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VOCs: Bumpy ride came before smoother finishes

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For the last half-century or so in the United States, we have devoted a lot of attention and resources to cleaning up the environment. As applied to coatings, the primary emphasis has been on reducing the amount of smog-causing solvents used in our paints and finishes. These solvents are called VOCs (volatile organic compounds).

As I wrote in the September 2011 issue of Woodshop News, VOC regulations as applied to coatings formulators and finishing shops are extremely confusing because they differ so much from one place to another.

But one thing is clearly evident when you look at the changes in these regulations since the mid-1960s. Our understanding of the relationship between solvents and smog, which is more technically referred to as ground-level ozone, has become increasingly sophisticated.

Early history

Los Angeles has suffered the most from smog of any American city and it launched an attempt to reduce the problem in 1966 with “Rule 66.” This rule was quite minimal and crude compared to current VOC regulations in that it exempted whole classes of solvents thought to be less a problem than others. So it wasn’t very difficult for formulators to design around the rules.

During the 1970s many states enacted regulations similar to Rule 66.

But by then Congress had entered the picture by passing the Clean Air Act of 1970. This act established the Environmental Protection Agency, which was tasked with setting national standards for air quality. In addition, the law directed states to develop plans to meet those standards.

Major revisions to the Clean Air Act were made in 1977. These defined a VOC as any organic compound that reacts photochemically in sunlight with nitrogen oxides (produced primarily by automobile engines) to generate ground-level ozone. To reduce this ozone-creating smog, states were directed to come up with plans to limit the pounds of solvents per gallon in paints and finishes.

Though coatings contribute a very small amount to smog (compared, for example, to industrial pollution and automobiles), these directives led to two changes in solvent-based formulating: a greater emphasis on high-solids coatings and a greater use of lower-density solvents.

Higher-solids finishes such as conversion varnish, polyester and, eventually, UV-cured-finishes release less solvent per square foot covered because more of the liquid in the can is a solid.

Because VOCs were measured as pounds-per-gallon (or grams-per-liter), using solvents with lower densities reduced the weight of solvent in the can, thus reducing the VOC content by definition.

To illustrate the complexity of choosing non-problematic solvents, consider that in the 1980s some coatings manufacturers began using 1,1,1-trichloroethane, also known as methyl chloroform, because it was classified as a VOC-exempt solvent. Until, that is, it was discovered that this solvent participated in depleting the upper-level ozone because of its long atmospheric lifetime.

Industry fights back

Congress got back in the act in 1990 with more amendments to the Clean Air Act. These amendments, which were largely directed at reducing acid rain in the Midwest and Northeast, also tightened restrictions on paints and finishes.

States were given a deadline to adopt regulations that would clean up the air in “non-attainment” areas — those areas that didn’t meet the standards. Also, areas that did meet the standards were instructed to establish regulations that would maintain the clean air.

The tightened regulations were enough to get the coatings industry to fight back.

The trajectory of the fight was similar to that in other industries, including the automobile industry, which fought the requirements to install seatbelts and raise gas mileage. First there is resistance, usually through lawsuits against the government, then reluctant acceptance and finally commitment to developing the technology to make compliance possible.

The resistance within the coatings industry used the argument that coatings contributed so little to ground-level ozone that the price paid in loss of performance would far outweigh any gains in reduced pollution.

A typical example, especially in Southern California, which was outlawing oil-based paints, was that the latex substitutes required more frequent repainting because they didn’t wear as well. Thus, it was questionable whether there was any reduction in ozone creation at all.

New methods of measuring

Just as happened in other industries, within a few years the coatings industry turned its attention to solving the problems of maintaining or improving performance while reducing ground-level ozone.

To do this, the emphasis changed. With the cooperation of the EPA, regulations changed from emphasizing “low-VOC coatings” to designing for “low-ozone coatings.” It was the ground-level ozone, after all, that was the problem — not VOCs alone. Rural areas didn’t have an ozone problem, no matter how high the VOC levels from coatings, animal manure, etc. So research into how each solvent participates in causing ground-level ozone was intensified.

Traditionally, VOCs had been regulated using what was called a “mass-based” approach. A solvent was either photochemically reactive with nitrogen oxides or it wasn’t. But little or no distinction was made among the individual solvents. Now a distinction was made.

So, for example, if a formulator were to substitute one or more negligibly- or medium-reactive solvents for a highly reactive solvent, the polluting effect could be reduced significantly without losing any of the performance characteristics. This is what is now being done and it’s the reason lacquers won’t soon disappear no matter what the rumors.

The degree of reactivity of various solvents was established and published so formulators could substitute one or more of the less reactive solvents for a bad one and still maintain solvency (dissolving the resin), viscosity (so the coating could be sprayed) and drying rate.

Computer programs that used Hansen/Hildebrand solubility parameters to identify the candidate solvents for substitution helped immensely in redesigning the formulations. These solvents would then be tried and the resulting coating tested to see if it performed close enough to the more polluting coating to be acceptable.

Along the way, some solvents have been “delisted,” meaning that they have been classified as negligibly reactive. These include, acetone, methyl acetate and parachlorobenzotrifluoride (PCBTF). Most important for the finishes we use is acetone.

If you look at a MSDS of a compliant lacquer, you’ll more than likely see that it contains a lot of acetone. This solvent has been critical to the continued availability of lacquers, even in Los Angeles.

Acetone evaporates very rapidly, however, so a slow evaporating “tail” solvent has to be included to give the finish time to flow out and eliminate orange peel. You’ll see this solvent (or solvents) listed also.


After initial industry resistance and a continuing claim by some observers that all finishes will soon be water-based, the coatings industry pulled itself together and figured out how to continue making the solvent-based finishes most of us like to use and effectively reduce pollution at the same time. We are all better off for what has been accomplished. 

Bob Flexner is author of “Understanding Wood Finishing” and “Flexner on Finishing.”

This article originally appeared in the January 2014 issue.

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