In order to understand the role of VOCs (Volatile Organic Compounds) and solvents in the coatings industry, it is important to first look at the timeline of US legislation on air quality and understand how we got to where we are now concerning solvent environmental regulations.
- The first US federal legislation related to controlling air pollution was the Air Pollution Control Act of 1955. It provided funding for federal research into air pollution but didn’t have the mandate to act – more research than anything else.
- In 1963 The Clean Air Act became the first US federal legislation addressing air pollution control itself.
- In 1967 the Air Quality Act expanded the federal government’s role by, for the first time, performing comprehensive air monitoring studies and stationary source assessments.
- The Clean Air Act of 1970 established the Environmental Protection Agency (EPA) with the role of policing industry to reduce or eliminate air pollution. This legislation applied restrictions on the level of VOCs that were allowed in coatings.
The EPA defines a VOC as “organic compounds that have a high vapor pressure and low water solubility.” On hot summer days, VOCs react with nitrogen oxides and form ozone – an air pollutant.
A vast majority of the industrial solvents used in coatings are considered VOCs and are regulated by the EPA. The primary use of a solvent in a coating (both VOC and non-VOC) is to lower viscosity to achieve proper application and flow. If you were to take away the solvents from most coatings, they would be way too thick to apply or use in most industrial applications.
Popular VOC Solvent Types Used in Paint
Aliphatic solvents are mixtures of long straight-chain, branched-chain, or cyclic paraffins. VM&P Naphtha and Mineral Spirits are common aliphatic solvents.
Aromatic solvents have a benzene ring structure. Toluene, Xylene, and Aromatic 100 are common aromatic solvents used in the coatings industry. They can range from “slow” to “fast” evaporation.
Alcohols such as Methanol, Ethanol, and Isopropanol are some of the types of alcohol used in coatings. They are generally good solvents for polar resins. “Small” alcohols are soluble in water and as the chain gets longer (i.e., 2-ethyl hexanol for example) the water miscibility lessens.
Esters include solvents like Butyl Acetate and Ethyl Acetate. They generally have a smell that isn’t too harsh and have good solvency in most coatings.
Ketones include solvents like Methyl Ethyl Ketone (MEK) and Di Isobutyl Ketone. They range from very fast to slow in evaporation rate. Overall, they have very good solvency due to their double bond between carbon and oxygen atoms. Their odor in many cases can be very strong.
Glycol Ethers include solvents like Ethylene Glycol Mono Butyl Ether (Butyl Cellosolve) and Propylene Glycol Normal Butyl Ether (PNB). They generally have slow evaporation rates and are a staple for water reducible coatings.
Some VOCs react slower than others and do not contribute to air pollution as much as others. This type of VOC is considered exempt under EPA rules and regulations. Some of the most recognized VOC exempt solvents are;
- t-Butyl Acetate (TBAC)
- Parachlorobenzotrifluoride (PCPTF)
- Acetone
- Methyl Acetate
- Propylene Carbonate
- Dimethyl Carbonate
In the United States, the VOC of a coating is reported as the weight of the VOC released from one gallon of coating less water or other exempt solvents. Below are a couple of examples using theoretical calculations:
Coating Without Exempt Solvents
Pounds of VOC – 100
Gallons of Paint – 100
VOC = 100 # of VOC / 100 Gallons of Paint = 1# VOC per gallon.
Coating With Exempt Solvents
Pounds of VOC – 100
Pounds of Exempt – 100 (with a weight per gallon of 10#/gallon)
Gallons of Paint – 100
VOC = 100# / (100 gallons of paint – 10 gallons of exempt) = 100#/90 Gallons = 1.11# VOC per gallon (excluding exempt).
Some Basic Characteristics of VOC Exempt Solvents
- t-Butyl Acetate (TBAC) has good solvency and compatibility with many industrial resins. It has a manageable flashpoint (72-88F) and evaporates around three times faster than butyl acetate.
- Parachlorobenzotrifluoride (PCBTF) is considered a “slower” evaporating solvent – like Aromatic 100. It is an extremely popular solvent in the coatings and adhesive industries. It is currently under scrutiny regarding its cancer potency as reported by the NTP (National Toxicology Program).
- Acetone is a ketone with very good solvency and evaporates quickly – sometimes too quickly to use as a flow and leveling solvent. It is highly volatile and flammable with a flashpoint near zero Fahrenheit.
- Dimethyl Carbonate is considered a fast-evaporating solvent – somewhat faster than TBAC. It is polar – and oddly enough – has a freezing point around 40°F which makes it hard to use if you store solvent drums outside in the winter.
Note that water is the most common solvent used in water reducible coatings but isn’t organic, therefore not a VOC.
A conventional “low VOC” coating may contain both typical VOCs and exempt VOCs to balance the formulation for application and performance. The goal is to provide the customer with the coating they need but be conscientious of government regulations and the environment.
Changing regulations will ultimately mean developing new compliant formulations.
Finding VOC-exempt solvents that match the solvency, cost, odor, evaporation rate, flash point, compatibility, and surface tension can be a significant undertaking. Many hours of testing and re-formulating occurs in low VOC coatings to match higher VOC counterparts and these changes typically mean higher costs for manufactures and end-users.
Formulators are constantly looking for and evaluating formulation strategies that will keep costs to a minimum and develop coatings that meet the performance needs of their customers. Marcus Paint has made great progress in supplying compliant coatings to our customers. We are committed to providing products that contribute to a clean and safe environment and truly making a difference for future generations.
Contact Us today if you have questions about VOCs and solvents, or their role in coatings