This article will examine the different restrictions and indicators currently used to classify coatings as “green.” It will also take a brief look at the organizations and governmental agencies involved in the classification of these coatings and discuss the processes involved. Finally, the author will propose guidelines for development of a universal standard based on existing commonality that would then have to be accepted by the global sanctioning bodies and users, while overcoming the bureaucratic hurdles and other obstacles and challenges in the way.

WHAT IS A GREEN COATING?

The world consensus on green coatings is that there is not a consensus, and this is what causes confusion when projects cross borders or are global in nature. Currently, more and more projects and specifications are international, with specifications being generated globally and materials and labor being sourced worldwide. Standards in China differ greatly from those used in the United States or in the EU. Some countries have no standards at all, some borrow legislation from existing standards and modify pieces, and some districts within these countries restrict many coatings from use.

The most common method of restricting coating use is regulating volatile organic compounds (VOCs) which are emitted from the coating during the application process. However, the method of calculating this value for each coating varies dramatically between countries and can also be theoretical or actual values, both of which usually vary greatly as well.

Coatings, for the purpose of this article, are defined as non-decorative and whose primary use is for asset and corrosion protection. Linings are also discussed and are defined as protecting a substrate, typically metal or concrete, while in an immersed environment. Architectural coatings are often regulated as well, but are also subject to even more restrictions, governmental oversight and regulations.

CAN LOWER VOC CONTENT MAKE A COATING GREEN?

The most common indicator to determine if a coating is green is VOC content, which is measured in grams per liter. And how is this value calculated? Each batch of the same coating will have a different VOC level. Each color of the same product will have a different VOC level. When a color is tinted using pigments, the liquid dispersed colorants typically add VOCs to the coating as well, sometimes as much as 15 percent. To complicate matters further, VOCs can be measured in a laboratory, but can also be theoretically calculated, which typically produces a lower VOC value.

Another challenge is created because chemists measure or calculate VOCs by different standards. Most global coating manufacturers will publish VOC values on their data sheets for the home country or the local standard for those specific regions. The most common standards that are often used include the following.

European Union SED (Solvent Emissions Directive) 1999/13/EC — Common in maritime coatings and OEM-type projects. Applicator may be subject to annual VOC generation limits as well.

European Union PPD (Paint Products Directive) 2004/42/EC (and including various updates) — Used for smaller-scale projects such as refinishing, as well as architectural coatings, but countries and authorities can choose to implement this directive to SED-type projects if they wish. This method considers a VOC as an organic compound having a boiling point greater than 250 C (482 F).

Hong Kong has adopted regulations similar to the South Coast Air Quality Management District (SCAQMD) and is cooperating jointly with Guangdong in mainland China to reduce VOC emissions.1 However, Hong Kong is now using EPA Method 24 to calculate VOCs.2

China followed, but did not rigorously enforce, EU guidelines until 2015, at which time the country passed a VOC Consumption Tax by the Chinese Ministry of Finance. This tax is based on the VOC content of the coating as measured by EPA Method 24, “Determination of Volatile Organic Compound (VOC) content in Paints, Inks, and Related Coating Products.”

South Korea is currently taking steps to improve its relatively high VOC limits as governed by its Air Quality Preservation Law, lowering the allowed limits 10-to-20 percent from their current maximum thresholds. U.S. EPA Method 24 is the primary and most often referred to method for calculating VOC and hazardous air pollutants (HAPs).3

Consistency and homogeneity are not prevalent traits among these standards. Why? They all measure solvent that turns into vapor. However, they are all mathematical formulas that allow for different exemptions, different fluctuations and variances that create different values for the same result. Some of the conflicting calculation methods include: theoretical versus actual VOC content, mathematical versus experimental testing and extrapolations, exclusions and exceptions that compensate for water, specific solvents or container volume. A VOC standard with a global method of calculation would make understanding the greenness of a coating uniform and consistent.

OTHER GREEN INDICATORS

A coating can have a low VOC level, but still be hazardous to the environment or workers. There are several other factors that can taint an otherwise green coating. These include HAPs, ozone-depleting chemicals, banned chemicals, exempt solvents and heavy metals.

HAPs

HAPs are chemicals in VOCs that are particularly harmful to health and/or the environment. HAPs are regulated in many countries, especially in the U.S. Congress amended the Federal Clean Air Act in 1990 and singled out numerous air pollutants that are known to cause, or may reasonably be anticipated to cause, adverse effects to human health or adverse environmental effects. Almost 200 specific pollutants and chemical groups were initially identified as HAPs and the list has been modified over time. Common HAPs include xylene, styrene and toluene. Methyl ethyl ketone (MEK) was on this list until 2005 when the EPA was petitioned by the Ketones Panel of the American Chemistry Council to remove it. A solvent became green overnight. HAPS are often listed separately from VOCs and are considered the second most common indicator of greenness of coatings.

Ozone Depleting Chemicals

Certain hydrocarbons break down when they evaporate from a coating. They are commonly referred to as photochemically reactive solvents or simply reactive solvents. Photochemical reactivity is a measure of to what degree a compound reacts in the atmosphere and contributes to the formation of ozone. The most common photochemically reactive solvents are toluene and xylene. SCAQMD defines photochemically reactive solvents as “any solvent with an aggregate of more than 20 percent of its total volume composed of chemical compounds classified below, or which exceed any of the following individual percentage composition limitations, referred to the total volume of solvent.”

• A combination of hydrocarbons, alcohols, aldehydes, esters, ethers or ketones having an olefinic or cycle-olefinic type of unsaturation: 5 percent.
• A combination of aromatic compounds with eight or more carbon atoms to the molecule except ethyl benzene: 8 percent.
• A combination of ethyl benzene, ketones having branched hydrocarbon structures, trichloroethylene or toluene: 20 percent.

Other solvents are referred to as non-photochemically reactive or nonreactive solvents, as well. Acetone is classified as a solvent with negligible reactivity, meaning that it has no effect on the deterioration of the ozone layer. MEK is classified as a low reactive solvent, which means it has little effect on the depletion of the ozone layer. Coatings containing non-photochemically reactive solvents are typically considered to be greener than those containing photochemically reactive solvents, but can still pose health, safety and environmental (HSE) risks.

Banned Chemicals

Banned chemicals include chemicals banned or prohibited by countries, air regulatory boards and specific facilities. Some chemicals are banned in certain countries, but permitted in others. This can present a problem when a global manufacturer tries to import a coating into a country where some of its raw materials are banned. In 1976, the Toxic Substances Control Act (TSCA) was created and all existing, approved chemicals were assumed safe and were subsequently grandfathered in4. In the coatings industry, raw materials that are used to create global coatings often contain chemicals that do not meet TSCA standards or approvals, causing coating manufacturers to alter their global green coating formulations and create new versions for the U.S. market. Considered by the author to be an outdated regulation, the Act can determine the greenness of a coating.

The EPA’s Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), which regulates pesticides, applies to antifouling coatings in the marine industry and many chemicals in global antifouling paints are banned from application in the U.S.5 However, these coatings can be applied offshore (for instance, in the Bahamas) and then permitted to travel into U.S. waters where the banned substance works as an antifoulant. The greenness of the coating is not altered between country boundaries. So why is a coating green in one country but not in another?

Bisphenol A (BPA) is a component of epoxy resin and a recipient of bad publicity due to health concerns. BPA chemically mimics estrogen in the body and can reportedly affect human development. Ironically, it has been found in the potable water and food-grade linings of major coating companies that are certified as healthy and safe by organizations such as the National Sanitation Foundation (NSF) and the Food and Drug Administration (FDA). Public outcry has effectively killed this chemical as an option for a drinking water or a food-contact lining.

Isocyanates are found in all 100-percent-solids polyurethane coatings, some colorant formulations, and polyurea and polyurethane linings. These linings are considered very green due to their zero-solvent and VOC levels, but their HSE affects can be devastating. Isocyanates are now classified as a carcinogen in animals and potentially in humans, and health concerns from exposure to isocyanates include difficulty breathing, chronic asthma, sickness and reoccurring dermatitis. In fact, phosgene, a chemical warfare agent, is used in the production of isocyanates. Many people have developed isocyanate sensitivity and are dealing with the health consequences and yet, in most countries these coatings are considered to be green. However, many facilities are starting to ban isocyanates from being used in their plants or operations, illustrating that HSE standards and regulations can come from the private sector as well as from governmental regulations.

When public perception can determine whether or not a coating or a component of a coating is green or no longer green, the boundaries will remain vague.

Exempt Solvents

When it was determined that certain chemicals were so prevalent in the coatings industry, and to assure that performance goals could be met in spite of lowering industry VOC levels, the regulatory agencies decided that exceptions to the rules had to be made. In order to allow coatings to perform somewhat effectively while having a minimum impact on the environment, concessions were made to allow certain chemicals to be used, blended, thinned and formulated, and their VOC content would not be considered. Some of the more common chemicals on this list include acetone, parachlorobenzotrifluoride (PCBTF), tert-Butyl acetate (TBAc) and n-Butyl acetate. The irony here is that the VOC levels in these chemicals are quite high, some in excess of 700 g/l. However, they were chosen because of their other environmentally friendly traits, such as non-photochemical reactivity, or for their accessibility, such as acetone. Since they were not necessarily chosen because of their performance levels as a coatings component, manufacturers have had to try to force these randomly selected solvents to integrate with their existing coatings or to formulate completely new coatings in order to achieve the required performance levels and application properties. This has led to compromises in coating performance and has forced the industry to move toward higher-solids products which typically require less solvent or solvents that are exempt or above the boiling point of most VOC-calculated methods, such as benzyl alcohol.

In 2016, SCAQMD decided to review the decision they made almost two decades ago to allow TBAc to remain on its exempt solvent list for VOCs in paint and coatings. When TBAc was initially proposed for exempt status by a chemical manufacturing company in 1997, it was granted an allowance for exemption with the caveat that its long-term health effects would be studied and reviewed over time. Studies in the early 2000s found that there was potential for TBAc to be a carcinogen, and further studies have raised concerns about its toxicity and potential risks to human health. The EPA, however, recently allowed TBAc to be exempt from reporting the VOCs it generates, which reverses a 20-year-old policy. While it appears that TBAc doesn’t have a significant negative impact on air quality, it could pose a serious health risk to workers and users of coatings containing it. Should TBAc lose its exempt status, alternative solvents will have to be utilized, which will have a negative financial impact on the coatings industry. It appears that TBAc, once considered the “perfect green solvent,” is now under scrutiny to determine if it’s really as green as was once promoted.

Heavy Metals

Lead is a heavy metal that was used for decades as an anti-corrosive pigment in many paints, coatings and linings and its negative health effects are well documented. Lead was paired with another heavy metal, chromium (as lead chromate), and used as a pigment in paints to create bright, rich colors. While phased out of consumer paints in the U.S. in the late 1970s, lead was used in many industrial coatings, primers, military formulations and even in traffic paint up until the early 2000s. In fact, lead and chromates are still used today in several coating types. A few years ago, lead chromate was detected in Chinese imported goods from baby toys to steel trusses. Global public outcry caused China to reconsider the greenness of lead and it regulated the export of lead-based paints and the products coated with them. However, the country has only recently decided to restrict the use of lead-based paints within its own borders, finally catching up with the rest of the world’s perception of lead and its ill effects.

CREATING A GLOBAL STANDARD

In order to create one universal standard, the following steps would have to occur.

Common Ground

The major players involved — industry suppliers, regulatory agencies and HSE experts — would have to find a common ground as a starting point. By agreeing on similarities and standardized methods, the goal of a simplified rule package to calculate, regulate and abide by could be achieved.

Minimize Exceptions

There must always be exceptions, but if they could be standardized and minimized to a handful instead of a plethora, they would be easier to understand and comply with. Again, input from the industries’ major players is critical to developing a plan that is both practical and implementable.

Eliminate Inconsistencies

A single method of VOC calculation and benchmark levels that are factually generated instead of arbitrarily created will give a reason and purpose to a VOC value and to subsequent green certification. Currently, we say 100 g/L or 250 g/L is a level of green coating certification, but there is no scientific basis for these lines drawn in the sand. Is a coating that is 107 g/L really significantly less green than a 99 g/L coating, especially if the calculation method is different?

Create One Global Standard for Greenness

Once uniform methods are developed to calculate VOC content, to identify HAPS, and agreements are reached concerning exemptions and banned chemicals — only then can coatings be compared equally.

Conclusion Several acceptable standards and methods for determining the green level of a particular coating or lining do exist. While VOC content has been the benchmark for many years, other chemical traits have been used to improve or diminish greenness levels of a coating. Although several organizations have declared themselves “certifiers of greenness,” in actuality these titles are usually self-proclaimed and financially motivated.

Using existing legislation, regulations and methods as a starting point, standardized and uniform test methods could be implemented, and exemptions and bans universally agreed upon and put into place to create a globally accepted method for determining the green level of a coating. Whether a point system or chromatic color scale is utilized, a simplified, easy-to-understand rating system would provide much clarity to this complex classification.

Reference: Paint Square, Green Coatings from a Global Perspective, date of access: 19 January 2017, http://www.paintsquare.com/archive/?fuseaction=view&articleid=5973