The growing problem of invasive mussel species in the Great Lakes has prompted researchers to create innovative solutions aimed at preventing their spread to inland lakes and reservoirs. These mussels attach to various surfaces, both in the upper (epilimnion) and deeper (hypolimnion) layers of lakes. During the winter months, mussels will die off, leaving the large structures constructed of their shells on the lakebed. Their colonies recede into the deeper waters where water temperature is warmer than the icy conditions on the surface. In the spring and summer, the mussels return shoreward, recoating the left-behind shell structures and adding layers of shell material to the submerged landscape. Juvenile mussels are released from fish hosts and can migrate or float to nearly any structure or vehicle, with bilge water from ships often transporting them to new locations. Once attached, mussels begin their reproductive cycle, and this adherence is key to their spread. If prevented from attaching, they are forced to relocate, increasing competition for space and resources.

To combat fouling, researchers have developed a clear, tri-cure hybrid silsesquioxane coating that is inexpensive, easy to apply, and safe for aquatic environments. When applied to glass or fiberglass, materials they readily attach to, this coating prevents the bonding of mussel proteins to surfaces, making them resistant to fouling. By coating boat hulls, boat owners can reduce mussel attachment, slowing the spread of invasives, saving on costly maintenance, reducing drag, and contributing to the protection of other aquatic ecosystems.

Introduction

Marine biofouling, which is the undesirable accumulation of microorganisms, plants, and animals on submerged surfaces, poses significant operational and environmental challenges to maritime industries and aquatic infrastructure.^1-3ÌýThe consequences of biofouling are far-reaching. It causes increased hydrodynamic drag on vessel hulls which reduces fuel efficiency and speed, while simultaneously contributing to higher greenhouse gas emissions.^4-7ÌýIn addition, biofouling accelerates the corrosion of submerged metal and concrete surfaces, clogs pipelines in coastal and nuclear facilities, and disrupts water flow and nutrient exchange in aquaculture systems.^8,9

One of the most practical and effective strategies for mitigating biofouling is the use of protective surface coatings or coating additives. These are broadly classified into biocidal and nonbiocidal types. Biocidal coatings rely on the controlled release of toxic agents from a polymer matrix to prevent organism settlement and are considered antifouling coatings.¹⁰ÌýThe efficacy of such coatings is governed by the biocide’s release rate and its environmental compatibility that should ideally combine strong antifouling activity with low toxicity and moderate fresh and sea water solubility. Unfortunately, only a limited number of biocides meet these stringent requirements for safe and sustained marine use.¹¹

Nonbiocidal coatings primarily include fouling-resistant and fouling-release coatings (FRCs). Fouling-resistant coatings are typically based on hydrophilic polymers such as poly(ethylene glycol) (PEG) and zwitterionic materials, which prevent initial organism adhesion.¹²ÌýHowever, their tendency to swell in saline environments leads to poor mechanical performance. In contrast, FRCs utilize hydrophobic, low-surface-energy materials that allow weakly adhered organisms to be easily removed under mild shear forces. Polysiloxanes are commonly used as FRCs and offer excellent thermal and photochemical stability, though their long-term performance is limited by hydrolytic degradation. To overcome these limitations, hybrid organo-silicon coating systems have been developed. These systems integrate organic and inorganic elements to combine durability, antifouling characteristics, and environmental resilience.^13,14ÌýFor instance, R-alkoxysilanes, particularly methoxy and ethoxy variants, have long been employed to consolidate porous substrates like stone by forming crosslinked siloxane networks with the ratio [RSiO_3/2], or silsesquioxanes that also contain organic bridges. When incorporated into coatings, these networks offer benefits such as low thermal conductivity, oxidative resistance, and mechanical integrity.

Among silicon-oxygen-based coating systems derived from alkoxysilanes, tetraethoxysilane (TEOS) is a widely used precursor.^15,16ÌýHowever, its slow curing rate often necessitates acidic or basic catalysts and long reaction times. As an alternative, photocuring methods that utilize photoinitiators to trigger rapid organic polymerization under light have gained popularity for enabling fast curing without complex handling or component separation. Moreover, using R-functional trialkoxysilanes with epoxy, amine, thiol, or fluorocarbon side groups allows tailoring of surface adhesion, hydrophobicity, and internal stress relief within the final silsesquioxane-based coating.¹⁷

Bioinspired approaches have further guided the design of antifouling surfaces. Many plants and insects feature microstructured, waxy coatings that combine hydrophobicity with self-cleaning properties. Mimicking these strategies, coatings with nanoscale surface roughness and low-surface-energy materials (e.g., fluoropolymers) have been developed to enhance water repellency and reduce biological adhesion.

Introduction

Per- and polyfluoroalkyl substances (PFAS) have been used historically in paint formulations for their hydrophobic and oleophobic properties in addition to their surface properties. In waterborne coating formulations, they are often present as fluorosurfactants (FS). This study explores the development of high-performance waterborne coatings that do not require fluorosurfactants and maintain or exceed the performance of legacy FS-containing systems.

Architectural coatings are expected to deliver a balance of performance properties. Among the most critical performance attributes is block resistance, especially in high-traffic and high-touch environments such as kitchens, bathrooms, cabinetry, and institutional settings. Removing fluorosurfactant from formulations often leads to trade-offs in performance, particularly in block resistance, tack resistance, and durability. Traditional approaches to improve block resistance, such as increasing pigment volume concentration (PVC), raising glass transition temperature (T_g), or adding waxes, can negatively impact gloss, durability, or VOC content. Therefore, another approach is necessary.

By optimizing polymer design, focusing onÌýT_g, particle morphology, crosslinking, and monomer selection, this research demonstrates that coatings can achieve excellent block resistance, tack resistance, washability, and durability without the use of fluorosurfactants. Comparative performance data across gloss levels and environmental conditions validate the efficacy of these optimized systems, offering a resin-based approach to eliminating FS from waterborne acrylic coating formulations.

This article presents a comprehensive study on the development of an optimized all-acrylic polymer system that eliminates fluorinated additives while maintaining or improving key performance metrics.

Materials and Methods

This study focuses on an all-acrylic polymer that does not contain fluorosurfactant while delivering high-performance properties. A high-gloss (HG) polymer was specifically designed to achieve gloss levels above 80 GU at 60°, with a minimum film formation temperature (MFFT) of 21 °C and utilizing self-crosslinking monomer.

Resins with higherÌýT_gÌýor elevated MFFT typically exhibit desirable hardness characteristics, such as reduced surface tack. However, increasing hardness often requires additional coalescent, which can raise VOC levels in the final coating formulation. To balance these factors, the HG polymer was engineered to minimize coalescent demand while maintaining surface performance. The incorporation of a self-crosslinking monomer further enhanced hardness without increasing VOC content, as crosslinking occurred after film formation rather than during application. The resin system was evaluated against an FS-containing control resin.

Four coating base formulations using the optimized polymer are shown inÌýTable 1. The deep base formulas in this study were tinted with 12 oz of colorant per 100 gal.

Experimental

The following tests were conducted.

Hot Block Resistance

Hot block resistance was evaluated with a 3-mil drawdown dried at 70 °F and 50% relative humidity (RH). Small squares were cut at dimensions of 1.5 in. by 1.5 in. and the coated sides were placed together and put in a 120 °F oven with a 1000 g weight on top. Then, samples were kept at room temperature for 30 min before the samples were pulled apart and the block resistance was rated on a scale of 0-10, with a rating of a 0 indicating fully adhered, and a rating of 10 indicating no adhesion and the squares pulled apart from each other with essentially no force needed.

Cotton Ball Tack Resistance

The tack resistance of the HG surface was evaluated by allowing the coated sample to dry for 24 h under controlled conditions of 70 °F and 50% RH. After drying, a cotton ball was placed on the surface, and a 500 g weight was applied directly on top. The setup was then transferred to an oven and exposed to 120 °F for 60 min. Following heat exposure, the sample was allowed to rest at room temperature for 30 min. After this rest period, the cotton ball was removed and evaluated for cotton residue.

High-Traffic Durability

The “light switch test” was conducted to simulate high traffic and high contact conditions. Lotion was applied to half of each test panel and allowed to sit for 2 h. After the exposure period, the lotion was wiped off, and the panels were stained with a combination of mineral oil and a dirt particulate, as well as a rusty water solution. These stains were allowed to dry for 2 h before being wiped with a paper towel. The panels were then subjected to 100 wash cycles using a sponge and a nonabrasive scrub medium. Finally, the color change (ΔE) of the stains was measured to assess the coating’s chemical resistance and ability to resist softening and staining.ÌýFigure 1Ìýshows a panel that was prepared and washed.

The construction industry is experiencing a paradigm shift from focusing solely on sustainability to embracing comprehensive resilient design, driven by increasingly severe weather events and rising financial risk. While sustainable design emphasizes minimizing environmental impact and resource conservation, resilience—the capacity to adapt and maintain functionality after a disturbance—demands a systems-based approach that addresses future-looking hazards like high winds, hail, fire, and flooding. This article argues that true durability requires building materials, including advanced coatings, to work collaboratively as integrated systems to resist extreme loads that exceed minimum building code requirements. It explores current design resources like LEED v5 and FM Global standards, and provides specific examples of how materials are engineered to resist hazards. These examples include multilayer roofing systems designed for very severe hail, and innovative coatings and membranes used in water-retention assemblies to manage urban storm runoff. Ultimately, resiliency is redefining what it means to create durable, lasting buildings, positioning systems-level thinking—rather than isolated product properties—as the foundation for a future-proof built environment.

Introduction

Resilient design has become a catchphrase within the construction and architecture communities. Over the last two decades, forward-thinking designers and building owners have focused not just on the now, but on the future, when determining their designs. This challenge started with a focus on sustainability. The U.S. Green Building Council (USGBC) defines sustainable design as “creating places that are environmentally responsible, healthful, just, equitable, and profitable.”¹ÌýSustainable solutions often refer to minimizing the burden on the natural environment, recycling, and conserving energy and other natural resources. These goals have created a multitude of industry buzzwords, including durability, recycled content, energy efficiency, and carbon neutral. However, sustainability is not the same as resiliency.

Resilience is defined by the Resilient Design Institute as “the capacity to adapt to changing conditions and to maintain or regain functionality in the face of stress or disturbance. Resilient design solutions often consider durability as well as the ability to keep a building functional after a weather event.”²ÌýSolutions such as having a generator to maintain power are very resilient, though not necessarily sustainable (Figure 1). To be truly resilient, designers and building product manufacturers must look at more than product properties such as Volatile Organic Compounds (VOC) and embodied carbon, often the go-to for sustainable design, and more at materials working together as systems. There is no one property that ensures resilience. Designers and manufacturers need to collaborate to create complete systems of materials that work together to achieve a successful outcome. The ultimate goal is for designed solutions to meet both sustainability and resiliency targets, such as slowing the release of storm water to prevent overloaded sewers while also using some of the captured rainwater for irrigation.

One example of resilient design is the Sand Palace, which was one of the only structures left standing in its area after Hurricane Michael in 2018. Built specifically to withstand severe storms, the house utilized advanced materials like insulated concrete forms (ICFs) and was designed to resist winds of up to 250 mph, significantly exceeding state building codes at the time. The homeowner explained that they deliberately went “above and beyond code” when making material and design decisions by consistently asking, “What would survive the big one?” It is estimated that the house cost 15-20% more as a result of these decisions. Although they did have to replace utilities and experienced the loss of the first floor along with one of the air handlers, the overall damage was minimal compared to the surrounding properties.

Resiliency has become an important design strategy for many reasons, but the primary driver is money. It is expensive to rebuild after severe weather events, and insurance companies are noticing. In some parts of the United States, it is becoming more expensive and more difficult to get insurance, particularly in coastal regions and areas prone to wildfire. For example, a 2024 report from the Senate Budget Committee shows that the nonrenewal rate in Florida increased 280% between 2018 and 2023.³ÌýAdditionally, FM Global, one of the largest insurers of commercial properties, continues to expand the areas where their buildings must meet very severe hail requirements.

On the residential side, prospective homebuyers are paying attention to the potential weather impacts on properties. In 2024, Zillow started posting hazard ratings for climate-related impacts such as flood, wildfire, wind, heat, and air quality on property listings.⁴ÌýAs with other trends within the construction industry, significant attention is paid when there are clear drivers to profits and losses. This article introduces published resources and references being used by designers to design for resilience. It then looks closely at specific examples in which coatings and other building materials work together as systems to withstand increased building loads.

Polyurethane (PU) networks exhibit the outstanding mechanical strength, thermal stability, and solvent resistance that is required for use in high-performance coatings, adhesives, and composites. However, the most common way to form these polymer networks is to use hazardous isocyanate-functional molecules. Moisture-cure urethane silane polymers have recently been used to form hybrid PU networks, thereby mitigating end-user exposure to hazardous isocyanate during application. However, while the applicator is not exposed to isocyanates, they are nonetheless used to synthesize these polymers. High-oleic soybean oil (HOSBO) was chosen for use in hybrid binders to explore potential beneficial properties, mainly enhanced hydrophobicity and reduced viscosity, and as a U.S.-produced renewable chemical, the fatty acid groups offer beneficial properties. For this project, isocyanate-free polyurethane-silane binders were formed by first reacting diethanolamine with HOSBO to form fatty acid diols, followed by transcarbamation reactions to form urethane linkages. The polymers were then end-capped with various secondary aminoalkoxysilanes via subsequent transcarbamation reactions. Reaction of these polymers with atmospheric moisture resulted in crosslinked hybrid networks with siloxane linkages. Surface-free energy (SFE) as well as thermal and mechanical energy were explored.

Introduction

Crosslinked polymer networks are in numerous consumer and industrial products, ranging from coatings for medical devices to foams for seat cushions.^1-4ÌýThe chemistry for these networks typically involves urethane, urea, ether, and thioether chemistries.^5-7ÌýAmong these, polyurethane and polyurea networks remain the most widely studied due to their rapid and efficient formation at room temperature, the ability to modify the backbone structure, as well as their excellent thermal and mechanical properties.^8,9ÌýThe most common way to form polyurethane networks requires the use of hazardous isocyanates.⁸ÌýHowever, isocyanate exposure can lead to a myriad of health issues, including skin and eye irritation, symptoms of asthma, and sensitization upon exposure.^10,11

A way to synthesize crosslinked networks while avoiding isocyanates is to make networks with siloxanes where an alkoxysilane is used as a crosslinker. These urethane-siloxane polymers also have the advantage of producing crosslinked networks with enhanced properties from the sol-gel region.^12-16ÌýFor example, silane-terminated polyurethane and poly(urethaneimide) networks demonstrate improved thermal stability, good adhesion to metals, elastomeric properties, and excellent moisture resistance.^17-20

In addition to avoiding isocyanates, there is interest in the polyurethane field to shift from petrochemical to renewable biobased raw materials, particularly soybean oil.^21,22ÌýPolyurethane networks are not necessarily hydrophobic and often rely upon incorporation of other materials and segments to make hydrophobic material.²³ÌýThe addition of the fatty acid chains is predicted to enhance hydrophobicity. Other benefits from the fatty acid chain include reduced viscosity and, by using the high oleic oil, reduced yellowing with a high content of chains with a single unsaturated group. Hybrid urethane-siloxane vegetable oilbased polymers have even been formed through isocyanates^24-27Ìýand cyclic carbonate chemistry.^28-30ÌýThe isocyanate-based networks have the same toxicity issue of the nonhybrid polyurethane while the cyclic carbonate-based networks form pendant hydroxyl groups, which may limit any enhancement to hydrophobicity. Rather than use these methods, the ester linkages of the oil can be utilized to incorporate other organic functionalities, such as alcohols and diols, which can be further reacted.³¹

Herein, a method is provided to form polyurethane-silane networks that circumvents the use of isocyanates and incorporates renewable biobased materials. In this work, a safer acylation reagent, 1,1′-carbonyldiimidazole (CDI), was used to form the urethane functional groups. These acylating groups were used to attach the fatty acid-based diol, which is based on high-oleic soybean oil (HOSBO), to the alkoxysilane crosslinker and to add chain extenders. These compounds were then used as binders to form clear polyurethane-siloxane networks. To our knowledge, there are no reports of polyurethane-siloxane networks based on HOSBO. This method allows for greater control of structure of the binders. Chain extenders have been explored in the binders. Thermal, mechanical, and surface properties of the resulting crosslinked networks were determined using several analytical techniques and compared with those of a control network.

Q: What role will formulation innovation play in advancing sustainability?

The formulation stage is key to achieving our sustainability goals. An old mentor of mine compared formulating to cooking. He would say that it’s not just about using the finest ingredients, but how you blend them together. Understanding how one ingredient influences and brings out the best in the next—and how they combine to define the consistency and taste of the final dish. I absolutely share that view.

Formulators know that if you change one component, it can affect the whole formulation: its stability, possible component aggregation, solids settling rate, pH range, viscosity, shear resistance, and film drying time. Getting the formulation right determines in-can behavior and therefore shelf life, as well as influencing coating application (e.g., spraying). New raw materials (like biomaterials) must be properly integrated to enable efficient manufacturing and effective industrial-scale application.

Significant R&D work is focused precisely on this topic. For example, clients who come to us looking for support with their formulation development are exploring the use of new or alternate raw materials, transitioning to water-based systems or reducing VOC (volatile organic compound) levels, and evaluating new formulations on numerous application processes to become more efficient and less energy intensive.

Q: Historically, sustainability and performance have often been seen as trade-offs. Do you believe that tension is narrowing, and why?

Yes, absolutely. Firstly, we’ve seen a change of mindset within the industry. This is not just a growing awareness but an actual acceptance that change is inevitable, and that thinking and acting sustainably is the only way forward. And secondly, innovation is advancing. Given the right motivation and encouragement, I believe we as an industry are capable of achieving great things.

The introduction of any new material (e.g., from sources independent of fossil fuels) is always accompanied by initial teething problems. It’s the nature of the game. But those problems can be overcome through innovation cycles. We gain a greater understanding of the new raw materials, their properties and behavior, and how best to integrate them into formulations that meet, or even exceed, the performance of current state-of-the-art coatings.

Recent innovations have already demonstrated a closing of the gap. The use of reactive polymer-bound surfactants has led to the development of durable, water-based latex coatings for exterior use. In Europe, Worlée is pioneering the use of sustainably made camelina oil in the manufacture of high-performance binders and additives. And Evonik has recently introduced a range of 100% plant-based biosurfactants (made via the fermentation of sugar) that exhibit enhanced wetting and color retention properties in waterborne coatings.

Q: How important is lifecycle thinking, including durability, maintenance cycles, and end-of-life considerations, when determining whether a coating is truly sustainable?

In the past, there was a tendency within our industry (when supplying to OEMs) to consider the sale of a coated end product as a convenient boundary for where our responsibility ended. Ease of application, appearance, performance, and a certain lifetime would encourage the OEM to buy more coating. But there was little consideration for what came after that.

Now, however, we are entering a period of increased accountability. And if we as chemists create a complex material (and a coating is certainly a multi-component complex system), then we are responsible for its makeup, its behavior, and the environmental impact throughout its lifetime. This begins with the sourcing of raw materials, continues through the energy usage and pollution evaluations of manufacturing and application, and now extends to beyond the lifetime of the coated end product. As more and more end products are evaluated for their potential to be reused, recycled, or even composted, we as an industry need to extend our considerations to that end-of-product-life moment.

This will pose one of our greatest challenges. For example, how do we get a protective coating that has been designed to weather the harshest environmental conditions to stop protecting, on demand, and break down into recyclable or biodegradable components?

Q: What are the biggest challenges in scaling sustainable coating technologies from the lab to full commercial production?

The old adage says that a chain is only as strong as its weakest link, and the supply chain required to support commercialization of a sustainable coating is not exempt from this. Furthermore, for the product to be truly sustainable, each step of the process needs to be in itself sustainable.

It begins with raw materials sourcing and the aim to reduce dependency upon materials derived from fossil fuels. Can renewable biomaterials be used? Are they realistically available in sufficient industrial quantity? Can they be used in existing formulations, or does the incorporation require use of surfactants or additives or stabilizers—and are these from sustainable manufacture in themselves?

Now consider the energy requirements of formulation and large-scale production. Might any viscosity, dispersion, or stability issues drive energy consumption up? Or is there a need to manage heat transfer, either to maintain temperature to keep things flowing or remove it from an exothermic step in the process?

Are any byproducts or pollutants created in the process, surpassing explosion safety limits or allowed waste gas levels. Alas, the same rules apply for sustainable coatings as to scaling any production.

Q: How can collaboration across the value chain—raw material suppliers, formulators, applicators, and end users—accelerate progress toward shared sustainability goals?

Let’s look at three coatings: an interior, decorative house paint sold in Scandinavia; a metallic-effect, high-gloss automotive coating; and a high-performance durable protective coating on an oil rig in the North Atlantic Ocean. Our industry serves all three scenarios, but each one has a specific set of performance, application, pricing, and environmental requirements and targets. The willingness to become more sustainable might be there, but in each case the path to reaching those sustainability goals is going to be different. Those individual pain points, restrictions, and limitations need to be shared throughout the supply chain for us to truly make progress. It needs communication. And then it needs collaboration.

We are looking at a paradigm change in our industry, with innovation taking place all along the supply chain. We are seeing the introduction of new raw materials, the creation of new formulations, the introduction of more efficient production processes and easier application processes with less energy requirements and lower emissions, and the goal of non-harmful coatings that can either degrade or be recycled when a product reaches end-of-life.

It’s a big task and only possible with close collaboration. One part of the chain directly influences the next. If we acknowledge and respect that, we will become increasingly effective.

Wayne Daniell, Ph.D., joined The ChemQuest Group in 2023. Over his extensive career, Daniell has founded and managed companies that developed nanomaterials and various coatings additives for use in markets such as consumer electronics, renewable energy, and white biotechnology. Daniell holds a bachelor’s degree in chemistry from the University of Reading, as well as a doctorate in chemistry from the University of Nottingham. A UK native currently based in Germany, Daniell speaks English and German.

Waterborne coatings significantly reduce VOC emissions and improve air quality compared to traditional solvent-based systems. They offer strong performance, durability, and versatility across architectural, industrial, and automotive applications. CoatingsTech talks with Dr. James W. Rawlins from the University of Southern Mississippi about the future of waterborne coatings both in the industry and at the university level.

Q: What are the most recent noteworthy advancements in waterborne performance?

A: In the last few years, exterior-durable latex platforms enabled by reactive polymer-bound surfactants have been a consequential step forward. By copolymerizing reactive/polymerizable surfactants into the latex backbone, concerns associated with surfactant migration, water uptake, and sensitivity have been mitigated, which have historically been issues with waterborne films. Additionally, modern waterborne polyurethanes and polyurethane/acrylic hybrids are now becoming available from experimental/laboratory and commercial materials.

Q: Where is the next big leap likely to come from?

A: There is a lot of research activity happening right now. Innovations in dynamic covalent networks show near-urethane mechanical energy absorption methods, resulting in circularity, repairability, and potential recyclability, in addition to higher crosslink network control and tunable mechanical deformation processes. There is also significant work being done on designed stratification and hybrid lattices in PU-acrylic and silicone-acrylic systems.

In the short term, there is strong progress coming from advancements in additives. Reactive and anchored additives are particularly promising. Another strong area in additives is platelet barriers and rare-earth/organophosphate inhibitors, but the fastest acceleration is happening in testing and digital technology. New methods are being developed for early detection and quantification of failure before they become visible macroscopically.

Q: How can formulators meet sustainability targets without sacrificing durability?

A: In several ways. Water uptake could be reduced at the source by using reactive surfactants and polymer-bound stabilizers, and free, mobile surfactants could be avoided wherever possible. Crosslink density should be driven down with low volatile organic compound chemistry: driven mainly through carbodiimide, blocked-isocyanate, or self-crosslinking mechanisms in acrylic/polyurethane dispersion hybrids. Barriers could be built but understanding and quantifying water, electrolyte, and oxygen barrier differences for common chemistries is needed.

Q: How do university–industry collaborations accelerate innovation?

A: Learning is best achieved through immersion. The combination of total immersion and timeline-driven projects, which is something industry needs, with solid fundamentals such as scientific goals and objectives in an integrated team, drive real depth and real-knowledge gains through necessity. These combined teams are driven by student enthusiasm, industry support, and passionate scientist and engineering personnel with experience. Flagship consortia move students from working with the theoretical to the practical, with fundamental concepts moving into products, as well trained and developed students drive new paradigms.

Q: What excites you most about the future of waterborne coatings?

A: There are many. One is one-pass which are self-organizing films, stratifying hybrids, that can deliver stain resistance and direct-to-metal (DTM) corrosion without extra layers. Another important contribution is novel material compositions that are sustainable and circular, and dynamic networks enabling repairable, recyclable waterborne films with high chemical resistance. Lastly, data-driven developments such as AI data gathering for machine learning that is linked to accelerated tests in a context of real test results are beginning to remove blind spots for unquantified or poorly connected concepts and this improves upon our scientific rationale moving forward and shrinks lab-to-field translation cost and time.

James W. Rawlins is a professor of Polymer Science and Engineering at the University of Southern Mississippi, where he has directed an 11-member research group focused on Surface Coatings and Circular Materials since 2004. Rawlins, chairman of The Waterborne Symposium, has published 61 peer-reviewed articles and holds 17 U.S. and European patents. Earlier, he served as technical director at Highland International and held R&D and European technical marketing roles at Bayer (now Covestro) in Pittsburgh and Leverkusen.

Wood, by virtue of being a renewable material, and when sourced from responsibly managed forests, constitutes a sustainable and responsible building material. If continuously exposed to water, wind, and sunlight, though, wood substrates are subject to damage, manifested as discoloration, cracking, and decay. Protective coatings can delay or prevent damage, improving the durability and prolonging the life of this vital natural resource. There is a demand for wood coatings with low-volatile organic compound (VOC) content, a requirement often achieved with “VOC exempt” solvents.

Recognizing that the use of certain, widely used VOC exempt solvents may be permanently restricted in many applications because of proposed state-level environmental regulations—for example, by the South Coast Air Quality Management District in California as early as 2026— creative solutions to match VOC and performance targets are critical. A proprietary polymer has been developed that enables the replacement of these VOC exempt solvents with water. Using this unique technology, a low-VOC waterborne coating for exterior wood substrates has been formulated to provide exceptional protection, which meets or exceeds that of conventional wood coatings.

Introduction

As an exterior substrate, wood has both practical and aesthetic advantages. Not only does wood offer an organic, warm look, it readily accepts color, ranging from semi-transparent stains to fully opaque coatings. Notably, wood can act as a natural insulator. Wood substrates, therefore, are an attractive and environmentally sound alternative to brick, concrete and vinyl.

Wood substrates, however, can be an expensive option, because regular maintenance is required to prevent decay, damage from insects, and deterioration caused by weather. Wood is particularly susceptible to fluctuations in environmental moisture. Continuous high humidity and periodic severe and wet weather can result in warping, cracking, and rot, which, if not addressed by timely repairs, can lead to irreversible structural damage.^1,2

Protective coatings are therefore critical to maintaining exterior wood substrates. One such coating, spar varnish, is particularly effective. Spar varnish, also known as “marine varnish” or “yacht varnish,” was originally developed for use on the wooden poles that support the sails (“spars”) of sailing ships.³ Generally, a spar varnish is composed of an oil, like tung oil or linseed oil, which penetrates the substrate, and a resin, such as an alkyd or a polyurethane, which provides hardness. These components are solubilized in a compatible solvent, which contributes to ease of application. Spar varnishes are formulated to be flexible, allowing the coating to expand and contract in concert with changes occurring within the wood substrate, and water resistant, allowing the coating to provide a barrier to environmental moisture. Spar varnishes are also typically formulated with UV-absorbing compounds, which both extend the lifetime of the coating and prevent the substrate underneath from degrading.

As of 2023, the global market size for marine spar varnish was valued at approximately USD 1.2 billion. This market is projected to reach around USD 2.5 billion by 2032, growing at a compound annual growth rate (CAGR) of 7.5%.⁴ This growth is the result of increasing demand for protective coatings in marine applications and outdoor wood furniture, as well as increased awareness about the importance of safeguarding wooden structures against harsh environmental conditions.

Solvents typically used to formulate a spar varnish include mineral spirits, aliphatic hydrocarbon-based solvents, such as naphtha, and aromatic solvents, such as xylene. While the volatile organic compound (VOC) content can vary, VOC content for a standard spar varnish using traditional solvents usually ranges close to 475 g/L. The VOC limit for spar varnishes under the South Coast Air Quality Management District (SCAQMD) in California and the Ozone Transport Commission (OTC; Mid-Atlantic and Northeast) Model Rule 2010, however, is 275 g/L.^5,6 For a spar varnish to meet lower VOC requirements, “VOC exempt” solvents, such as parachlorobenzotrifluoride (PCBTF) or tert-butyl acetate (t-BAc), must be incorporated.

The U.S. Environmental Protection Agency (EPA) granted PCBTF and t-BAc exempt status because these solvents have negligible photochemical reactivity and do not significantly contribute to ground-level ozone formation.^7,8 PCBTF is the most widely used VOC exempt solvent in the coatings and adhesives industry. Another VOC exempt solvent, tert-butyl acetate, has been promoted as a potential replacement for the halogenated PCBTF. In 2022, however, the SCAQMD included a provision in Rule 1168 (Industrial Adhesives and Sealants) that prohibited the use of PCBTF and t-BAc.^9,10 The District intends to follow through with identical rulings for other coating rules, including Rule 1136 (Wood Products Coatings) as early as 2026.¹¹ Recognizing that the use of VOC exempt solvents may be permanently restricted in many applications, creative solutions to match VOC and performance targets are needed.

By Brian Vest, Lichang Zhou, Linda Adamson, and Celine Burel, Syensqo

Perfluoro-and polyfluorinated-alkyl substances (PFAS) have been widely used for a variety of applications, including water-resistant fabrics, nonstick cookware, stain-resistant carpets, firefighting foams, food packaging, and some personal care products. Their unique properties of resisting heat, oil, grease, and water make them highly versatile across various sectors. One type of these chemicals, fluorocarbon surfactants (FCS), has been used specifically in waterborne coatings for improving early “hot block” resistance. However, risk management and upcoming regulations are driving formulators to eliminate the use of these chemicals from their formulations. This has led to a balancing act for formulators as they try to move to more sustainable additives without sacrificing performance.

This study will cover the efforts made in our group for the use of novel phosphate ester wetting agents which deliver improved early hot block resistance without the adverse environmental concerns of fluorocarbon chemistry. These novel alkyl phenol ethoxylate (APE)-free and very low volatile organic compound (VOC) specialty additives deliver improved colloidal stability, which helps provide a combination of wetting, dispersing, and compatibility properties to the finished water-based coating. Data will highlight overall paint performance and touch upon structure/property relationships that lead to improved anti-blocking performance.

Introduction

Manufacturers of waterborne coatings are increasingly facing stringent regulatory requirements to transition towards environmentally sustainable formulations. These formulations must not only exhibit low volatile organic compound (VOC) levels but also eliminate hazardous substances such as alkyl phenol ethoxylates (APEs) and fluorocarbon surfactants (FCS). This regulatory landscape presents a formidable challenge for formulators who are tasked with integrating eco-friendly additives while maintaining the integrity and performance of the coatings.

FCS pose a particular challenge for formulators due to their distinctive molecular structure and the comprehensive balance of properties they impart to formulations. A critical performance attribute provided by FCS is early-stage—specifically, 1-day dry—hot block resistance. This property is essential in waterborne semi-gloss to gloss formulations designed for low-VOC applications. For decades, FCS have been instrumental in achieving this performance characteristic without adversely impacting other application properties. However, FCS belong to a broader category of chemicals known as perfluoroalkyl or polyfluoroalkyl substances (PFAS), which are classified as substances of very high concern (SVHC). PFAS are of significant health concern due to their persistent nature, as they do not readily degrade and can accumulate in the environment and in the human body over time, earning them the moniker “forever chemicals.”¹ Consequently, there is mounting regulatory pressure globally to identify safe and environmentally benign alternatives to fluorosurfactants across various industries.

In response to the demands within architectural coatings, an extensive study of alternative technologies was undertaken, with a concentrated emphasis on waterbased architectural coatings. This rigorous investigation identified that modifications to a specific phosphate ester chemistry could provide an effective solution, yielding superior early-stage hot block resistance while maintaining a comprehensive balance of application properties. This research culminated in the development of an innovative anti-blocking additive tailored for waterborne coatings.

Background

Block resistance is the capability of a paint when applied to two surfaces to not stick upon contact when pressure is applied under various temperature and humidity conditions. For example, good block resistance helps keep a door from sticking to the jamb or a window from sticking to its frame. When the two painted surfaces are pressed together, chain diffusion and entanglement occur from the mobile polymer chain ends, resulting in poor block resistance. Several factors can influence the blocking resistance of a formulation, such as the polymer T_g, the formulation space, and the type of surface-active additives being used. Figure 1 is a cartoon schematic demonstrating good and poor block resistance.

FIGURE 1 Cartoon schematic of block resistance.

FCS are commonly used to improve blocking resistance in waterborne formulations by providing a “protective layer” at the surface, thereby preventing the polymer-to-polymer entanglement (Figure 1). However, due to the environmental challenges and regulations of fluorocarbon chemistry, formulators need a new additive solution to improve block resistance. The scope of this project was to identify an additive that could be easily used by the formulator, either as a post-add to an emulsion or added directly into the formulation, which could match the block resistance performance of fluorosurfactant chemistry without the environmental concerns.

The main objective of this study is to generate formulating knowledge that can be applied for selecting appropriate solar reflective pigments and fillers for exterior wall coatings of various colors while retaining other important coating properties. A low pigment volume concentration (PVC), all acrylic, white formulation was used as the tint base for all colorants, conventional and infrared (IR) reflective. The key tests included rheology of the wet paints and color, gloss, hiding, and solar reflectance of dry coating films. Commercially available solar reflective materials, such as hollow spherical inorganic and organic particulate fillers and mixed-metal-oxide black and other color pigments and their equivalent conventional pigments were studied. Particular attention was focused on the issue of viscosity instability of tint base when tinted with colorants. Solar reflectance gains from IR-reflective pigments will be presented in comparison to coatings of the same color and other properties, formulated with conventional colorants. Results of this study can be used to estimate cooling energy savings due to incorporation of IR-reflective pigments.

Introduction

The earth receives about 50% of its solar power in the form of ultraviolet (UV) and visible radiation whereas the remaining 50% is in the form of infrared (IR).¹ The need for solar power to sustain all forms of life on earth is an unarguable fact. However, excessive amounts of solar power can cause harmful effects. An example of this is the phenomenon known as the heat-island effect.² Within a highly developed urban center, roofs and pavements receive and trap excessive amounts of solar energy in the form of heat causing greater needs for cooling the interiors of urban structures located in warm climatic regions. The need for cooling adds to the building maintenance cost, increases the building’s carbon footprint, and contributes to air pollution.

The above phenomena and issues have been well recognized for over four decades.³ To mitigate the problems associated with excessive solar heating, solar reflective and heat emission technologies have been developed and widely adapted for roofs and, to a significant extent, to pavements.^3-9 According to the Cool Roof Rating Council’s (CRRC) website,¹⁰ currently there are 3180 certified roof coating products. Due to the heightened awareness of global warming and ever-rising energy costs, there is a need to extend solar reflective technologies beyond roofs and pavements to other surfaces, such as exterior walls. According to a recent study by Lawrence Berkley National Laboratory’s Heat Island Group, there is great untapped potential for cool coatings for walls.¹¹ However, there are only a few solar reflective coating products for walls, and only 147 certified products are listed on the CRRC website. A literature survey has shown that, although there is increased research activity on heat-reflective coatings for walls, formulation data for commercially viable exterior wall coatings are very limited. The primary objective of this study is to contribute to filling this knowledge gap and enable formulators to develop their own successful products.

Initially, the study focused on understanding and quantifying the heat-reflective performance of conventional waterborne exterior architectural coatings and optimizing the formulations for solar reflectance without the use of specialty heat-reflective materials. All experimental coatings were prepared according to commercially viable formulations. In addition to solar reflectance, other key properties of the coatings, both at wet state and as dry films, were monitored. Results from these types of studies should enable formulators to select solar reflective grades of common raw materials while retaining other important coating properties. The solar reflective materials studied include hollow-spherical inorganic and organic particulate fillers and mixed-metal oxides.

The rheology modifiers used in all formulations in this study are associative thickeners that are sensitive to many formulation variables, including the colorants. As our previous studies have demonstrated,¹² this sensitivity used to be a huge problem causing unpredictable viscosity drops of tint bases when tinted with predispersed colorants. A secondary objective of the current study is to assess the magnitude of the associative thickener sensitivity to today’s colorants, both conventional and solar reflective.

Experimental Materials and Methods

All raw materials used in formulating the coatings are routinely used by the paint and coating industry and were obtained from commercial suppliers. The initial filler (calcium carbonate and nepheline syenite) evaluations were conducted with an exterior flat white formulation, at a pigment volume concentration (PVC) of 43.4 containing predispersed TiO2 and filler (Base Formulation 1 (BF1)). The next set of formulations was prepared with TiO2 in dry powder form (BF2). An example of the latter type, 25 PVC formulation, is shown in Table 1. Our most recent experiments were conducted with a 17.5 PVC, direct-to-metal (DTM) formulation identical to a published study.¹³ Formulations were mixed with an EMI MXML-STD disperser using a Cowles type blade in pint-sized paint cans at approximately 400 g total weight. The grind step was conducted at 1600 rpm and the let-down step at 1000 rpm.

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Introduction

In this article, we introduce a new applied method, brush workability, for determining the open time of architectural coatings, that offers good reproducibility and high level of differentiation in lab testing. This method shows validated correlation to real world application, using a selection of commercial paints in a double-blind contractor study.

Open time in architectural coatings is defined as the time after applying a single coat of paint where the film remains wet and workable. It is distinct from the full cure time or time before a second coat may be applied. Poor open time is evidenced by the inability to smoothly blend two areas of coating on a large substrate (within a single coat) and is also correlated to poor leveling as the film dries which can result in brush marks or visible roller pattern. Open time can also be evident during the coating application, where paints with poor open time may exhibit roller picking and poor drag between the drying film and the brush or roller.

There are multiple stages in paint drying, including: (1) Diffusion of water through the coating to the air interface and evaporation; (2) Film compaction and particle jamming; (3) Latex particle deformation under capillary force; final evaporation of water; and (4) Final cure/film compaction and coalescence via polymer entanglement. ^1-3 Workable open time is defined by the first two stages.

Current industry standards for measuring open time include ASTM methods such as wet edge,⁴ dry to touch (DTT),⁵ and use of automated dry time recorders.¹ These methods may be subjective in the ways they are rated and/or applied. Furthermore, many scientists and customers have noted that such methods do not translate well to actual paint application and/or are not physically representative of practical workable open time. This underscores the need for better methods with reduced subjectivity and better correlation to real world application, such as our new method.

Materials and Methods

Table 1 details the commercial paints used in this study, with information on technical properties. All paints are eggshell sheen, interior paints. Paint viscosities were measured using the lab viscometers (KU Stormer, ICI, Brookfield LV3/6 rpm). All testing was performed blind, using the paint IDs in Table 1 such that the applicator did not know which commercial paint was being tested. All lab open time tests were performed in a temperature-controlled lab at 75 °F and 50% RH.

Wet Edge: The wet edge test is adapted from ASTM D7488, using two vertical parallel lines running the length of the chart rather than six independent X marks at each time point. Paint was drawn down on a Leneta BK chart using a square bar with 5-mil gap. Immediately following the drawdown, the timer was started and two lines were drawn down the center of the wet film using two parallel tongue depressors. At 1-min intervals, the wet film was brushed over with 15 brush strokes in one direction. The brush was not dipped in fresh paint each time, ensuring a harsher, quicker test. The wet edge open time is the last time when the vertical lines are not able to be seen.

Dry to Touch (DTT): DTT testing was performed using 3 mil drawdowns on BK charts. Following the drawdown, a gloved fingertip was placed in the center of the wet drawdown at 1-min time intervals, and then the wet fingertip was pressed on the chart outside the drawdown area to leave a fingerprint. The paint is considered dry to touch when no finger mark is left. This method is adapted from ASTM D1640.5

Automated Dry Time Measurements: A Gardco circular path dry time recorder was also used for automated drying time measurements of paints. The machine consists of a Teflon ball stylus with a weight on the arm to control force, which moves in a circle through the wet film at a set speed. Tests were done using the 1-h setting, and 5-mil drawdowns on BK charts. The stylus was set approximately in the middle/center of the drawdown. Once complete and dry, the dry path was inspected for four types of signatures according to ASTM procedure D5895.1 There is a transparent overlay to mark the time points corresponding to the positions of each signature.

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