The phrase “Reducing VOCs” is easily interpreted differently, depending on an individual’s function and interest. One may interpret it as existing and evolving technologies and techniques to achieve any reductions in Volatile Organic Compounds. Any discussion should include approaches that are a bit unheralded or relatively unknown as well.
Another elucidation would be to review the latest changes in regulations regarding VOC reductions and current levels. Even that is complex, with differing regulations in various US geographies as well as large global variances.
And yet another would be to discuss the differences between VOCs, HAPs (Hazardous Air Pollutants) and Exempt Solvents. This article will address all to some degree. And although VOCs are usually viewed as man-made, there are many examples of naturally-occurring VOCs.
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Defining and measuring VOCs
In any of the cases, there has to be a reliable and reproducible method to measure baseline VOCs, and any variance after any changes are made in a system. Even in that regard, the methods differ and the definition of VOCs vary by country/region:
Country/region | VOC definition | Regulatory Body |
Canada | organic compounds that have boiling points roughly in the range of 50 to 250 °C (122 to 482 °F) that would effect air quality | Health Canada |
EU | Any organic compound having an initial boiling point less than or equal to 250 °C (482 °F) measured at a standard atmospheric pressure of 101.3 kPa. | VOC Solvents Emissions Directive REACH |
China | Compounds that have originated from automobiles, industrial production and civilian use, burning of all types of fuels, storage and transportation of oils, fitment finish, coating for furniture and machines, cooking oil fume and fine particles | Chinese EEP |
India | monitors oxides of nitrogen (NOx), sulphur dioxide (SO2), fine particulate matter (PM10) and suspended particulate matter (SPM) (does not differentiate VOCs) | Central Pollution Control Board |
United States | 40 CFR 51.1000, volatile organic compounds refer to any compound of carbon which participates in atmospheric photochemical reactions; excludes carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates and ammonium carbonate. | EPA, OSHA, CARB Test methods: EPA 24, ASTM D6886 and SCAQMD method 313 |
Exempt solvents
The list of exempt solvents – those that are not considered to be photochemically reactive and therefore do not contribute to SMOG or air pollution – has been vacillating globally to include/exclude one or two materials. In the US, the current exempt list consists of:
- Acetone
- t-butyl acetate
- dimethyl carbonate
- propylene carbonate
- parachlorobenzotrifluoride (Oxol 100)
- methyl acetate
- methylene chloride
- 2-amino-2-methyl-1-propanol (AMP-95)
The South Coast Air Quality Management District (SCAQMD) in California is considering the elimination of the exempt status of t-butyl acetate and parachlorobenzotrifluoride (PCBTF) and the latter is expected to be restricted in China in May 2019.
Reducing VOCs
The initial intent of VOC reduction – to decrease air pollution – was a good idea, but the technologies that were immediately used did not result in the same quality of paints as of their predecessors. In some cases, the net effect was probably worse with the increased frequency of painting. In the last 15-20 years, there have been innovations in many areas which have allowed for the development of paints that are equivalent to and in most cases outperform their predecessors.
Latex technologies have allowed for reduced VOCs. Examples include structured latexes and the emergence of core-shell technology to manufacture lower minimum film formation temperature (MFFT) polymers.
The resins can coalesce at very low levels of solvents while performing at levels only seen with very high glass transition temperature (Tg) polymers in the past. Particularly with high gloss paints, properties such as hot block resistance, open time and flow-levelling are achieved within the current VOC regulations. Chiefly with exterior coatings, a large challenge is the development of early properties so that unexpected precipitation or temperature drop don’t affect long-term performance.
Some commercial paints still rely on a combination of hydrophobic coalescents that can contribute early- and longer-term property development. Dowanol™ PM and TPnB are an example of one such combination. The first provides early property development and is fairly volatile, while the second is not nearly as fugitive, and remains in the film quite a while. One of the more useful tools I have used over the years is the Eastman Solvent Selector Chart [PDF], which lists a variety of solvents and hard-to-find information such as Hansen Solubility Parameters.
Other emergent coalescing technologies to reduce VOCs include Eastman OptiFilm™ Enhancer, Oxsol 100 and EPS® 9147. In addition, companies such as Vertec Biosolvents have developed soy-based solvents. VertecBio Gold® is partially composed of soy methyl esters, with offsets to several petroleum-based VOC-contributors. Cargill produces Methyl Soyate which is soy-derived and also has many applications to replace petroleum-based products and reduce VOCs.
In solvent based paints and their polymers, different approaches have been taken. Most alkyds were at a relatively high solids level, but required somewhat strong solvents to provide manageable viscosity. There have been breakthroughs in molecular weight, branched structures and co-polymerization to produce novel technologies to reduce VOCs.
In waterborne polyurethanes, acetone and other materials have replaced N-Methyl-2-Pyrrolidone (NMP) as a process aid and plasticizer to help reduce the VOC of the resins. In addition, 100% solids epoxies and urethanes exist that provide the equivalent wet applied and dry film thicknesses and emit zero VOCs.
Another approach that will not be addressed here in depth, is the use of reactive coalescents, which become a part of the coating and are minimally or not volatile.
Additional information on regulatory information can be found through Prospector, as well as technical data sheets and starting point formulations using technologies that aid in VOC reduction.
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Thanks Marc! Good information.
Hi Mark,
Nice concise article! Very informative.
Ron Lewarchik
Thanks Mr. Hirsch. This is a nice concise article. However, what about using reactive coalescing agents or diluents?
Sure. That is an excellent suggestion.
I think reactive coalescents and diluents are exempt in the EU (such as styrene in body fillers) as they are transformed into non VOC’s as part of the curing process.