Driven by consumer demand and regulatory pressure, paint and coating formulators, along with makers of chemical additives for those markets, have brought to the forefront products with improved environmental and health performance
Modern paints and coatings are complex mixtures of film-forming substances, fillers, pigments and a host of additives (see “Paint Components,” below). Many of the compounds traditionally used in paint and coating formulations present significant environmental and human health risks. Spurred by tightening regulations and growing demand for healthy and sustainable products on the part of end-users, the paints and coatings industry has delivered a wide range of materials with significantly improved environmental and health properties. And thanks to a continued focus on innovation, many of the newer environmentally friendly paints and coatings have begun to achieve parity with conventional products in performance.
“The drivers behind the development of sustainable paints are really a combination of both regulatory pressure and consumer demand,” says Chris Connelly, director of brand management at Benjamin Moore (Montvale, N.J.; www.benjaminmoore.com). “The development started as a way to comply with environmental regulations, but now, consumers, contractors, and facility managers are more aware of the social and environmental impacts of products, and are demanding paints with lower environmental and health impact.”
In general, the advancements in paint and coating technology related to environmental impact have come as a result of several factors, including the development of better formulation technology and the availability of new additive options. “The current state of the art is a result of an accumulation of many small innovations that have added up to large advancements in the environmental performance of paints,” says Chris Cook, director of the Planet Possible program at AkzoNobel (Amsterdam, the Netherlands; www.akzonobel.com).
“The technology of environmentally friendly paints has expanded significantly over the last 10 years and this technology expansion was enabled by innovation,” says Murray Hemsley, global market leader for Architectural & Protective Coatings at Eastman Chemical Co. (Kingsport, Tenn.; www.eastmanchemical.com). “The primary focus across both architectural and industrial coating applications has been on technology that enables maximum performance while still meeting stringent volatile organic compound (VOC) and emission requirements,” he remarks.
In addition to paint formulators developing better methods for combining paint components, the companies supplying them are also now looking for ways to deliver more environmentally sustainable chemicals to use in their formulations. AkzoNobel’s Cook says his company, along with others, are now pushing harder on suppliers to engage in more sustainable practices.
Paint can be considered a liquid mixture that, when applied to a substrate, converts to a solid film. Paints are varied and can be very complex. Most paints are composed of the following four major categories for paint ingredients: binders (the film-forming component); the solvent (to allow the application of the liquid to a surface); pigments (to impart opacity and color); and additives (to modify application and finish properties).
Binders. Paint binders bind the pigment molecules to form a film and bind the film to the substrate. Binders are usually synthetic or natural resins, such as alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene, polyurethanes, polyesters epoxies and others. Binders are sometimes categorized by the mechanisms for drying or curing. The binder material often surrounds particles of pigment materials. The drying process involves the evaporation of the solvent, as well as typically an oxidative cross-linking process for the polymers in the binder.
Solvents. The solvents carry the nonvolatile parts of the paint and control the viscosity of the paint during the application process. For waterborne paints, water is the solvent, while solvent-borne paints can have a variety of organic compounds, including aliphatic hydrocarbons, aromatic compounds, ketones, alcohols, esters, ethers and others.
Pigments. Pigments are generally granular solids that are incorporated to give the paint color. Titanium dioxide, pthalo blue and red iron oxide are often used to give paint opacity and color. Engineered molecules and dyes are often used in paints as well.
Additives. Usually added in small amounts, paint additives can have a significant impact on paint properties. Common categories for additives include rheology modifiers, surfactants, driers, foam-control agents, anti-settling agents, wetting agents, biocides and others.
Low-VOC paint performance
Historically, one of the major environmental challenges associated with paints and coatings has been due to high levels of VOCs and other species that can have negative effects on indoor air quality, contribute to smog formation and adversely affect long-term human health (see “VOC Health Effects, Limits and Measurement,” below).
“Modern paint makers have moved away from the old model of making paints with solvents like ketones, toluene and other organic solvents,” explains William Golton, a former industry consultant and former analytical chemist at DuPont. “Now, all the VOCs in most paints come from the additives, and in many cases, the high-VOC additives are now being substituted by higher-boiling compounds that have the same effect on the paint properties,” he says.
AkzoNobel’s Chris Cook continues, “The development of more sustainable paints is an extension of the long-running trend to ‘greener’ products, and the movement away from solvent-based products is expanding from wall paints to the trim and wood-care products market, including stains, varnishes, lacquers and polyurethanes. Paints have largely made that switch, already, but other product sectors are doing the same.”
Lowering VOC levels in paints has been a central area of innovation for the paint industry, says Golton. “For low-VOC automotive finishes, it remains more difficult to achieve comparable performance to solvent-based products at the same cost than it is for paint at this point,” he says. “The challenge there is that it is a bigger technological leap to go from a solvent-borne product to a waterborne product than it is to substitute additives in a product that is already waterborne.”
“In the architectural-coatings industry, low-VOC is no longer a specialty product offering; it is a must-have option for all brands in the space,” says Mary Ellen Shivetts, senior product stewardship manager for PPG Architectural Coatings (Pittsburgh, Pa.; www.ppgac.com) in the U.S. and Canada.
The shift to new materials has required much effort to negotiate the tradeoffs that arise among the various attributes of paints and coatings. “In the past, the perception was that a better environmental profile necessarily meant a sacrifice of performance, but the industry has improved significantly in both environmental and paint performance, a tradeoff between the two may not be necessary,” says AkzoNobel’s Cook.
Eastman’s Murray Hemsley agrees: “Companies understand that consumers are not usually willing to trade off quality for sustainability, and through hard work and formulation expertise, paint formulators are very close to matching the performance of conventional paints [with their low-VOC products].”
AkzoNobel’s Cook says performance improvements for low-VOC paints have been made “across the board, but especially at the higher price points.” One issue that remains for low-VOC is glossiness — a high-gloss finish with no brush marks is still hard to achieve with water-based products, Cook notes.
VOC Health Effects, Limits and Measurement
Although definitions for volatile organic compounds (VOCs) can vary depending on the context, the key aspects for paints and coatings involve organic compounds with low boiling points that can undergo chemical reactions in the atmosphere as a result of interaction with ultraviolet radiation. Aliphatic hydrocarbons, acetone, ethyl acetate, glycol ethers and others are VOCs that have been used as ingredients in paint and coating formulations. Health effects of VOCs generally depend on the concentration in the air, and on how long and how often a person breathes the air. Acute effects can be eye, nose and throat irritation, nausea, headaches and exacerbation of asthma symptoms. Chronic exposure to high levels of VOCs can increase the risk of certain types of cancer, liver and kidney damage and the risk of damage to the central nervous system. For more information on health and VOCs, visit the Indoor Air Quality Scientific Findings Resource Bank (iaqscience.lbl.gov).
In the U.S., VOCs in paints are regulated by the Environmental Protection Agency (EPA; Washington, D.C.; www.epa.gov). Federal VOC limits are now set at 250 grams per liter (g/L) for flat paints and 380 g/L for others. The establishment and evolution of VOC limits for paint has seen a large degree of input from industry. “The whole history of VOCs in paint is a good example of how industry can work with government to produce win-win situations,” Golton says. There are now much better-performing paints with much lower VOC content. So the public got less pollution and the paint manufacturers got better paint.
Some states and regions have lowered the VOC levels for paints that can be legally sold in their areas beyond those required by U.S. federal regulations. For example, California’s standards are more stringent: 150 g/L for nonflat finishes and 100 g/L for flat. In areas where smog can be a public health problem, the limits go further. The South Coast Air Quality Management District (SCAQMD; Diamond Bar, Calif.; www.aqmd.gov), the air-pollution control agency for the areas surrounding Los Angeles, has set an even more ambitious limit — 50 g/L of VOC for all finishes. So-called “super-compliant” products meet a standard of less than 10 g/L, explains Sam Atwood of the SCAQMD. He says that over the past 20 years, more than 50 ton/d of VOC emissions have been reduced from architectural coatings through four major rule amendments and a fee/reporting rule adopted in 2008, which has provided incentive to manufacturers to further lower VOC emissions.
Legislation to limit and lower VOC emissions are becoming more common elsewhere also. The European Union has reduced VOC limits in regulations put forth in 2007 and again in 2010. Also, its REACH legislation on chemical toxicity affects VOC use. China is moving to limit VOCs because of air-quality issues resulting in part from rapid development.
Measurement. Measurement of VOCs has historically been an imprecise process. EPA’s Method 24 is said to be unreliable for paints with very low levels of VOCs. At lower VOC levels, the test has had a difficult time achieving accurate measurements. In its new GS-11 standard (see “Third-Party Certification,” below), GreenSeal says it has incorporated a more direct method into the standard that produces a more accurate reading as the amount gets smaller. The test is estimated to be 10 times more effective and improves further as the VOC gets closer to zero
“The old Test Method 24 was set up a long time ago, when a lot of the companies didn’t have big laboratories,” says former consultant Golton. “That meant it had to be easy to do, but the rudimentary test was never intended to measure VOC levels below 100 g/L.” A newer test method, ASTM D 6886 is based on gas chromatography, and has gained wide acceptance in the U.S. A similar method is the standard in Europe.
The SCAQMD is aware of those drawbacks and uses Method 313-91, which is supposed to be more accurate for no- and low-VOC paints. Although companies acknowledge the unreliability of Method 24, it remains the only method that can be used for certification. The EPA has not yet revised Method 24 to give manufacturers another option.
While the proliferation of low-VOC (designated by VOC levels lower than 250 g/L) coatings products continues, there is a considerable push to achieve much lower levels than that in many market segments. Paint sellers such as Benjamin Moore, Sherwin-Williams and several others have pushed the VOC levels lower, to a point where they can be marketed as “zero-VOC” paints. Truly zero-VOC paints do not exist, says former industry consultant Golton, but the levels in these paints are less than 5 g/L of VOCs in order to be classified as “zero-VOC.”
Benjamin Moore’s zero-VOC product lines Natura and Ultra Spec are among the growing offerings. “In the past you could expect lower levels of durability, or perhaps different application characteristics [for zero-VOC],” says Glenn Cooper, vice president of product development for Benjamin Moore, “but we have really conquered those issues now.”
Health risks also have decreased. The zero-VOC Natura brand, for example, has been certified asthma- and allergy-friendly by the Asthma and Allergy Foundation of America, Cooper notes.
PPG offers the PPG Pittsburgh Paints Wonder-Pure brand, a zero-VOC interior latex paint and related primer with low odor, which allows painters and maintenance professionals to paint in occupied spaces with little disruption, PPG says.
Although typically accounting for only 0.5–5.0 wt.% of a paint, additives play a critical role in the paint’s properties, including those having to do with environmental and health impact. Research and development investment over the past several years on new additives for paints and coatings is now bearing fruit. Chemical companies are offering new options for paint formulators to reduce environmental impact.
For example, Eastman’s MAK (methyl n-amyl ketone) and MIAK (methyl isoamyl ketone) solvents help offer routes to reduce VOC emissions in coatings applications. MAK and MIAK are high-boiling specialty ketones with good solvent activity and slow evaporation rates. They allow paints to achieve higher solids and lower emissions while maintaining excellent flow and leveling properties and optimal spray viscosities, Eastman says.
Eastman’s Hemsley says there have been innovations in ultra-low VOC and zero-emission coalescents, molecules that help emulsion-based paints form a film as the water evaporates. Also, specialty cross-linking monomers have been introduced to polymer manufacturers, which enable the polymers contained in paint to perform at a higher level while delivering low-VOC-emission formulations.
Eastman’s Texanol and Optifilm products allow water-borne polymers to be used in architectural paints rather than requiring an organic solvent-based system. “Optifilm enhancer 400 allows the film-forming mechanism to take place without emissions,” Hemsley says. Texanol ester alcohol helps the discrete water-borne polymer particles to coalesce and form a strong durable film, he adds.
For industrial coating applications, Eastman cellulose-ester products, such as the family of Eastman Solus performance additives, allow for rheology control and metallic flake orientation within higher-solids, lower-emission coatings.
Dow Coating Materials (Philadelphia, Pa.; www.dowcoatingmaterials.com) has also introduced several paint-additive products that can help reduce environmental impact and lower VOC content. For the industrial coatings market, Dow has developed technology for improving the performance of waterborne alkyd coatings. Alkyds are polyesters modified by adding fatty acid molecules, and they have been used for industrial coatings because of their excellent finish properties. But low-VOC regulations have reduced their use in many regions, Dow says, and waterborne alkyd emulsions haven’t matched the performance of solvent-borne alkyd systems. Dow has developed technology to disperse traditional high-viscosity, short-oil alkyds with minimal surfactant and no polymer modification. These attributes allow for the formulation of pigmented waterborne alkyd coatings with comparable dry times, adhesion and hardness to those of conventional solvent-borne alkyd coatings.
In the architectural coatings market, Dow has also developed binder materials that can be formulated at lower VOC levels, but that maintain the hardness properties of a higher-VOC paint. Typical approaches to develop lower-VOC paint formulations can result in films with a tacky feel. Dow investigated post-film-formation polymer crosslinking chemistries and worked on optimizing particle morphology for latex particles. The company’s optimized binders, including its RHOPLEX 800h Binder, showed a significant improvement in hardness profile.
In October 2015, Dow introduced ROVACE 10 Emulsion, a low-VOC emulsion with high (55%) solids content. The product was designed for easy processability and requires little or no coalescing solvents, allowing lower VOC content, the company says.
In Europe, Perstorp AB (Stockholm, Sweden; www.perstorp.com) has expanded production of its polycaprolactone polyols products, which can be used as a building block to make waterborne polyurethanes with low VOC profile, David James, VP of innovation surface technology, Perstorp, explains. Polycaprolactone polyols are a type of polyester made with a ring-opening polymerization process, rather than a condensation polymerization reaction. Perstorp’s polycaprolactone products, known as Capa, have low viscosity, so they can act as solvents in paint, lowering the need for VOC-containing components, James says.
Lanxess AG (Cologne, Germany; www.lanxess.com) has taken aim at improving the environmental impact of processes to make inorganic paint pigments. Specifically, the company will start production of red pigments using a new, more sustainable process. For more, see February Chementator section.
Reflecting the growing consumer demand for products with positive sustainability characteristics, third-party certification organizations focused on sustainability have become a major factor driving the development and use of low-VOC paints and coatings. An example is the not-for-profit organization GreenSeal (Washington, D.C.; www.greenseal.org), which released in December 2015 an updated and expanded standard for architectural coatings. Knowns as GS-11, the revised standard is designed to encourage paint formulators to use chemicals with less risk to human health and the environment. In order to meet the standard, and thus be able to earn GreenSeal’s emblem on product labels, the “products must restrict carcinogens, toxins affecting reproduction, hazardous air pollutants, heavy metals, formaldehyde, certain phthalates and other chemicals,” GreenSeal says. “The standard also ensures that certified paints, coatings, stains and finishes still deliver the same functional performance that consumers expect from conventional architectural coatings,” GreenSeal adds. Green Seal’s certification process involves criteria based on scientific research, an in-depth review of product data, manufacturing procedures and claims on product labels, and an on-site audit of facilities. Periodic monitoring is required to maintain certification.
Another example of third-party certification comes from the U.S. Green Building Council (USGBC; Washington, D.C.; www.usgbc.org), the organization responsible for LEED (Leadership in Energy and Environmental Design) certification in new buildings. The LEED rating system offers a credit toward LEED certification for buildings that use low- or zero-VOC paints in construction or renovation projects. The credit covers VOC emissions into indoor air and the VOC content of materials, as well as the testing methods by which indoor VOC emissions are determined.
The USGBC’s Brendan Owens says the organization is trying to guide project teams to make better decisions related to sustainability. “In terms of paints, we are looking at primarily two areas: the environmental impact of the manufacturing process, and the environmental and human health impact of the paint when applied.” The main criteria for paint are emissions, material sourcing, sourcing disclosures, disclosure of chemicals and optimization of material ingredients to minimize the use of environmentally problematic chemistries where possible, Owens explains.
He notes that 80% of the over 70,000 projects that have applied for LEED certification earn the paint credit. “LEED is a huge driver for the ‘built environment’ now, and the offerings for low-VOC and environmentally friendly paint products are better than ever before.
Dimensions of sustainability
Although a key issue, VOC content in paint is not the only concern for environmental impact. In addition to VOC levels, durability, recyclability, functionality and other factors can have an impact on paint “green-ness” and sustainability profile. AkzoNobel’s Cook remarks that making paints more environmentally friendly can involve lowering paint’s carbon footprint by using lower-carbon formulations and improving the logistics for upstream raw materials.
In addition, advances in durability can make a difference — longer lifetimes for paint mean that even a product with a higher environmental impact initially could be better overall if the paint lasts longer than the other products and does not have to be applied as often.
“As the low- and zero-VOC paint space progresses, we find that consumers will be looking at additional ways to be environmentally friendly, such as using recycled paints or paints made from bio-renewable resources, or participating in post-consumer paint recycling programs,” says PPG’s Shivetts
Another focus for developing better environmental performance in paints and coatings is part of a wider trend to add specific functionality to paints and coatings.
For example, AkzoNobel has developed exterior paint technology that helps buildings stay cooler in warm weather, and thus lower the energy costs associated with cooling them. AkzoNobel’s KeepCool and SunReflect brands are designed for use in tropical climates, and have been used in Asia since 2014. By carefully selecting pigment molecules that do not absorb infrared (IR) radiation, the exterior paint can reflect more IR and prevent it from heating up the building walls. External testing has shown that the new AkzoNobel paints can reflect up to 90% more IR radiation than comparable exterior paints. This could translate into energy savings of 10% on a 15-story building, or higher in a small bungalow, AkzoNobel says. Another example of an environmentally relevant additive is the company’s Dulux Guardian coating products, which can absorb air pollutant species by incorporating charcoal additives into the paint.
Many of PPG’s zero-VOC products, including its PPG Paint Pure Performance brand, incorporate a mold- and mildew-resistant compound that makes the dry paint film resistant to a range of mold species.