Reactive diluent

Last updated July 30, 2022

Reactive diluents are substances which reduce the viscosity of a lacquer or resin for processing and become part of the lacquer or coating during its subsequent curing via copolymerization. A non-reactive diluent would be a solvent or plasticizer.

Diluents (or thinners) are usually added to lacquers or other resins, to reduce their viscosity and rheology). In thermal cured lacquers, such diluents added are volatile substances which evaporate from the lacquer during drying. In the case of radiation-curing lacquers (for example UV lacquers), those diluents should be avoided. The addition of reactive diluents facilitates the processing of the lacquers, allows the addition of more fillers and improves the wetting behavior on the substrate.^[1] If volatile diluents are replaced by reactive diluents, flammability, smell, skin irritation and environmental compatibility (by lower or no VOC emissions) can be improved.^[2]

Choice of reactive diluent

Since reactive diluents are incorporated into a lacquer or resin and remain in it, they influence not only the viscosity of the uncured lacquer but also its physical properties after curing.^[3] Therefore, the choice of the reactive diluent has an influence on:

The adhesion of the lacquer to the substrate
The compatibility with the binder
The chemistry of the resin (for example an epoxy resin would use an epoxy reactive diluent)^[4]
The flexibility of the cured layer
The volatility
The environmental compatibility.^[5]

Reactive diluents used are low-viscosity, mono-, bi- or polyfunctional monomers or oligomers. In general, several different monomers are combined so that one monomer can compensate for the undesired properties of another monomer. Monofunctional monomers offer a low viscosity, but are quite volatile and tend to smell. With an increasing number of functional groups of a monomer, its volatility decreases while viscosity and crosslinking of the final varnish increase.^[5]

Styrene and acrylates are frequently used as reactive diluents. Epoxides make use of reactive diluents with oxirane functionality.

Related Research Articles

Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also collectively called epoxy. The IUPAC name for an epoxide group is an oxirane.

In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure, or mixing with a catalyst. Heat is not necessarily applied externally, but is often generated by the reaction of the resin with a curing agent. Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.

A photopolymer or light-activated resin is a polymer that changes its properties when exposed to light, often in the ultraviolet or visible region of the electromagnetic spectrum. These changes are often manifested structurally, for example hardening of the material occurs as a result of cross-linking when exposed to light. An example is shown below depicting a mixture of monomers, oligomers, and photoinitiators that conform into a hardened polymeric material through a process called curing.

Polyester resins are synthetic resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Maleic anhydride is a commonly used raw material with diacid functionality in unsaturated polyester resins. Unsaturated polyester resins are used in sheet moulding compound, bulk moulding compound and the toner of laser printers. Wall panels fabricated from polyester resins reinforced with fiberglass—so-called fiberglass reinforced plastic (FRP)—are typically used in restaurants, kitchens, restrooms and other areas that require washable low-maintenance walls. They are also used extensively in cured-in-place pipe applications. Departments of Transportation in the USA also specify them for use as overlays on roads and bridges. In this application they are known as PCO Polyester Concrete Overlays. These are usually based on isophthalic acid and cut with styrene at high levels—usually up to 50%. Polyesters are also used in anchor bolt adhesives though epoxy based materials are also used. Many companies have and continue to introduce styrene free systems mainly due to odor issues, but also over concerns that styrene is a potential carcinogen. Potable water applications also prefer styrene free. Most polyester resins are viscous, pale coloured liquids consisting of a solution of a polyester in a reactive diluent which is usually styrene, but can also include vinyl toluene and various acrylates.

n-Butyl glycidyl ether is an industrial chemical used in adhesives, sealants, and as a paint or coating additive. It is principally used to reduce the viscosity of epoxy resin systems.

Waterborne resins are sometimes called water-based resins. They are resins or polymeric resins that use water as the carrying medium as opposed to solvent or solvent-less. Resins are used in the production of coatings, adhesives, sealants, elastomers and composite materials. When the phrase waterborne resin is used it usually describes all resins which have water as the main carrying solvent. The resin could be water soluble, water reducible or water dispersed.

2-Ethylhexyl glycidyl ether is a liquid organic molecule with formula C₁₁H₂₂O₂ an industrial chemical used to reduce the viscosity of epoxy resins. These are then used in adhesives, sealants, and paints or coatings. It has the CAS Registry Number of 2461-15-6. It has the IUPAC name of 2-(2-ethylhexoxymethyl)oxirane. It also finds use in other polymer based applications.

o-Cresyl glycidyl ether (ortho-cresyl glycidyl ether, o-CGE) is a liquid aromatic organic chemical compound and chemically a glycidyl ether. It has the formula C₁₀H₁₂O₂ and the CAS Registry Number 2210-79-9. It is one of a number of glycidyl ethers available commercially that are used to reduce the viscosity of epoxy resins. These are then further used in coatings, sealants, adhesives and elastomers.

Neopentyl glycol diglycidyl ether (NPGDGE) is an organic chemical in the glycidyl ether family. It is aliphatic and a colorless liquid. It has the formula C₁₁H₂₀O₄ and the CAS registry number of 17557-23-2. It has two oxirane groups per molecule. Its principle use is in modifying epoxy resins.

1,4-Butanediol diglycidyl ether (B14DODGE) is an organic chemical in the glycidyl ether family. It is aliphatic and a colorless liquid. It has two epoxide (oxirane) groups per molecule. Its main use is in modifying epoxy resins especially viscosity reduction.

1,6-Hexanediol diglycidyl ether is an organic chemical in the glycidyl ether family. It is aliphatic compound that is a colorless liquid. It has two epoxide (oxirane) groups per molecule. Its main use is in modifying epoxy resins especially viscosity reduction whilst flexibilizing. It is REACH registered.

1,4-Cyclohexanedimethanol diglycidyl ether is an organic chemical in the glycidyl ether family. It has the formula C₁₄H₂₄O₄ and the IUPAC name is 2-[[4-(oxiran-2-ylmethoxymethyl)cyclohexyl]methoxymethyl]oxirane, and the CAS number 14228-73-0. It is It is REACH registered in Europe. It is an industrial chemical and a key use is in the reduction of viscosity of epoxy resin systems functioning as a reactive diluent.

C12-C14 alcohol glycidyl ether (AGE) is an organic chemical in the glycidyl ether family. It is a mixture of mainly 12 and 14 carbon chain alcohols, also called fatty alcohols that have been glycidated. It is an industrial chemical used as a surfactant but primarily for epoxy resin viscosity reduction. It has the CAS number 68609-97-2 but the IUPAC name is more complex as it is a mixture and is 2-(dodecoxymethyl)oxirane;2-(tetradecoxymethyl)oxirane;2-(tridecoxymethyl)oxirane. Other names include dodecyl and tetradecyl glycidyl ethers and alkyl (C12-C14) glycidyl ether.

Trimethylolpropane triglycidyl ether (TMPTGE) is an organic chemical in the glycidyl ether family. It has the formula C₁₅H₂₆O₆ and the IUPAC name is 2-[2,2-bis(oxiran-2-ylmethoxymethyl)butoxymethyl]oxirane, and the CAS number 3454-29-3. It also has another CAS number of 30499-70-8 A key use is as a modifier for epoxy resins as a reactive diluent.

Castor oil glycidyl ether is a liquid organic chemical in the glycidyl ether family. It is sometimes called castor oil triglycidyl ether. It has the theoretical formula C₆₆H₁₁₆O₁₂ and the CAS number 14228-73-0. The IUPAC name is 2,3-bis[[(E)-12-(oxiran-2-ylmethoxy)octadec-9-enoyl]oxy]propyl (E)-12-(oxiran-2-ylmethoxy)octadec-9-enoate. A key use is acting as a modifier for epoxy resins as a reactive diluent that adds flexibility and improved mechanical properties.

C12-C13 alcohol glycidyl ether is a mixture of organic chemicals in the glycidyl ether family. It is a mixture of mainly 12 and 13 carbon chain alcohols, also called fatty alcohols that have been glycidated. It is an industrial chemical used as a surfactant but primarily for epoxy resin viscosity reduction. It has the CAS number 120547-52-6.

Trimethylolethane triglycidyl ether (TMETGE) is an organic chemical in the glycidyl ether family. It has the formula C₁₄H₂₄O₆ and the IUPAC name is 2-({2-methyl-3-[(oxiran-2-yl)methoxy]-2-{[(oxiran-2-yl)methoxy]methyl}propoxy}methyl)oxirane. The CAS number is 68460-21-9. A key use is as a modifier for epoxy resins as a reactive diluent.

Poly(propylene glycol) diglycidyl ether (PPGDGE) is an organic chemical in the glycidyl ether family. There are a number of variations depending on the starting molecular weight of the polypropylene glycol. They have the formula (C₃H₆O)_n.C₆H₁₀O₃ and the IUPAC name is Poly[oxy(methyl-1,2-ethanediyl)],a-(2-oxiranylmethyl)-w-(2-oxiranylmethoxy)- A key use is as a modifier for epoxy resins as a reactive diluent and flexibilizer. It is REACH registered.

Diethylene glycol diglycidyl ether (DEGDGE) is an organic chemical in the glycidyl ether family with the formula C₁₀H₁₈O_5.. The oxirane functionality makes it useful as a reactive diluent for epoxy resin viscosity reduction.

Phenyl glycidyl ether, is a liquid aromatic organic chemical in the glycidyl ether class of compounds. It has the formula C₉H₁₀O₂. It has the CAS Registry Number 122-60-1 and the IUPAC name of 2-(phenoxymethyl)oxirane. A key use is in the viscosity reduction of epoxy resin systems. It is REACH registered and on EINECS under the name 2,3-epoxypropyl phenyl ether.

References

↑ Bodo Müller, Walter Rath: Formulierung von Kleb- und Dichtstoffen – das kompetente Lehrbuch für Studium und Praxis. 2. Auflage. Vincentz Network, Hannover 2009, ISBN 978-3-86630-862-6, S. 149–150
↑ Reinhold Schwalm (2007), UV Coatings (in German), Amsterdam: Elsevier, pp. 112–114, ISBN 978-0-444-52979-4
↑ Jagtap, Ameya Rajendra; More, Aarti (2022-08-01). "Developments in reactive diluents: a review". Polymer Bulletin. 79 (8): 5667–5708. doi:10.1007/s00289-021-03808-5. ISSN 1436-2449.
↑ Monte, Salvatore J. (1998), Pritchard, Geoffrey (ed.), "Diluents and viscosity modifiers for epoxy resins", Plastics Additives: An A-Z reference, Polymer Science and Technology Series, Dordrecht: Springer Netherlands, vol. 1, pp. 211–216, doi:10.1007/978-94-011-5862-6_24, ISBN 978-94-011-5862-6 , retrieved 2022-03-29
1 2 Stefan Pieke (2010), Experimentelle Untersuchungen zur effizienten Vernetzung von Oberflächenbeschichtungen mit UV-Strahlung, Karlsruhe: KIT Scientific Publishing 2010, p. 12, ISBN 978-3-86644-452-2

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[Müller-1] Bodo Müller, Walter Rath: Formulierung von Kleb- und Dichtstoffen – das kompetente Lehrbuch für Studium und Praxis. 2. Auflage. Vincentz Network, Hannover 2009, ISBN 978-3-86630-862-6, S. 149–150

[Schwalm-2] Reinhold Schwalm (2007), UV Coatings (in German), Amsterdam: Elsevier, pp. 112–114, ISBN 978-0-444-52979-4

[3] Jagtap, Ameya Rajendra; More, Aarti (2022-08-01). "Developments in reactive diluents: a review". Polymer Bulletin. 79 (8): 5667–5708. doi:10.1007/s00289-021-03808-5. ISSN 1436-2449.

[4] Monte, Salvatore J. (1998), Pritchard, Geoffrey (ed.), "Diluents and viscosity modifiers for epoxy resins", Plastics Additives: An A-Z reference, Polymer Science and Technology Series, Dordrecht: Springer Netherlands, vol. 1, pp. 211–216, doi:10.1007/978-94-011-5862-6_24, ISBN 978-94-011-5862-6 , retrieved 2022-03-29

[Pieke-5] 1 2 Stefan Pieke (2010), Experimentelle Untersuchungen zur effizienten Vernetzung von Oberflächenbeschichtungen mit UV-Strahlung, Karlsruhe: KIT Scientific Publishing 2010, p. 12, ISBN 978-3-86644-452-2

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