Reactive diluents are substances which reduce the

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

of a lacquer or resin for processing and become part of the lacquer or

coating A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. Pow ...

during its subsequent curing via

copolymerization In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...

. A non-reactive diluent would be a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticiz ...

. Diluents (or thinners) are usually added to lacquers or other resins, to reduce their viscosity and

rheology Rheology (; ) is the study of the flow of matter, primarily in a fluid (liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with Plasticity (physics), plastic flow rather than deforming Elasticity (phy ...

). 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 In processed animal foods, a filler is an ingredient added to provide dietary fiber, bulk or some other non-nutritive purpose. Products like corncobs, feathers, soy, cottonseed hulls, peanut hulls, citrus pulp, screening, weeds, straw, and cere ...

and improves the wetting behavior on the substrate.Bodo Müller, Walter Rath: Formulierung von Kleb- und Dichtstoffen – das kompetente Lehrbuch für Studium und Praxis. 2. Auflage. Vincentz Network, Hannover 2009, , S. 149–150 If volatile diluents are replaced by reactive diluents, flammability, smell, skin irritation and environmental compatibility (by lower or no VOC emissions) can be improved.

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. 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) *The flexibility of the cured layer *The volatility *The environmental compatibility. Reactive diluents used are low-viscosity, mono-, bi- or polyfunctional

monomers In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification Mo ...

oligomers In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

. 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 In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...

of a monomer, its volatility decreases while viscosity and crosslinking of the final varnish increase.

Styrene Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...

and acrylates are frequently used as reactive diluents.

Epoxide In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale ...

s make use of reactive diluents with oxirane functionality.

References

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