Volatile organic compounds

By: Julián A.  Restrepo

RestrepoCurrently, the situation in the Latin American paint market is characterized by a preponderance of solvent-based products, while at a global level, the current orientation of paint production is aimed at the development of coatings with low solvent content, both for economic and ecological reasons. Research, design and development for the formulation of coatings in recent years, as well as future studies, take into account above all the requirement to respect the conservation of the environment as much as possible, this mainly means reduction, elimination or partial or complete replacement of organic solvents.

Obviously, the most important factor by which conventional paints contribute to environmental pollution is the emission of solvents. This is how the most technologically advantaged countries have enacted legislation aimed at reducing emissions of this type of compound [1].

In addition to the environmental problem they cause, solvents are flammable substances, so they have a fire risk both in their manufacture and use. So every time, there is a stronger pressure to reduce the use of these.

To define the content of solvent and volatile material associated with paints, the term Volatile Organic Compounds or VOCs is used. We must mention that in English, depending on the source consulted, in many cases VOCs are spoken of indifferently referring to Volatil Organic Compound, content or component.
Undoubtedly, the acronym VOC refers to solvents and hydrocarbon compounds... but really, what does VOC mean?

Different definitions
In reality, the number of definitions you have is very broad and almost as large as the number of existing regulations. This is where you have a problem in the formulation of solvent-based systems that present a global utility, since the definitions of VOCs are different in each part of the world, which makes a painting can meet the limits of VOCs in some countries, but in others not, which would constitute a trade barrier that is difficult to overcome.

Thus, the fact that there are such a large number of definitions of VOCs indicates that the confusion around VOCs begins in their definition. Therefore, several of the most representative definitions of VOCs in different parts of the world will be presented, aiming to give a global look at their definition.

The European Union (EU), under the scheme of "eco-denomination", defines VOCs as: "Any organic component that under normal pressure conditions, has an initial boiling point less than or equal to 250 ºC".

But taking into account the version of the EU solvent directive, we have: "Any organic component that at 20 ºC has a vapor pressure greater than 0.01 kPa, or that has the corresponding volatility under the particular conditions of use" [2].  In this sense, some authors claim that the EU has the simplest definition of VOCs.

So, one definition taking into account the previous two is: "Any organic compound with a boiling point less than 250 ºC and vapor pressure greater than 0.01 kPa at 20 ºC, is considered a VOC" [3].  This definition only considers the volatility of the solvent in the classification. Also, the EU requires a compound to be on the EINECS (European Inventory of Existing Commercial Substances) list which includes compounds registered as industrial materials of hazardous composition and known harmful effects on health.

Like the EU, the US has a definition of non-volatility, but in the latter it is more restrictive. The rule that determines the classification of a VOC in the U.S. is RULE 24 of the EPA (Environmental Protection Agency): "The percentage of material that does not evaporate after one hour at a temperature of 110 ° C is not volatile."

In addition to the volatility of a compound, U.S. laws allow consideration of a material's contribution to air pollution.  As is known, the generation of tropospheric ozone requires the presence of VOCs and nitrogen oxides (NOx) in the air. This is how the  U.S. has a second definition of VOC: "Any organic component involved in atmospheric photochemical reactions, except those designated by the EPA that possess negligible photochemical reactivity."

In addition, there are other considerations in the use of chemicals in the U.S. In a part of the clean air decree of 1977 the U.S.  government issued a list of HAPs (Hazardous Air Pollutans). The list of 313 compounds includes aromatic solvents, aliphatics, ketones, esters, among others.  In certain regions of the U.S. it is prohibited to use these solvents, and it is always advisable to formulate products without PAH solvents to avoid conflicts with environmental standards.

In Australia, the paint approval scheme defines VOCs as: "Organic compound with a vapour pressure greater than 0.01 mmHg at 21 °C, and with a boiling point of less than 250 °C." [2].
In Mexico, the government definition of VOC is: "Any material that evaporates at a temperature of 155ºC in an hour." Thus, liquids normally considered as plasticizers such as PDO (dioctyl-phthalate), are considered as VOCs by Mexican legislation.

The states of the Geneva Protocol define: "Unless specified, VOCs are all organic compounds of an anthropogenic nature, other than methane, that are capable of producing photochemical oxidants by their reaction with nitrogen oxides, in the presence of sunlight." The observation of organic compounds other than methane reflects the fact that methane is much less reactive in the atmosphere than are hydrocarbons of higher molecular weight [4].

Finally, in mathematical terms, the definition of voC content in a painting is made based on [5]:

a)If all the solvent in the formulation is considered as VOC for regulatory purposes, then:

(b)If water is present in the formulation, it should be subtracted from the solvent content, then:

Conclusions
The fact that a varied number of definitions of VOCs are presented in different parts of the world, indicates that there is no clear and congruent environmental legislation of global utility (in times of commercial expansion), which can generate conflicts between international markets.

Although it is clear that in the definition of VOC it is only possible to exclude water and non-volatile compounds.

The usefulness of developing products with low levels of VOCs translates into: Greater safety in production and application, lower emissions, lower levels of air pollutants and ultimately, more environmentally friendly coatings.

In reality it can be said that the global trend is directed towards the reduction of the solvent content in paints, but not its elimination completely, since otherwise the legislation would require a content of zero VOCs, which does not happen in reality, and instead, many of these countries are known to  have a maximum permissible VOC value for certain paints and sectors.

In order to reduce the levels of VOCs in paints, manufacturers have begun to develop a number of technologies, such as: Coatings with high solids content, water-based coatings, coatings by high energy curing (or ultraviolet-UV curing), solid coatings (powder), and the use of solvents less harmful to the environment. There are even products for the formulation of solvent-based paints with reactive diluents and in water-based paints with reactive coalescing.

*I.Q. Research, Design and Development
 SAPOLIN PAINTS
[email protected]

References

[1] Pulgarín, D. F. and Restrepo, J. A. "Reduction of Volatile Organic Compounds (VOCs) through water-based technology in wood coatings". Thesis National University, Headquarters Medellín, 2002.

[2] Robe, G. and Stout, R. "Solvents to reduce VOC levels". Inpralatine. Ed. 29. Vol. 45, #6, 2000.

[3] Kershaw, Y. "VOC legislation on the threshold of change", European Coat. Journal, 4. 1998.

[4] DeNevers, N. Air Pollution Engineering. Ed. Mc GrawHill. Mexico, 1997.

[5] ASTM D 5201-91. "Calculating formulation physical constants of paints and coatings", 1994.