µţ˛âĚýMichelle Gallagher,ĚýTyler Weiss,ĚýPaul Doll,ĚýDan Fonseca, andĚýErica Frankel, Dow

The drive towards sustainability and a more circular economy has become a pivotal strategy across the coatings industry. This shift has spurred initiatives to reduce carbon footprint emissions, utilize materials with extended lifespans, source from renewable feedstocks, and create safer products. In response, the first all-acrylic bio-based latex emulsion polymer tailored for the North American interior paint market has been developed. This next-generation commercial polymer offers numerous advantages over traditional fossil feedstock-based emulsions, including a competitive cost structure, bio-based carbon content exceeding 20%, and exceptionally low volatile organic compound (VOC) levels, all while maintaining performance characteristics associated with acrylic paints.

Beyond addressing bulk VOC concerns, the industry has seen increased scrutiny over the past decade regarding paint emissions post-application. This article explores seminal methodologies and volatile emission results of paints formulated with latexes derived from various feedstocks. It highlights the ultra-low emissions achieved with this new bio-acrylic polymer, representing a significant advancement toward more sustainable interior paint.

Introduction

The global coatings industry is undergoing a pivotal transformation, shifting from fossil- derived raw materials to more sustainable, renewable alternatives. This change is driven by the need to foster a more circular economy, minimize environmental impacts, reduce greenhouse gas emissions, and align with ever-changing health and regulatory standards.¹

However, this movement is not the first paradigm shift the coatings industry has undergone as lowering the total VOC in wet paints has been a continued concern for raw material suppliers and paint manufacturers for several decades. In the 1940s, solventborne paints contained VOCs in concentrations as high as 700 g/L.²ĚýWith the emergence of latex paint in the 1950s, VOC was greatly reduced. Since that time, the Clean Air Act and the Clean Air Act Amendment have helped push that total VOC even lower.³ĚýAgencies such as the California Air Resource Board (CARB) and certifications such as Blue Angel have led the paint industry toward near-zero VOC regimes. More recently, there has been growing concern and emphasis on indoor air quality (IAQ) and VOC emissions as paint dries over time. Measuring IAQ accurately is a complex challenge, and it has taken decades to develop the equipment, procedures, and expertise to collect, measure, and identify potential sources that can lead to poor IAQ.⁴ĚýWith a growing list of standards such as UL Green Guard⁵Ěýand California Department of Public Health (CHPD) 01350,⁶Ěýnew innovations within the paint industry such as the transition away from fossil feedstock-derived materials will need to also uphold the increasingly stringent standards surrounding VOC and VOC emissions.

At its core, adopting bio-based coatings lies in their potential to reduce dependency on fossil resources and lower overall carbon footprints. Traditional coatings rely on fossil-based feedstocks and additives, which are increasingly scrutinized for their environmental and health impacts. Transitioning to renewable feedstocks can directly support greenhouse gas reduction strategies and respond to consumer and regulatory demands for safer, more sustainable materials that can be validated by third-party certifications.

Among the most promising advances is the development of bio-based acrylic polymer dispersions capable of matching, and in some cases surpassing, the dry-film performance of traditional fossil feedstock-based systems while also exhibiting superiority in low emissions. A newly developed bio-based acrylic binder represents a milestone in this journey. Beyond merely substituting fossil fuel inputs, the binder incorporates traceable biocarbon content into polymer emulsions, verified by established methodologies, and it delivers on three key sustainability goals:

• substantially reduced bulk and emitted VOCs compared to fossil feedstock-based control paints
• absence of intentionally added per- and polyfluoroalkyl substances (PFAS) or alkylphenol ethoxylates (APEO)
• approximately 27% bio-based carbon that can enable the U.S. Department of Agriculture (USDA) BioPreferred^®Ěýcertification of interior latex paints

This article presents a detailed technical evaluation of the new all-acrylic bio-based latex binder. This innovative dispersion not only preserves formulating latitude and dry-film performance but also achieves dramatically reduced levels of VOC emissions, both in bulk and during application, relative to standard fossil-based controls. The findings are grounded in comprehensive data which are provided in this article.

Experimental

Preparation of Bio-Based Paints

Paints with the new bio-based binder were made into both flat and semi-gloss formulations (seeĚýTables 1Ěý˛ą˛Ô»ĺĚý2). The starting point flat white formulation comprises 37% volume solids and 48% pigment volume concentration (PVC), while the semi-gloss formulation consists of 37% volume solids and 24% PVC.

Additionally, thickened binders of equivalent weight percent solids were made to determine emitted VOC contributions from just the binder versus those from the total paint formulation. The thickened binders were made by diluting with the appropriate amount of water and then modifying their rheology with an inorganic thickener which enables appropriate coat weights to be achieved without contributing to emitted VOCs.

Continue reading in the March-AprilĚýissue of CoatingsTech

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.”¹ĚýSustainable 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.”²ĚýSolutions 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 2023.³ĚýAdditionally, 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.⁴ĚýAs 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.^1-4ĚýThe chemistry for these networks typically involves urethane, urea, ether, and thioether chemistries.^5-7ĚýAmong 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.^8,9ĚýThe most common way to form polyurethane networks requires the use of hazardous isocyanates.⁸ĚýHowever, 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.^12-16ĚýFor 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.^21,22ĚýPolyurethane networks are not necessarily hydrophobic and often rely upon incorporation of other materials and segments to make hydrophobic material.²³ĚýThe 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^24-27Ěýand cyclic carbonate chemistry.^28-30ĚýThe 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.

In the simplest terms, sustainability could be defined as less waste and more efficiency. This could mean fewer processing steps, the use of fewer chemicals or other building blocks, or the ability to develop products that last hundreds of years without the need for constant maintenance.

In the coatings (paint) world, sustainability is usually looked at through the lens of fewer chemicals, biomaterial substitutions, shortened or fewer manufacturing steps, or outright chemical bans. Significant efforts are currently underway to reduce petroleum-based materials in the first place along with trying to make the new products last at least as long as their predecessors.

There is another way to look at materials sustainability. What if the pretreatment chemicals and coatings could be eliminated altogether? What if the oxide was also the color coat? What if the longevity of stainless steel could be exploited together with its oxidation potential? What if color could be imparted onto stainless steel strip using only one production operation for both steelmaking and coloring? What if these innovative ideas were actually more cost effective?

First Steps

In 1971, Allegheny Ludlum Steel Corporation took a step in that direction. While certainly not under the guise of sustainability, the company developed a process that produced black stainless steel for use in formed architectural products.¹ In this case, a stainless steel strip was produced by oxidizing the stainless surface to form a porous oxide coating and impregnating it with an alkali metal silicate, and then drying and fusing the silicate by heating between 1400 and 1600 °F. Temper rolling the finished product—a typical steel finishing process—allowed for flattening the strip to facilitate fabrication.

This process was an efficiency improvement over the original pre-1968 process where many more production steps were used. First, the strip was treated to obtain a black oxide and then coated with a water-soluble alkali metal silicate or a water-based thickened or gelled solution of sodium or potassium dichromate. The next step involved removing the water and subsequently heating the coated surfaces to a temperature high enough to form a uniform, black, porous oxide 1,000–500,000 Å thick. Excess coating and loose oxide were then scrubbed off with water.

In addition to reducing the number of processing steps, the 1971 process eliminated many quality problems. There was better thickness uniformity, less visibility of any spray or rolling pattern, good aesthetics, and better condensing humidity resistance, as depicted by the absence of white residue all over the strip. Steam testing, abrasion resistance, chemical resistance, mandrel bend, and impact testing were also improved to the point that this black stainless could be formed into tubes or building panels with decent aesthetics. With better oxide thickness control, color was also more uniform.

Fast Forward to 2013

Over the 40 years since the first steps in manufacturing blackened stainless, many material inventions and improvements have occurred. Stainless steel itself has become a more uniform product, with improved surface finishes that can now be used in a variety of aesthetic-critical applications. Base metal chemistry modifications and more controlled annealing atmospheres and temperatures have led to increased formability as well.

Alongside steel production maturation, the advent of affordable, usable nanotechnology opened a huge window for surface modification. Nanoparticle surface treatments were developed to reduce damaging oxidation and corrosion of stainless steel and other alloy components in oxidating and corrosive conditions.²

Improving the longevity of stainless steel at elevated temperatures was the genesis of this development. Power generation plants often have problems with damaging oxidation from accelerated high-temperature fire-side corrosion due to molten alkali salts. Other problems include accelerated medium-temperature fire-side corrosion due to low oxygen activity environments and the presence of sulfur and steam side oxidation of tubing, piping, and valves in fossil fuel-fired boilers.

Pressure has been placed on power plants to increase efficiency, meet stringent environmental regulations, and ensure plant reliability, availability, and maintainability—ideally while minimizing costs.³

Some of the nanoparticles used as surface treatments for corrosion and oxidation resistance include aluminum, silicon, scandium, titanium, yttrium, zirconium, niobium, lanthanum, hafnium, tantalum cerium oxide (nanoceria), and thorium. These nanoparticles do not really form coatings but rather are doping agents that become embedded within the oxide structure.

Over time, yttrium has become a preferred nanoparticle for these types of applications. Yttrium, particularly in the form of yttrium oxide nanoparticles (Y2O3 NPs), is considered superior because of its exceptional properties around high thermal stability, strong chemical stability, mechanical strength, and strong corrosion resistance. Perhaps the greatest attribute under the veil of sustainability is that yttrium has low toxicity. Because of its low toxicity, this nanoparticle is often used in biomedical applications.

Minimox® is one of the yttrium-based, self-protective alloy treatments that minimizes oxidation of alloys at elevated temperature. It changes the structure and/or chemistry of the thermal oxide, which becomes denser and more adherent than thermal oxide without Minimox® doping. Flaking, protrusions, and microvoids are eliminated, resulting in a smooth, dense, adherent surface.⁴

Depending upon the time and temperature of the annealing process, thin film oxides can be grown to thicknesses between 500 and 9,000 Ă… (1 Ă… = 0.1 nanometer). Oxidized surfaces doped with yttrium are characterized by excellent cyclic and isothermal oxidation, corrosion resistance in severe environments, and high resistance to severe heat and chemical environments. As a bonus, the thickness of the oxide can be controlled within a high-temperature annealing atmosphere to purposefully impart color onto a metal surface.

Modern Colored Steel

The black stainless steel for architectural applications referenced earlier in this article did not result in large volumes of product released into the field. Despite the excellent properties derived from the surface modification, stainless steel was too expensive for run-of-the-mill building applications. However, the idea of a black surface that did not require painting simmered in the background for many years. The thought of being able to colorize a surface using existing in-line annealing practices was a tantalizing thought. Black stainless manufactured using the existing in-line annealing process, without the addition of either paint or doping agents, was successfully accomplished in 2018.⁵ However, stainless remained an extremely expensive substrate for many applications.

It was determined that other substrates that were more in line with cost constraints of industries, such as appliance and automotive, would also benefit from this oxide modification methodology. Electrogalvanized steel (EG) was textured to the required product finish and the zinc coating was subsequently annealed. The resulting black substrate met all the requirements of appliance finish specifications for refrigerator door applications (the most stringent requirements in the appliance world). This “faux stainless” EG product was compared to black polished stainless and the GE Black PVD standard, and it was found to meet all requirements, including color (Figure 1), gloss, stain/aging, anti-fingerprinting, corrosion resistance, and mechanical properties—all at a much lower cost.

FIGURE 1 Black color comparison between standard product, black stainless steel and “faux stainless steel” textured electrogalvanized.

Finally, in 2023, a method of colorizing stainless steel using yttrium doping and annealing was developed. To prove the concept, stainless steel coils were coated with an aqueous yttrium pretreatment solution and batch annealed for several hours to oxidize the surface. Batch annealing is not particularly uniform, and is not the streamlined process of choice, but enough of the coil exhibited the required properties to move forward and optimize the process.

The basic idea was to dope the surface with an aqueous yttrium nano-solution using an in-line roll coater, followed by continuously annealing the strip while varying time and/or temperature in the annealing furnace to grow the oxide and obtain the desired color.⁶ Even keeping the annealing furnace atmosphere constant, varying line speeds (time in anneal) can allow for the efficient production of different colors. (See Table 1.) These colored stainless coils were fabricated and placed on structures in the Nashville, TN, area (Figure 2) and are still in place today.

FIGURE 2 Colored stainless panels on structures in the Nashville, TN, area.

All the aforementioned work has culminated in less waste and more efficiency. Technological improvements in substrate quality, steel processing, and nanotechnology have bolstered the development of a variety of products previously deemed impossible, too expensive, or of insufficient quality for commercial production. By looking at outside-the-box alternatives, it is possible to obtain color by manipulating the oxide and removing the organic coating completely.

References

1. Helgert, Harold. L; et.al. Method of Making Black Stainless Steel Sheet. U.S. Patent 3,556,871, January 19, 1971.
2. Kerber, Susan J. Nanoparticle Surface Treatment. U.S. Patent 8,568,538 B2.
3. Stott, F. H. Influence of Alloy Additions on Oxidation. Materials Science Tech. 1989, 5 (8), 734.
4. Material Interface Inc. Protecting Furnace Components with Minimox® Alloy Treatment. Minimox® Product Data Bulletin. 2016.
5. Myers, F.A. Black Steel. AK Steel Presentation, 2018.
6. Myers, F. A.; Price, L. R. Method of Colorizing Stainless Steel Using Strip Anneal Processing. U.S. Patent 11,584,997 B2, February 21, 2023.

Cynthia A. Gosselin, Ph.D.,Ěýis director at The ChemQuest Group,Ěýwww.chemquest.com. Email:Ěýcgosselin@chemquest.com.

Unbeknownst to many, microplastics do not originate solely in the ocean. In fact, most microplastic accumulation primarily occurs on land and then moves to the waterways. Oceans have been polluted between 83,000 to 236,000 tons of microplastics yearly. Agricultural soils of all kinds, including agricultural soils, have 107,000 to 730,000 tons of microplastics dumped into the soil each year through processed sewage, mulches, slow-release fertilizers, and even seed coatings.¹

During the last few years, there have been ongoing discussions about what defines a microplastic. Microplastics are plastic particles ranging in size from 5 mm to 1 nm. Primary microplastics are intentionally manufactured in smaller sizes for use in consumer cosmetics and biomedical products. Secondary microplastics are plastic waste particles that break down from larger plastic materials. Secondary microplastics brought about by degradation of larger discarded plastics are the subject of this article.

Only 1% of total microplastics are due to seed coatings.² However, with a rather forceful kick from the European Chemicals Agency (ECHA), seed manufacturers are being required to eliminate microplastics that are generated due to seed coatings by October 2028. The rest of the world is not far behind. In fact, France has pulled implementation ahead to January 1, 2027. California has already proposed legislation that would eliminate 75% of plastic waste by 2030. While this does not yet affect seed coatings, history suggests that a broader set of regulations will germinate from this legislation.

Certain seed coatings are exempt from the October 2028 regulation:³
• Liquids: Must not form films upon drying.
• Natural origin coatings: No chemical modifications allowed. Even the simplest chemical modification might cause eventual microplastic formation. Commercially used natural polymers can contain additives, processing aids, or impurities that could hinder biodegradation or contribute to microplastic pollution.
• Water soluble coatings: Must have a solubility of ≤ 2 g/l.
• Biodegradable: Not to be confused with compostable materials.
• Coatings with no carbon atoms in the molecular chain structure

Manufacturers have embraced the challenge of eliminating microplastics from seed coatings. Even though seed coatings are 1% of the problem, producers across the globe are determined to become ZERO percent contributors to microplastic pollution.

The first step has been to make the microplastic coating fragments that detach from seeds as biodegradable as possible. Degradation rates vary, and no standard has yet been set. The lowest degradation rate so far is ≤ 48 days obtained from some commercially available polymeric coating mixtures. Biodegradable plastic formulations degraded completely in 32 days. Coatings selectively doped with certain plant growth promoting bacterium (Bacillus subtilis) degraded in ≤24 days.⁴ A good start, but still not enough.

A Seed Coating Primer

The first question in eliminating a problem material is to determine whether the material is really needed. Seed coatings are critically important for:
• Promoting germination and robust growth
• Providing resistance to pests and fungal infections
• Improving drought tolerance through osmopriming⁵ (for germination in low-moisture soils)
• Facilitating mechanical planting
• Increasing overall yield

While there are significant advantages for coated seeds (higher germination percentage, healthier roots and shoots as well as stronger established plants), there are also disadvantages (limited shelf life of treated seed, pesticide breakdown, incomplete crop protection, and surplus cannot be repurposed for grain). However, when weighing the risks, the ability to feed the world trumps any disadvantage. Eliminating seed coatings is not practical, so improvements to guard against microplastic formation and pollution must be the conclusion.

There are three basic methods of seed protection: film coating, encrustation, and seed pelleting.⁶

Film coating involves applying thin layers of coating solution (a total of less than 10% seed weight) onto the seed surface (Figure 1). For precise control over thickness and composition, a rotating drum or fluidized bed apparatus is used. Film coating allows the seed to maintain the original size and shape. In addition to resistance to environmental stressors, these seeds are well suited for mechanical planting and precision field applications.

FIGURE 1. Schematic of various protective film coating layers applied to seeds.⁷

Seed encrusting forms a protective matrix around seeds that is 100–500% seed weight. This allows for targeted delivery and sustained release of active ingredients throughout germination and early growth for pest and disease resistance, even in adverse soil conditions. A film is not formed. Many organic farmers take advantage of seeds treated with this technique.

Pelleting agglomerates seeds into uniform spherical pellets by coating them with a mixture of binding agents and additives that is >500% seed weight. This technique is especially good for small seed crops and precision planting. The enhanced seed-to-soil contact leads to good moisture retention, better germination rates, and uniform stand establishment.

Commercial Seed Film Coating Materials

Traditional seed film coatings are manufactured from polyethylene glycol (PEG), polyvinyl alcohol (PVOH) or chitosan (a glucosamine polymer).

Polyethylene Glycol is effective for improving seed germination and seedling establishment of sorghum under adverse moisture conditions. Osmopriming strengthens the antioxidant system further by increasing the osmotic adjustment of the seed resulting in increased stress tolerance.⁸

Lignan-modified PEG has a high molecular weight, takes a little longer to dissolve, and is less easily converted into water. The high-viscosity solutions do not transport oxygen, leading to no absorption by the seed, eliminating genetic or physical damage. Coating with 5-lignin PEG improved the germination percentage of maize seeds from 86.6% to 93.3%.⁹

Polyvinyl alcohol seed film coatings are extremely useful because water solubility and mechanical strength can be controlled. These coatings are used as a binder for adhering layers to the seed surface. Seed physical properties are improved and the delivery of active ingredients can be controlled. PVOH coatings decrease dusting and improve germination.¹⁰

Chitosan is one of the truly natural seed treatments and growth enhancers. This glucosamine polymer is developed from a sugar that comes from the outer skeleton of shellfish like crab, lobster, and shrimp. The material bonds to seeds via hydrophobic or cation-Ď€ interaction. Chitosan is a cationic source in an aqueous solution. Free amine groups form crosslinked polymer networks with dicarboxylic acids to improve mechanical properties.¹¹

Unlike other polymeric materials used for film seed coatings, Chitosan influences the biochemistry and molecular biology of the plant cell. The targeted plasma membrane and nuclear chromatin causes changes in cell membranes, chromatin, DNA, calcium, MAP kinase, oxidative burst, reactive oxygen species, cellulose pathogenesis-related genes, and phytoalexins. It is an ecofriendly biopesticide that boosts the innate ability of plants to fight fungal infections.¹² In addition, it allows for an innate immunity response in developing roots that destroys parasitic cyst nematodes without harming beneficial nematodes and organisms.

The Future

Sometimes the additives used in current seed coating formulations can lead to microplastic free products. Acting as rheology modifiers, film formers, and stabilizers, these biodegradable materials help to create porous films and coatings, enabling early seed germination.

One example is a microfibrillated cellulose viscous material that under high shear can be sprayed onto seeds. Under high shear, the fibrils break apart, lowering viscosity and allowing for consistent coating. After application, when high-shear conditions are removed, the fibrils reconnect forming solid films while still allowing for complete drying of the coating. These additives assist with germination, reducing or eliminating seed dusting and enabling longer shelf-life stability of liquid formulations.¹³

Seed coatings themselves are undergoing a metamorphosis as well. Petroleum-based polymers cannot always be made biodegradable and, at the same time, fully functional. The ideal would be to develop completely natural coatings that leave no residue, disappear without a trace, and retain critical seed protection and nutrient properties. Supramolecular engineered proteins have been developed over the past 15 years. They perform as well as synthetic polymer-based coatings but decompose naturally. This serves two purposes: mitigating soil degradation and eliminating microplastic pollution in farm fields.¹⁴

Thinking even further outside the box, these supramolecular engineered proteins might be the foundation for producing plant-based protein products to replace traditional single-use and even multiple-use carbon-chain plastics without the threat of microplastic pollution.

References

1. Petersen, K. S. There is an Alarming Amount of Microplastics in Farm Soil–and Our Food Supply. Environmental Health News. January 27, 2021.
2. Nielson, A.. The Seed Sector’s Battle Against Microplastics. Seed World. April 29, 2024
3. Verney, C.; DeGassert, G. Microplastic Seet Coatings the Perform Better than Conventional Ones: Myth or Reality? Agropages AgNews. June 14, 2024.
4. Accinelli, C. et al. Degradation of Microplastic Seed Film-Coating Fragments in Soil. Chemosphere. V 226. July 29, 2019. Pages 645-650.
5. Harish, D., et al. Effect of hydropriming and Osmopriming on the Germination of Seedling Vigor in East Indian Sandalwood (Santalum album L.). Forests. V 14, P. 1076. 2023.
6. Sharma, S. Enhanced Crop Potential: Exploring Seed Coating Techniques and Applications. LinkedIn. May 14, 2024.
7. King Quenson Group. A Farmer Friendly Technique for Producing Crops. King Quenson News. September 3, 2023.
8. Zang, Fei, et al. Seed Priming with PEG Induces Physiological Changes in Sorghum Seedling Under Suboptimal Soil Moisture Environments. National Institute of Health. October 15, 2015.
9. Yahong, G., et al. Preparation of Lignin Polyethylene Glycol Film-Forming Agent and Its Application in Chlorantraniliprole 5% Flowable Concentrate for Seed Coating. Industrial Crops and Products. V. 182. P 114877. August 2022.
10. Agriculture | Coating for Seeds, Fertilizers & FilmsPolyvinyl Alcohol. https://www.kuraray-poval.com/applications/agriculture (accessed September 10, 2024).
11. Chitosan. https://en.wikipedia.org/wiki/Chitosan (accessed September 10, 2024).
12. Hadwiger, L. A. Multiple Effects of Chitosan on Plant Systems: Solid Science or Hype. Plant Science. V. 208, 42-49. July 2013.
13. Electrolyte Tolerant Film Forming Agent for Seed Coatings. Borregaard https://www.borregaard.com/markets/agriculture/applications/seed-coating/products/film-forming-agent/ (accessed September 10, 2024).
14. Natural Alternatives to Microplastics Developed for the Seed Coating Industry. Environment Times. February 1, 2022. https://www.environmenttimes.co.uk/news/item/995-natural-alternatives-to-microplastics-developed-for-seed-coating-industry (accessed September 10, 2024).

By Kateryna Rudich, Yehor Polunin, Ayda Dadras, Mohiuddin Quadir, and Andriy Voronov

Introduction

The use of polymers as a seed coating is a prevalent agricultural practice because it helps to reduce the overall amount of chemicals needed, promoting more sustainable farming practices. Seed coating is the process of applying a protective layer, typically made of polymers, nutrients, or agrochemicals, to seeds before planting. The primary purposes of seed coatings are to enhance seed performance, protect against pathogens and pests, improve germination rates, and provide essential nutrients during early plant development, all while minimizing the risks associated with conventional seed treatment methods.¹ However, seed coatings mainly involve the use of petroleum-based, non-biodegradable polymers that significantly contribute to microplastic pollution.

This study explores the potential of biomass- and plant oil-based polymers recently developed by our group as a sustainable alternative to be applied in seed coatings. The resulting polymer, consisting of hemicellulose xylan modified by grafted chains made of babassu oil-based monomers (HX-g-BOBM), is designed as a sustainable film-forming material targeting advanced water barrier performance.² HX-g-BOBM is a highly biobased, tough, and processable bioplastic. Being biodegradable, it may offer a renewable alternative to applications of conventional petroleum-based polymers in food packaging. This study evaluates the feasibility of HX-g-BOBM as a seed coating by applying it to corn (Zea mays) seeds and assessing the effect on the seeds’ vigor and viability.

HX-g-BOBM Synthesis

Agricultural wastes such as some lignocellulosic materials and plant oils are excellent renewable resources for the production of sustainable coatings due to their chemical versatility, availability, and often low cost.3-6 HX-g-BOBM is synthesized from hemicellulose xylan and babassu oil, which are believed to be inherently biodegradable or compostable by nature. Babassu oil-based monomer (BOBM) and HX-g-BOBM were synthesized following the procedures described in earlier publications.^1,7,8 The structure of BBM is shown in Figure 1A. A schematic representation of HX-g-BOBM synthesis is presented in Figure 1B. Before polymerization, xylan was reacted with maleic anhydride through an esterification reaction. During this process, an ester bond is formed between the maleic anhydride and hydroxyl groups of xylan, while the vinyl group of maleic anhydride remains intact, providing a reactive site for the attachment of BOBM-based grafted chains. After successful maleinization, the modified xylan was added to the BOBM along with the AIBN initiator (1.5 wt %). Grafting polymerization reaction was conducted in bulk at 80 °C for 8 hours under a nitrogen atmosphere. After purification from unreacted xylan and BOBM, a homogeneous solution of highly branched HX-g-BOBM was obtained. Multiple xylan macromolecules are decorated by BOBM chains, and BOBM homopolymer is also present in the resulting material.

FIGURE 1 The chemical structure of babassu oil-based monomer (BOBM) used in this study. R (x:y) – the structure of the fatty acids (x – the number of carbon atoms in the fatty acid chain, y – the number of double bonds in the fatty acid) (A). Synthetic scheme of HX-g-BOBM grafted polymerization (B).

HX-g-BOBM Emulsification

To simulate an industrial approach, where seeds are typically covered by spraying a water-based slurry containing polymers and additives over the seeds in a rotating drum machine, HX-g-BOBM was emulsified in water. Dodecylbenzenesulfonic acid, which serves as an emulsifying agent, was first dissolved in water, vortexed for 5 min, and ultrasonicated for 20 min. The HX-g-BOBM dispersion was then added dropwise and was vortexed for an additional 5 min and ultrasonicated for 20 min until a stable emulsion with a final polymer content of 15 wt % was achieved. Particle size measurement was conducted using a Malvern Zetasizer Nano-ZS90 (Figure 2A).

The viscosity of the emulsion was measured using an ARES G2 rheometer with 25 mm parallel plate clamps, gap size 0.5 mm, strain 1%, frequency range 1-500 rad/s, and temperature 25 ÂşC. The viscosity of the HX-g-BOBM emulsion exhibits non-Newtonian behavior, with apparent viscosity decreasing as the shear rate increases, indicating shear-thinning behavior. At low shear rates (< 1 rad/s), the emulsion displays high viscosity, suggesting good stability and minimal settling of particles. The apparent viscosity decreased significantly at higher shear rates (> 10 rad/s), indicating that the emulsion would flow more easily during the seed coating process, which is beneficial for uniform coating application in industrial applications (Figure 2B).

FIGURE 2 Particle size (A) and rheological behavior (B) of 15 wt % HX-g-BOBM water emulsion.

Seed Coating Procedure

Seeds were coated manually using a plastic bag with a subsequent transfer of seeds to the sieve and drying at room temperature (25 ±1°C) for 24 hours. In each case, 100 corn seeds were incubated with 2 ml of water-based polymer slurry and manually shaken for 5 minutes to simulate the industrial rotating drum coating procedure. The weight of the seeds was compared before and after the coating procedure. The average weight increase was found to be 2.0 ± 0.3 wt % from the initial mass of seeds.

HX-g-BOBM Coating Water Absorption

The water absorption test was conducted to evaluate the coating’s interactions with water. Coating film samples were submerged in 20 ml of distilled water and kept at room temperature. After immersion, excess water was removed, and the samples were weighed at specific time intervals to quantify the changes in mass. To ensure accuracy and reliability, each test was performed in triplicate. The resulting plot shows the relationship between time and weight gain (Figure 3A). The ability of the coating to swell is advantageous for enhancing water retention, by helping to keep the seeds hydrated after planting.