Until recently, solvents have been used rather unhesitatingly. The priority has always been to find an efficient and cheap product for the respective application. However, the use of “classical” solvents is being regarded increasingly critically in relation to environmental protection and occupational health & safety. Another major issue is their sustainability. Over time, it has become apparent that many chemicals, and especially solvents, not only have properties that make them attractive for different technical applications, but are also potentially harmful to human beings and the environment.
For a long time, the comparatively high prices of “green chemistry” substitutes largely prohibited their use. Hence, formulations would only be switched over when regulations no longer allowed the use of classical solvents.
The increasingly strict conditions in more recent years have led to greater environmental awareness, leading more and more to the reduction and substitution of poisonous or hazardous substances for more environmentally sound alternatives, and to keeping a closer eye on sustainability. Today, appropriate and affordable solutions based on renewable resources exist for the vast majority of applications.
Dibasic Esters: Alternative Solvents
Dibasic esters (DBE) are mixtures of methyl esters of adipic, succinic and glutaric acid, and are available in all kinds of mixture ratios (and some even as “uncut” pure product). Also available is a blend of isobutyl esters of these acids.
Like other solvents already presented, the DBEs are among the modern environmentally friendly alternatives to conventional solvents. DBEs are essentially VOC-free, have a very high flashpoint and are biodegradable, noncorrosive and nontoxic. DBEs are clear, colourless liquids and have a mild, fruity, very acceptable odour. That means DBEs can be used in most applications without hesitation.
DBEs can be used as substitutes for just about every conventional solvent, but especially highly volatile, aromatic solvents and even the highly controversial products methylene chloride and n-methyl pyrrolidone. DBEs are readily soluble in alcohols, ketones, ethers and most hydrocarbons, but only slightly soluble in water and higher paraffinic hydrocarbons.
Despite the entirely positive ecological and health-related properties of the product, DBEs stand out for excellent dissolving power that can even dissolve hardened surfaces.
The main applications are
- Lacquers and paints (versatile use; most noteworthy are coil and can coatings, textile printing inks, wood lacquers for children’s toys, inks for food packaging etc.)
- Paint strippers
- Binders (in particular foundry resins)
- Solvent mixtures for cleaning purposes (e.g. cleaning electronic components, injection moulds, PU equipment etc.)
- And much more
SOLKETAL: EHS-friendly and sustainable
One out of those solvents is Isopropylidene glycerin also known as SOLKETAL (4-hydrox-ymethyl-2,2-dimethyl-1,3-dioxolane / CAS 100-79-8). The homology of this solvent is based on the underlying ring system of the 1,3-dioxolane and the hydroxymethyl group in the fourth position. As a result of this, it is first and foremost a primary alcohol, while it is also a cyclical ether at the same time. Solketal is a cyclical ketal and has two methyl groups.
The raw material for Solketal is substandard glycerine (SSG) as used in biodiesel production. It is of utmost importance that this SSG is produced on a purely plant basis. This way, Solketal can be truly called a sustainable solvent.
Solketal is a low-viscosity liquid (~11cP (@25° C) at room temperature and its freezing point is far below zero (approx. -26,5° C). Even though the vapour pressure levels of Solketal at 20° C may be 0.1 mbar, the substance can be included in the group of high boilers showing a boiling point of about 190° C.
Solketal is a practically universal and very compatible substance. It is completely miscible with cycloaliphatics and aromatics as well as dissolves to a large extent in vegetable oils. There is miscibility to a sufficient extent even with nonpolar substances like aliphatics. Also ethers and hydrocarbons
go well with Solketal. But probably the most important and outstanding characteristic is the complete miscibility with water.
To make clear statements about the solubility of certain polymersystems in Solketal, it will definitively require Tests for the specific application. However the excellent solvent capacity for resins like polyesters, polyacetates, polyacrylates, epoxides, polyurethanes, urea-formal-dehyde- and melamine resins, has been known and well documented in the literature for many years. Even more complex macromolecules
such as polyesterimides can be dissolved by Solketal, too. As a matter of fact this would allow to Substitute “classical” solvents to a large extent.
Solketal is harmless, non-toxic, non-irritant and has – if any – only a slight but pleasant odour, hence is highly compatible in contact with human beings. It is neither dangerous nor required to be identified. It is also environmental friendly. Aside from its excellent properties as a solvent, Solketal is also suitable for adjusting rheological properties and can be used as a dispersion aid, emulsifier and wetting agent. Solketal can furthermore develop lacquer-forming properties and thus influence film formation and drying.
The diversity described allows a wide range of applications:
- Adhesives Resins
- Cleaning agents
- Paints and coatings
- Paint strippers
- Pharmaceutical, veterinary and cosmetic products
- Printing inks
- Surface active substances
|Acid Number||max.||0.2 mgKOH/g|