Chemistry

What are plasticisers?

Plasticisers are substances added to plastic during manufacturing to enhance its flexibility, durability, and other mechanical properties. They function by increasing the movement of polymer chains within the plastic material, which lowers intermolecular forces and allows the chains to glide past each other more efficiently. This leads to a more adaptable and pliable plastic product.

The chemical makeup of plasticisers differs depending on the type of polymer and plasticiser used and can be classified into various categories based on their chemical structure:

Phthalate Plasticisers

Phthalates, more specifically ortho-phthalates, are one of the most widely used types of plasticisers. These are esters of ortho-phthalic acid and alcohols. Phthalate plasticisers are added to polymers like polyvinyl chloride (PVC) to increase their flexibility. Common phthalate plasticisers include di(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP) and di(2-propylheptyl) phthalate (DPHP).

Terephthalates Plasticisers

Terephthalates differ structurally from phthalates which are benzene-1,2-dicarboxylic acid esters. Terephthalates are benzene-1,4-dicarboxylic acid esters with alcohols. Di(2-ethylhexyl) terephthalate (DEHT) is the most commonly used representative of this chemical class, but there is also a di(isopentyl) terephthalate (DPT).

Cyclohexanoate Plasticisers

Cyclohexane-1,2-dicarboxylic acid, diisononyl ester (DINCH) is the most prominent plasticiser know in this chemical class, there is also cyclohexane-1,2-dicarboxylic acid, (2-ethylhexyl) ester (DEHCH) and ring hydrogenated terephthalates, which are also no more aromatic. Representatives are Cyclohexane-1, .4, dicarboxylic acid, (2-ethylhexyl) ester (DEH14CH) and Cyclohexane-1,4- dicarboxylic acid, diisononyl ester (DINCD).

Trimellitate Plasticisers

Trimellitate plasticisers are based on trimellitic acid and are often used when high-temperature stability is required. They are used in applications like wire and cable insulation. Examples are Tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate (TEHTM, also referred to as trioctyl trimellitate (TOTM) and Tris(isononyl) benzene-1,2,4-tricarboxylate (TINTM).

Adipate Plasticisers

These plasticisers are derived from 1,6-hexanedioic acid, also referred to as adipic acid. They are often used in applications that require low-temperature flexibility and resistance to oil and water. Examples include di(2-ethylhexyl) adipate (DEHA) (synonym: dioctyl adipate (DOA) and diisononyl adipate (DINA).

Sebacate and Azelate Plasticisers

Sebacates, esters of sebacic acid are di (2-ethylhexyl-, also referred to as dioctyl sebacate (DOS) and di(isodecyl) sebacate (DIDS). Sebacic acid is 1, 10-decanedioic acid. Diisodecylazelate is 1,9- Nonanedioic acid is (DDZ) Azelaic acid esters are also used as plasticisers, an example is diisodecyl azelate (DIDA).

Epoxide Plasticisers

These plasticisers contain epoxy functional groups. They are used to improve the heat and light stability of polymers. Epoxidised soybean oil (ESBO) is a common example.

Polymeric Plasticisers

These are large molecules that are chemically similar to the polymer matrix. Polymeric adipates based on different further monomers are often used to improve the mechanical properties of the plastic without migrating to the surface. Polymeric plasticisers can also enhance the compatibility between different polymers in blends.

The chemistry of plasticisers involves their interactions with the polymer chains. The plasticiser molecules insert themselves between the polymer chains, reducing the intermolecular forces (such as van der Waals forces) that hold the chains together. This allows the polymer chains to move more freely, making the plastic material softer and more flexible.

Overall, the chemistry behind plasticisers is a complex and diverse field that involves the interactions between various chemical compounds and polymer structures to achieve desired material properties.

Table with all the types of plasticisers

 

The chemistry of plasticisers

The chemistry of plasticisers involves their interactions with the polymer chains. The plasticiser molecules insert themselves between the polymer chains, reducing the intermolecular forces (such as van der Waals forces) that hold the chains together. This allows the polymer chains to move more freely, making the plastic material softer and more flexible.

Overall, the chemistry behind plasticisers is a complex and diverse field that involves the interactions between various chemical compounds and polymer structures to achieve desired material properties.

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Polymeric

Hexanedioic acid, polymer with 1,3-butanediol and 1,2-propanediol, 2-ethylhexyl ester

CAS: 73018-26-5
Polymeric

Hexanedioic acid, polymer with 1,2-propanediol, dodecanoate

CAS: 66456-53-9
Phosphate ester

Triphenyl phosphate

Acronym: TPP CAS: 115-86-6 EC: 204-112-2 Produced by members
Adipate

Diisobutyl adipate

Acronym: DIBA CAS: 141-04-8 EC: 205-450-3 Produced by members
Adipate

Benzyl 2-ethylhexyl adipate

Acronym: BOA EC: 905-983-8 Produced by members
Adipate

Di-2-ethylhexyl adipate

Acronym: DEHA CAS: 103-23-1 EC: 203-090-1 Produced by members

Over the past 25 years, the plasticiser industry invested over 6 billion EUR in R&D, process technology, production, distribution, applications, product safety, sustainability and value chain support. European plasticisers – Summary to an RPA questionnaire Main figures of Plasticisers industry, March 2023

How are plasticisers made?

The process of producing plasticisers involves multiple steps that vary depending on the type of plasticiser being made. The processes may include:

Raw Material Preparation
Getting started begins with the careful selection of raw materials tailored to specific plasticiser needs. This depends on the type of plasticiser that is being crafted and the exact characteristics of the end product. Plasticisers can be fossil based or based on renewable raw materials (natural or biomass balanced) but may also be produced from chemical recycles.
Esterification

Many plasticisers are esters, these are formed by reacting an acid with alcohol. This reaction is typically carried out in the presence of a catalyst and at higher temperatures.

Purification and Distillation

The reaction mixture is purified to remove impurities, unreacted materials, and catalysts. Distillation is commonly used to separate the desired plasticiser product from other components, resulting in a pure plasticiser with the desired properties.

Neutralization and Washing

In some cases, the product is neutralised to remove any remaining traces of acid catalyst. A base, like sodium hydroxide, is added, followed by washing to remove water-soluble impurities.

Stabilisation and Modification (Optional)
Additional steps may be taken to modify the plasticiser’s characteristics, like adding stabilisers to improve heat and light resistance, depending on the desired properties and the structure of the plasticiser.
Quality Control and Testing

Quality control measures are taken throughout the production process to ensure the plasticiser meets desired specifications and regulatory standards. Testing is carried out to check for properties like molecular weight, viscosity, volatility, and compatibility with polymers.

Packaging and Distribution

The plasticiser is packaged and prepared for distribution to manufacturers of plastic products.