisol viscosity	Poor to good
Solvent extraction resistance	Poor to fair
Hydrolysis resistance	Fair

Benzoates also act as processing aids. They display good UV stability, excellent stain resistance, good oil extraction resistance as well as high solvating power. Low molecular weight give these plasticizers processing advantages by lowering the processing temperatures.

However, benzoates are highly volatile in nature. There are many unique chemistries with differentiated performance. Dibenzoates have a reduced low temperature flexibility and can give poor plastisol flow properties.

Benzoates offer optimum performance in PVC and other thermoplastic polymers. Many applications use benzoates as part of a plasticizer blend to diminish the challenges faced during processing. Benzoates (especially dibenzoates) are used in some flexible PVC flooring (resilient flooring).

Citrate Plasticizers

Citrate esters are used in many f-PVC toys. They are valued because they are “natural” products which may have high bio-based content (depending on how they are made) and they have low toxicity. Some typical features of citrates are mentioned in the table below.

Cost	High
Compatibility with the PVC polymer	Fair
Outdoor weatherability	Fair to poor
Low temperature flexibility	Fair to Good
Plasticizer solvency	Fair
Bio-based content	None to High
Flame retardancy	Poor
High temperature service	Poor to Fair
Low plastisol viscosity	Poor to Fair
Solvent extraction resistance	Fair
Hydrolysis resistance	Poor to Fair

Citric acid esters/ citrates have some direct food additive clearances as well as indirect clearances in PVC. These offer good performance and excellent flexibility at low temperatures. They provide good heat and light stability. Citric acid esters can be partially bio-based, are non-toxic and are accepted by FDA for use in food-contact applications.

However, citrate Plasticizers are highly volatile and a significant amount is lost due to this property. Citrates lack permanency and therefore, are not employed in resilient applications like cables, flooring or roofing. They induce more fogging in film applications.

Citrates/ Citric acid esters are used to plasticize vinyl resins in toys, medical devices and pacifiers for infants. Being FDA approved, citrates find uses in food packaging film applications and pharmaceutical preparations. Citrates are compatible with polymers like PVC, PVA, PVB, polypropylene. Esters of citric acid are also used as foam inhibitors

Trimellitate Plasticizers

Trimellitic anhydride (TMA) is a tri-carboxylic acid of similar structure to phthalic anhydride or acid.

Trimellitate esters are used primarily because of their low volatility and high permanence. Commercial trimellitic anhydride (a starting material for trimellitate manufacture) typically contains very small amount of phthalic anhydride so, strictly speaking, trimellitate plasticizers often are not “phthalate alternative”.

Mentioned in the below table are some benefits of these plasticizers.

Cost	Moderately High
Compatibility with the PVC polymer	Good
Outdoor weatherability	Fair to Good
Low temperature flexibility	Fair to Good
Plasticizer solvency	Fair
Bio-based content	Typically none
Flame retardancy	Poor
High temperature service	Excellent
Low plastisol viscosity	Poor
Solvent extraction resistance	Fair
Hydrolysis resistance	Fair

Trimellitate plasticizers have a lower volatility, better extraction resistance and good processability when compared to phthalates. Trimellitates cannot be judged as phthalate free plasticizers as traces of phthalates have been found in them.

Trimellitates are employed in PVC compounds like high temperature rated wire insulation, gaskets and some parts for automobile interiors.

Other Plasticizers Used in Plasticizers

Phosphates

Phosphate ester plasticizers are used primarily to impart flame retardancy to f-PVC. Some phosphate plasticizers are also used to improve f-PVC compounds’ resistance to UV light (outdoor weatherability). They are not typically used as primary plasticizers for PVC.

Cost	High
Compatibility with the PVC polymer	Good
Outdoor weatherability	Fair to Good
Low temperature flexibility	Poor to Fair
Plasticizer solvency	Good
Bio-based content	None
Flame retardancy	Good
High temperature service	Fair
Low plastisol viscosity	Good
Solvent extraction resistance	Poor
Hydrolysis resistance	Fair

Triaryl and alkyl diaryl phosphates are the most important category of flame retardant phosphate plasticizers used with PVC, specifically to achieve flame retardancy and/or low smoke generation. Phosphates are primary plasticizers for PVC and can be utilized as sole plasticizers or in a cost optimized blend.

Triaryl phosphates show excellent flame retardancy with low volatility; however they have poorer low-temperature flexibility. Alkyl diaryl phosphate esters have good low-temperature flexibility but are more volatile and offer poorer flame retardancy than the triaryl esters. Commonly restricted to applications requiring enhanced flame and smoke performance, some phosphates have cited approval in food and medical device regulations.

Chlorinated Paraffins

Chlorinated paraffins are obtained by the chlorination of hydrocarbons and consist of 30-70% chlorine. They have low volatility and act as a flame retardant due to the presence of chlorine.

Chlorinated paraffins offer high chemical stability and moisture resistance but are thermally unstable, which limits their applications to processing temperatures within 175⁰C. Therefore, for higher processing temperatures, addition of other stabilizers is required. It is known that higher the chlorine content, weaker is the plasticizing effect of chlorinated paraffins for PVC.

Ring Saturated Variants of Phthalate Esters (e.g. DINCH)

Plasticizers like DINCH (di-isononyl ester of cyclohexane-1,2-dioc acid) are valued as phthalate look alikes without (proven) adverse effects on human health. They have relatively low solvating strength for PVC and compatibility with PVC is defensive to that of their phthalate analogs. Higher MW versions of ring saturated dialkyl phthalates are increasingly incompatible with PVC.

Cost	Moderate
Compatibility with the PVC polymer	Fair
Outdoor weatherability	Fair
Low temperature flexibility	Good
Plasticizer solvency	Fair
Bio-based content	None
Flame retardancy	Poor
High temperature service	Poor
Low plastisol viscosity	Good
Solvent extraction resistance	Poor
Hydrolysis resistance	Fair

Alkyl Sulfonic Acid Esters

Alkyl sulfonic acid esters are valued for their chemical resistance, especially their resistance to hydrolysis. They are promoted as general purpose plasticizers. There are relatively few manufacturers of these products.

Cost	Moderate
Compatibility with the PVC polymer	Good
Outdoor weatherability	Good
Low temperature flexibility	Fair
Plasticizer solvency	Good
Bio-based content	Typically None
Flame retardancy	Poor
High temperature service	Fair (DEHP like)
Low plastisol viscosity	Good
Solvent extraction resistance	Poor
Hydrolysis resistance	Good

Aliphatic Dibasic Acid Esters

Aliphatic dibasic acid esters are used primarily for the good low temperature properties which they impart to flexible PVC compounds. They are very efficient plasticizers and many are effective plastisol viscosity depressants. Some may have bio-based content. Drawbacks are their relatively poor compatibility with PVC and relatively low solvating strength.

Cost	Moderate
Compatibility with the PVC polymer	Fair
Outdoor weatherability	Poor to Fair
Low temperature flexibility	Excellent
Plasticizer solvency	Fair
Bio-based content	Typically None
Flame retardancy	Poor
High temperature service	Poor
Low plastisol viscosity	Excellent
Solvent extraction resistance	Poor
Hydrolysis resistance	Fair

Polyol-Carboxylic Acid Esters

Cost	Moderately High
Compatibility with the PVC polymer	Good
Low temperature flexibility	Good
Plasticizer solvency	Good
Flame retardancy	Poor
High temperature service	Fair to Good
Low plastisol viscosity	Fair to Poor
Solvent extraction resistance	Poor

Polymeric Plasticizers

Polymeric plasticizers (typically made from aliphatic dibasic acids such as adipic acid and diols) are valued primarily for their permanence. Many have low solvency for PVC and high viscosity, both of which can make processing f-PVC compounds difficult. Many have poor low temperature properties and may be sensitive to moisture.

Cost	High
Compatibility with the PVC polymer	Good
Outdoor weatherability	Fair to Poor
Low temperature flexibility	Fair to Poor
Plasticizer solvency	Fair
Bio-based content	Typically None
Flame retardancy	Poor
High temperature service	Fair to Good
Low plastisol viscosity	Poor
Solvent extraction resistance	Fair to Good
Hydrolysis resistance	Fair to Good

Other Aliphatic Esters of Dibasic Acids

In this category, di-2-ethylhexyl sebacate (DOS), di-2-ethylhexyl azelate (DOZ) and di-isodecyl sebacate (DIDS) are the most commonly used plasticizers. When compared to adipates these plasticizers impart superior low temperature performances and their use is limited to applications that require extremely low temperature flexibility. Like adipates, they have limited compatibility with PVC.

Biobased Plasticizers

As part of the shift to sustainable ingredients, bio-based plasticizers continue to gain further importance. Being bio-based, they offer the dual advantage of being phthalate alternative along with lowering our dependence on fossil fuel based feedstock. The common feedstock for this class of plasticizers is mentioned below.

As the name says, biobased plasticizers are majorly based on:

Epoxidized soybean oil (ESBO)
Epoxidized linseed oil (ELO)
Castor oil
Palm oil
Other Vegetable oils
Starches
Sugars (including isosorbide esters)
others

There are few more plasticizers as well that are based on renewably sourced isosorbides and alkanoic acids. Isosorbide diesters are a non-toxic alternative to phthalates and offer promising properties for PVC.

Being naturally/renewable sourced, bio-based plasticizers are sometimes easily approved for food contact and medical applications. This category of plasticizers can be easily incorporated in toys and teething products for infants. Some of them have also found use in wire insulation & jacketing, household & consumer goods, flooring, carpet backing, and other building & construction end use applications.

Below mentioned are benefits of vegetable oil derivatives – epoxides. Chemically, epoxy plasticizers are esters which contain one or more epoxidized double bonds. Examples include epoxidized soybean oil (ESBO) and epoxidized linseed oil (ELO). Oxidation of an olefinic double bond to an oxirane structure leads to the formation of epoxy groups. The presence of an epoxy group helps these plasticizers to improve heat stability of the manufactured PVC articles. At higher concentrations epoxy plasticizers sometimes develop incompatibility with PVC.

Cost	Moderate to very high
Compatibility with the PVC polymer	Fair to Good
Outdoor weatherability	Fair
Low temperature flexibility	Poor (triglyceride esters of fatty acids) to good
Plasticizer solvency	Poor (triglyceride esters of fatty acids) to good
Bio-based content	Typically high
Flame retardancy	Poor
High temperature service	Good (triglycerides)
Low plastisol viscosity	Poor (triglycleride esters) to good
Solvent extraction resistance	Poor
Hydrolysis resistance	Fair

Vegetable oil derivatives are the most widely used natural product type plasticizers. Products consisting of triglyceride esters of unsaturated fatty acids (e.g. soybean oil, linseed oil) in which the double bonds in the fatty acid residues have typically been epoxidized have been commercial products for decades.

Drawbacks include:

Low solvating strength
High viscosities, and
Poor low temperature properties

Other vegetable oil derivatives (e.g. monoesters made from vegetable oil derived fatty acids or acetylated monoglycerides derived from vegetable oils) may have better solvency, compatibility and low temperature properties but can have high volatility. Note that there are many types of vegetable oil derivatives which are used as plasticizers.

Selection of Plasticizers

While selecting a general-purpose plasticizer for PVC, the main attributes to be checked are listed below.

Regulatory clearance – Safe for use and Safe in use
Good compatibility
Cost effective
UV resistant
Long service life and sustainable-favorable LCA
High permanency thermally stable

Among them, regulation is an important decision factor while selecting plasticizers.

Phthalates in Child Care Products

In recent years, there have been a lot of discussion on phthalate plasticizers. But in fact, not all phthalates are prohibited.

For example, in neither the US (federal and state legislation) nor the EU is the use of all phthalate plasticizers specifically prohibited in any plasticized PVC product.

We have already discussed recent regulatory status w.r.t phthalate plasticizers in child care articles.

There are also federal regulations (not laws) for plasticizers used in food contact applications and in medical devices:

Only certain plasticizers are preapproved by the Food and Drug Administration for use in flexible PVC products used in various food contact applications (See USFDA Code of Federal Regulations Title 21, Part 177, Indirect Food Additives – Polymers)
Likewise, flexible PVC medical devices may (and often do) contain phthalate plasticizers (flexible PVC I.V. tubing, blood bags and examination gloves most often contain DEHP) if the finished product meets certification requirements

California Proposition 65 listed

On a state level, certain phthalate plasticizers are California Proposition 65 listed. This listing means that a chemical “is known by the State of California to cause cancer, birth defects or reproductive harm”. It does not prohibit the use of the listed chemical or items containing the chemical in the State of California nor does it necessarily create a labeling requirement for items containing the Proposition 65 listed chemical.

If it can be demonstrated that a flexible PVC product containing (Proposition 65 listed) DEHP plasticizer, for example, cannot expose a consumer to more than the maximum acceptable daily limit of DEHP (established by the state of California), no labeling is required in California.

Plasticizers in Europe

In the EU, there is a more systematic approach to chemical regulation. Under the REACH protocol for evaluating chemicals used in commerce, certain phthalates (including DEHP, the world’s most widely used plasticizer) have been effectively banned from manufacture, importation and use in the EU. Certain other high-volume phthalates including DINP and DIDP have been fully approved for use in all their current applications.

Plasticizers Regulatory Status
Source: ExxonMobil
(Click on Image to Enlarge)

Plasticizers for Plastics and Elastomers

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Selecting Plasticizers for Polymers