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.^1-3ĚýThe 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.^4-7ĚýIn 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.¹⁰ĚýThe 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.¹²ĚýHowever, 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.^13,14ĚýFor 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.^15,16ĚýHowever, 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.

This research investigates the effects of whey protein coating on the chemical, bacterial, and sensory properties, proximate analysis, and shelf life of common kilka during frozen storage.

For this experiment, common kilka were coated with 9% whey protein while non-coated kilka were used as a control sample. Both the coated and non-coated samples were stored at -18 oC for six months. Results showed that total bacterial counts (1.47–2.49 log CFU/g) and Staphylococcus bacteria (1.02–1.71 log CFU/g) were lower in the coated samples compared to the control samples (P > 0.05). Coliform, E. coli, and Pseudomonas bacterial contamination were undetectable in both the coated and control samples throughout the storage period. Humidity (73.92–46.18%), protein (18.24–19.07%), lipid (4.27–4.01%), ash (1.82–2.12%), and calorie (108.85–120.78 kcal/kg) were higher in the test samples compared to the control samples. Values for peroxide (0.15–5.12 meq/kgoil), free fatty acids (1.32–12.40 g/100), thiobarbituric acid (0.14–0.98 mg/kg), total volatile basic nitrogen (TVB-N) (6.32-21.79 mg/100g), and pH (6.32-7.45) were lower in the test samples.

Significant decreases in chemical factors were observed in the coated samples compared to the control samples (p<0.05). The overall acceptance score had a better quality in the coated samples (80) compared to the control samples (113) (p<0.05). According to the results of experiments and statistical analysis, the coated samples had a favorable quality until the end of the storage period but the control samples had lost their quality. Therefore, a 9% whey protein coating is recommended for kilka fish as a better alternative to using disposable packaging dishes with a cellophane coating.

Introduction

Kilka fish belong to the genus Clupeonella, in the family Clupeidae. These fish are composed of three species consisting of Clupeonalla delicatula, C. engrauliformis, and C. grimmi (Coad, 2017). They can be processed into salted, smoked, pickled conserved, dried, and frozen fish. In Iran, kilka products are sold fresh, canned, or in frozen packaging. From 2016 to 2021, the annual catch ranged from 20,138 to 22,429 tons. Approximately 10-12% of this catch was used for human consumption, and the remaining 88-90% was used for animal feeds. 6,307 – 6,626 tons of the fish were caught in the Guilan Province, of which 5-12% was used for human consumption and the remaining 88-95% for animal feeds (Program and Budget Office, 2022). Consumption of fresh kilka fish dropped from 6% to 2.20% during the period of 2004 to 2009. Consumption of canned kilka also dropped during the same period, whereas consumption of frozen kilka rose during the same years (Seifzadeh, 2014). The frozen fish packs had a much higher sales rate in comparison to the sales of fresh fish because of their longer storage time and wider distribution. Sales of frozen fish were also higher. The fish packs were frozen for less than three months because longer frozen-storage time may lead to color changes, surface dryness, and peroxide accumulation. Even so, the first indication of a decline in quality after only one month of frozen storage was a reduction in the weight of frozen packed fish, which in turn had a deteriorating effect on the texture and taste of the small-sized fish. There was a 3.5% decline in fish weight after three months of frozen storage (Moeini, 2009).

Kilka fish, which have valuable protein and digestible fats, rich vitamins, and minerals, have attained an important position in the food-product market. Overall, the value of food products, such as kilka, depends on their nutritional specifications and acceptability in society; therefore, accurate processing and the preparation of appealing product varieties are crucial for the market (Khanipor et al., 2017).

The final step of the food-production chain is packaging, which occupies the middle ground of production, distribution, and consumption. Many small and large companies all over the world are very active in packaging industry. Competition among packaging manufacturers has led to improved quality and more types of packaging. Currently, numerous packaging and preservation methods, including nonbiological decomposable synthetic chemicals, are used for food preservation. Recently, new packaging materials—such as edible films that are biologically decomposable—have entered the market (Aguilar-Rivera et al., 2023; Kandasamy et al., 2018).

Consumer demand is high for high-quality seafood products, especially those that can retain their superior quality of taste, texture, and general fresh appearance following a prolonged period of cold or frozen storage (Bayram et al., 2021). The use of edible films for packaging kilka seems to be an ideal method for proper preservation during periods of long storage.

Edible coatings are completely water soluble and glossy; they perform just like a secondary skin and have favorable properties such as rapid attachment to foodstuff, label attachment, antibacterial, and antioxidant properties (Seifzadeh, 2022). These types of coatings protect the aroma, taste, and food color as well as help to maintain the nutritional components. Coating food products with these films can lead to preservation of food moisture and the lowering of oxygen absorption, which can substantially improve the appearance of food products. These coatings are invisible to the naked eye (LondoĂąo-Hernandez et al., 2018; Yu et al., 2019).

Whey protein is derived from milk and is composed of protein, lactose, and inorganic salts. It is anti-bacterial, antiproteolysis, and preserves food moisture (Setiadi and Sauria, 2020). Edible films made of whey protein have been used for packaging salmon, hotdogs, sausages, crackers, and frozen fish filets, and have improved their quality and shelf life (Seifzadeh, 2014). The objective of this study is to investigate the effects of a whey protein coating on the chemical, bacterial, and sensory properties, proximate analysis, and shelf life of frozen kilka.

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-π 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).

The Cool Roof Rating Council (CRRC) was established in 1998 to develop fair, accurate, and credible methods for evaluating and labeling the surface radiative properties of roofing products, specifically solar reflectance and thermal emittance. In addition, a standard practice for calculating a solar reflectance index (SRI) has been developed for horizontal and sloped surfaces. In recent years, these ratings have also been used to develop “cool walls” and “cool pavements.”

One important part of the CRRC Product Rating Program is the real-time three-year weathering process that informs product field performance over time, augmented by the Rapid Ratings Program based on ASTM laboratory aging testing. ASTM methods are also used to define the properties of the paints needed for this application.

First, some important definitions: ¹

• Solar Absorption (SA): The fraction of sunlight absorbed by a surface.
• Thermal Emittance (TE): The efficiency with which a surface emits thermal radiation. Bare metal has low thermal emittance, while nonmetallic surfaces are high.
• Solar Reflectance (SR): The fraction of sunlight reflected from a surface. High SR is the most important property of a cool surface.
• Thermal Resistance (TR): The measure of a material or system ability to prevent heat from flowing through the substrate.
• Solar Reflectance Index (SRI): A calculated value based on SR and TE that determines a material’s surface value under the conditions outlined in E1980. The higher the value, the cooler the surface in the sun (Figure 1).

FIGURE 1 Schematic for High and Low SRI Values.²

Coating Standards

There are two basic types of cool-roof coatings: elastomeric and cementitious. The properties of elastomeric coatings are governed primarily by D6083/D6083M-24 Standard Specification for Liquid-Applied Acrylic Coating Used in Roofing. This specification defines the viscosity, volume, and weight solids required for cool coatings. It also establishes the minimum efficacy standards derived from successful in-service performance throughout the United States. These performance evaluations were conducted on more than 20 roofs ranging in age from a few months to 20 years old.⁴ There are no correlating standards for cementitious cool coatings. Table 1 lists standards for evaluating other physical properties required for acrylic elastomer cool coatings.

Cool Roof Material Standards

The primary standard for evaluating SRI is E1980, Standard Test Method for Measuring Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces. The combined effects of solar reflectance and thermal emittance are measured, depicting surface temperature and energy performance. Table 2 lists standards for measuring the main variables associated with SRI along with a standard methodology for laboratory simulation of the effects of aging exposure on reflectance and emittance properties.

The use of ASTM standards governing cool surfaces provides a systematic universal basis for evaluating a wide variety of substrates that correlate well with actual field exposure for paints that ultimately save energy and cool urban heat islands.

References

1. A Practical Guide to Cool Roofs and Cool Pavements. Cool Roof Toolkit. January 2012.
2. What is SRI or Solar Reflectance Index? (accessed August 12, 2024)
3. Muscio, A. The Solar Reflectance Index as a Tool to Forecast the Heat Released to the Urban Environment: Potentiality and Assessment Issues. Climate, 2018, (6)1, 12.
4. Seyfried, E. RCMA in Review: ASTM D-6083 Made Easy. RSI Magazine. March 2000.

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 ¹1°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 ¹ 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.

Heat is the leading weather-related cause of human mortality, surpassing hurricanes, tornadoes, lightning, and blizzards. The impacts of heat are intensified by the urban heat island (UHI) effect, which occurs when cities are hotter than surrounding rural and suburban areas. Architectural coatings can play an important role in UHI mitigation by reflecting solar radiation rather than absorbing it. By efficiently reflecting sunlight and emitting absorbed heat, cool exterior walls maintain a lower surface temperature, improve occupant comfort and safety, and reduce the demand for air conditioning, which decreases the building’s contribution to peak demand, greenhouse gas emissions, and the UHI effect. This article describes methods for evaluating the “coolness” of architectural coatings, including laboratory testing and natural weathering to determine the durability of the radiative properties. It also summarizes current technologies for increasing coating solar reflectance; discusses the latest research on the impacts of cool exterior walls; describes U.S. building codes, standards, and voluntary programs that require or promote their use; and explores strategies for discussing cool coatings with customers.

Introduction

The urban heat island (UHI) effect is a growing concern among communities in the United States and across the globe. Architectural coatings that highly reflect solar radiation and emit absorbed heat are an effective tool to combat urban heat and make communities safer and more comfortable. This article outlines the issue of urban heat and offers “cool” coatings as one solution that is gaining traction. We explore how cool exterior walls work; how the cooling properties of products are evaluated; examples of current technologies; adoption in codes, standards, and programs; and how they fit into sustainability efforts and marketing in the architectural coatings industry.

The Urban Heat Island Effect

Heat is the greatest weather-related cause of human mortality—surpassing hurricanes, tornadoes, lightning, and blizzards.¹ĚýExtreme heat can also cause heat illness and increased respiratory and cardiovascular problems, which can strain health services, as well as create disruptions to key infrastructure such as power grids and water supplies.²ĚýThe negative impacts of extreme heat are intensified by the urban heat island (UHI) effect, a phenomenon in which cities are hotter than surrounding rural and suburban areas. According to the U.S. Environmental Protection Agency (EPA), daytime temperatures in urban areas are about 0.6 °C to 3.9 °C (1 °F to 7 °F) higher than temperatures in outlying areas, with nighttime temperatures about 1.1 °C to 2.8 °C (2 °F to 5 °F) higher.³ĚýThis temperature difference occurs because heat from the sun is retained in areas with a high concentration of buildings, parking lots and roads, and a lack of trees and green space (seeĚýFigure 1). Tall buildings that block or slow air movement, along with waste heat released by vehicles and air-conditioning units, contribute to the formation of UHIs. Smaller, more intense heat islands also exist within cities, and they can disproportionately affect low-income neighborhoods and communities of color.^4,5,6

FIGURE 1 Explanation of the urban heat island effect. Image Credit: Cool Roof Rating Council

Although air-conditioning can help keep buildings safe and comfortable, increased air-conditioning use also releases waste heat into the environment, exacerbating already hot temperatures. Furthermore, not all homes and businesses are equipped with air conditioning. For example, theĚýNew York TimesĚýreported that, in the heat waves that occurred in Oregon and Washington state in June 2021, an estimated 600 more people died than would normally be expected during that time period.⁷ĚýFewer than two-thirds of homes in Oregon have air conditioning, and only 44% of households in the Seattle metropolitan area have it.⁸ĚýIn Multnomah County, OR, where Portland is located, none of the people who passed away during the 2021 heat waves had central air-conditioning.⁷

In addition to the immediate threats of extreme heat, hot temperatures also have indirect consequences, such as increased formation of ground-level ozone, a key ingredient in smog and a dangerous pollutant, especially for individuals with existing respiratory conditions.⁹ĚýThe increased energy used to power air conditioners during hot times can also lead to greater use of as-needed power plants, commonly known as “peaker” plants, which are large emitters of air pollution and contribute to blackouts and brownouts due to electrical grid strain.

Heat waves across the United States continue to be more frequent, longer, and more intense,¹⁰Ěýand scientists predict that cities across the globe will be approximately 4 °C (7.2 °F) hotter by 2100 due to climate change.¹¹ĚýAs such, solutions to keep buildings and communities cooler are increasingly important.

In the past several years, many in-depth articles have been written across the industry heralding a wide variety of advances suggesting that biobased materials were on the verge of achieving explosive growth.

Some of these coatings manufactured from “natural” or ecofriendly sources are commercial and manufacturing success stories. Yet, many other developments and advancements are still waiting for the right resin, application, or manufacturing opportunity to manifest itself.

In 2019, an in-depth look at the role that academia plays in successfully making coatings “benign by design” hinted that success in mass utilization of biobased coatings must include a several pronged industry-wide approach.¹

Following up on those observations, this article further examines today’s biobased coatings world from the perspective of sustainability, standardization and industry/government/university collaboration as a basis for progress moving forward.

The Coatings Industry Sustainability Challenge

Since the turn of the century, every industry has made efforts to some extent to build sustainability into their product portfolios with varying degrees of success. Recycling was one of the initial movements to gain traction.

Simply put, if things could be reused or reinvented as a new use, less would end up in the burgeoning landfills—sort of like hand-me-downs of previous generations, but on a much wider scale.

Over the past 20 years, sustainability has evolved into a much more complex paradigm with four main pillars encompassing human, social, economic, and environmental interactions. Together, these four pillars intertwine to personify sustainability defined by the Oxford English Dictionary as “the avoidance of the depletion of natural resources in order to maintain an ecological balance.” Merriam-Webster further describes sustainability as “a method of harvesting or using a resource so that the resource is not depleted or permanently damaged.”

The coatings industry first approached sustainability through reductions in manufacturing emissions and commercially successful product developments such as water-based technologies that lowered VOCs.

Lately, the industry has continued sustainable market-wide initiatives by developing a portfolio of biobased coatings. These products attempt to substitute raw materials derived from fossil fuels with products made from plant-based biomass raw materials such as vegetable oils or sugars.

Key components of these initiatives are rooted in the use of renewable raw materials for producing biobased solvents, resins, additives, pigments, colorants, and crosslinkers. Lately, these bio-raw materials have tapped into the Renewable Carbon Initiative. Carbon dioxide that is released from a host of industrial and commercial processes is captured and used as feedstock for producing polymeric building blocks.

chnical successes but are presented and even marketed as niche products. Even today, 100% biobased coatings command only 1-3% of the global market volume. Market share rises to a generously estimated 10% if formulations that contain any amount of biobased raw ingredients are included, no matter how minuscule.

In order for biobased coatings to leap into a more mainstream view and command a larger market share, a number of hurdles still need to be overcome. The availability and price of biomaterials, as well as high technical requirements have had a limiting effect despite regulatory efforts to force the issue.

The fact is that the market for these coatings is still rather small, and production is more complex and more expensive than conventional products. Availability of renewable biomass materials would seem to be an easy challenge to overcome, but the fact remains that even renewable harvests take time to “grow” and can be thwarted by something as mutable as bad weather.

The industry is working on solutions that would be derived from biowaste, recycled content, and cellulose from carbon capture. But these solutions will take time to become practical realities.

The biobased coating market is still in its infancy primarily because the industry (which consists of individual companies trying to maximize market share and profitability) either cannot or is unwilling to invest heavily in biomass development for raw materials and in new manufacturing processes for those materials.

Research staffs across the industry have been slashed to the bare bones over the years. This leaves little time for the innovative, time-consuming, thoughtful development needed to ensure that biobased coatings and raw materials will ultimately achieve the same level of field performance and across-the-board acceptance as traditional products.

In short, the main challenges to large-scale acceptance of bio-coatings are consistent raw-material availability, affordable cost of manufacturing, comparable (or better) performance characteristics, and the time for scientists to innovate in this new dimension.

However, there are forces challenging the status quo within the coatings industry from other directions that have sparked a push to find new ways to address these dilemmas. Consumer awareness around “green” technologies is increasing, and customers are seemingly willing to reward companies that address those concerns by favoring their products.

Health problems emanating from well-publicized scandals such as excess formaldehyde in imported manufactured flooring and improperly constituted drywall that caused unexpected and enormous VOCs in the residential building industry further exacerbated the public’s growing demand for cleaner products.

Regulations are becoming more stringent around the entire paradigm of sustainability, driven in part by consumer demand and government initiatives. However, not all these challenges have resulted in punitive demoralizing actions or results.

Rather, paint companies have begun to approach the challenge differently by taking important smaller steps to develop crucial new molecules that act as “drop-ins” for segments of the paint recipe. This is especially important for balancing performance criteria and pricing competition with well-established petrochemicals.

Using drop-in building blocks provides a faster way to integrate biomass feedstock without the need to make large investments or drastically change high-capital investment production processes.

In addition, many of these monomers require UV light, oxygen, and renewable raw materials, providing more sustainable manufacturing and broader flexibility into a wide variety of markets. Examples of some of the more prominent biobased building blocks for resin synthesis are listed in Table 1.

Polyesters are formed from the reaction product of polyols and a di- or multifunctional acid or carboxylic acid and anhydride for ester linkages in the polymer chain.

Solventborne alkyds have been used in coatings for decades. However, stricter pollution regulations have nudged the development of waterborne alkyds or polyurethane dispersions (PUDs).

PUDs offer improved performance over alkyds due to the robust urethane linkages. They are linear or lightly branched and of relatively high molecular weights dispersed in water. Lower film-forming temperatures at higher glass transition temperatures can be achieved because urethanes bond strongly to water.

Latex particles swell, causing a plasticizing effect. This allows PUDs to have lower VOCs and lower film-formation temperatures together with improved mechanical, chemical-, and corrosion-
resistance properties than waterborne alkyds or conventional latexes.

Some of the more recent biobased resin technologies are low-odor, low or no VOCs, and free from phenolethoxylates (APE). Performance characteristics seem to approach solventborne counterparts, although long-term durability testing is still ongoing. In any event, this is a positive step in manufacturing biobased coatings that does not compromise performance standards.

Continue reading in the May-June 2022 digital issue of CoatingsTech.

Biobased coatings account for a small share of the paint and coatings market—approximately 5% in 2018 according to estimates of leading industry consultants.¹ That level is seen as just a starting point, though, as many in the industry predict that biobased coatings will make significant inroads in the not-too-distant future.

As consumers become more aware of and concerned about the safety and environmental impacts of the products they use—not only when they use them but also during the production and across the products’ entire life cycles—ingredient suppliers and coating formulators are driven to invest more in innovation related to biobased materials.

Several hurdles must be overcome, ranging from access to large volumes of biobased raw materials with consistent high quality to the development of biobased products that provide the same or better performance as traditional paints and coatings and at equal or lesser cost.

Even so, these challenges are considered surmountable, and expectations are high across the value chain.

A LOOK AT CURRENT OPTIONS

The use of biobased ingredients in coatings must be taken in the context of overall sustainability. Growing corporate sustainability initiatives are driving the conversation of not only biobased ingredients, but also materials that are produced using less energy, are lighter for shipping, incorporate recycled or upcycled materials, reduce petroleum-based materials, and offer lower VOC emissions, among other considerations, according to Joanne Hardy, global director of research and development at Axalta Coating Systems.

“Biobased coatings are one of many ways manufacturers can deliver sustainability benefits within the paint sector,” agrees Mary Ellen Shivetts, PPG director of global product sustainability. She notes that many raw material suppliers are introducing biobased options to the paint and coatings industry, either as part of a biobased mass balance approach or as materials certified to a specific biobased content.

Renewable raw materials are used to produce biobased solvents, resins, additives, and pigments, which are all components of coatings.

Natural oils have been on the market for some time and have been used to manufacture solvent-based products. They are now being used by companies such as allnex to produce high-solids alkyds and high bio-content, water-based alkyd emulsions/dispersions, according to Florian Lunzer, the head of corporate innovation at allnex.

These resins, he notes, find appeal in decorative/architectural coating applications. Renewable polyurethane dispersions (PUDs) based on vegetable oils (e.g., soybean, castor, and linseed) are also available and used for wood finishes, including industrial and flooring markets, adds Terri Carson, director of technical service and quality control for Alberdingk Boley. “These oil-modified products enhance the appearance of wood with excellent wood warming properties and chemical resistance from oxidative crosslinking,” she says.

DSM has commercialized a wide range of biobased resins for industrial, joinery, flooring, packaging, and decorative coatings in selected markets. “We have experienced a sharp increase in the demand across all markets, mainly for decorative and industrial coatings,” says Tim Gratzke, Decovery® marketing manager with DSM Resins & Functional Materials.

More recently, other biobased raw materials have become available on a commercial scale, including polylactic acid (PLA), which is used to replace plastics in flexible packaging applications; 2,5-furandicarboxylic acid (FDCA), which is currently used in making polymers that replace polyethylene terephthalate; succinic acid; and isosorbide; among others. Most have not yet found appreciable inroads into coating resins yet, but the potential certainly exists, according to Lunzer. Biosuccinic acid, Carson notes, is being used to produce polyols for PUDs and water-based uralkyds.

PPG has two biobased coating offerings: Johnstone’s™ Air Pure, a biobased wall paint that contains 45% biobased raw materials and enhances the indoor-air quality of homes, offices, and schools by removing up to 70% of harmful formaldehyde from indoor air, and SEIGNEURIE™ Phylopur, an interior wall paint containing a 97% biobased resin produced from plants and industrial byproducts, which is available in undercoat, matte, and velvet finishes and performs like traditional paint.

The renewable raw materials are cultivated according to a sustainable management method, reducing the use of fossil fuels, and contribute to the paint’s very low VOC emissions, according to Shivetts.

CONSUMER-DRIVEN INTEREST

Many companies have established sustainability initiatives that include being responsible and respectful to the environment by using biodegradable raw materials derived from renewable and sustainable resources.

“Developing and manufacturing products with this in mind can also help their customers meet their sustainability goals,” says Al Libal, business development manager at Werner G. Smith. “Biobased projects are therefore borne out of true partnerships that create win-win solutions.”

There are many aspects influencing the move to biobased coatings, including regulations, customer needs, and the industry’s continued focus on sustainability, according to Shivetts. “Coatings manufacturers must be willing to invest in innovation and exploration of renewable resources in order to proactively develop high-performing biobased products,” she says.

In the short-term, products that are consumer oriented will be those where biobased technologies are adopted more readily, says Steve Block, vice president of business development for NXTLEVVEL Biochem. “Regulations are driving this change, especially those related to safer chemicals for people the environment,” he says. “But there is also a market pull for biobased technologies, particularly in the decorative coatings market. Consumers are becoming more interested in natural-based products as concern for the health of the planet and impact to people increases.

“This is especially true in some areas in the United States, like California and New York, many countries in Europe (especially in Germany, U.K., and Scandinavia), and Australia,” Block says. He does note, however, that there is substantially less appetite for biobased technologies in Brazil, India, China, and Southeast Asia.

DSM’s experience has been similar, as strong demand comes mainly from the European market and is driven by end-consumer demand, major brands, big-box retailers, and legislation, according to Sandeep Bhatt, business director NMA, DSM Resins and Functional Materials.

Robert Skarvan, global marketing director for the allnex Liquid Resins and Additives Business Unit, adds that the industrial wood market in Europe is heavily influenced by Ikea, a brand owner that is well known for its sustainability practices and has a history of using biobased materials. He has seen less interest in decorative coatings to date, but views this segment and packaging applications, notably for cosmetics, as offering emerging opportunities.

There is also a growing focus on biobased coatings within the automotive sector as more consumers request biobased materials, according to Hardy. “Axalta actively tracks the megatrends in the industry, and we see sustainability as one of the most important trends today,” he says. “We are continually identifying and evaluating biobased raw materials across all regions to meet customer expectations and expand our sustainable coating offerings.”

Regulations are an important driver, too, according to John Bennett, CEO of Eco Safety Products. “Regulations to reduce carbon-emission output requires reduction of petrochemicals,” he explains. “Biobased materials that can be converted to replace petrochemicals will therefore have the most applications for broad use.”

Other regulatory pressures stem from efforts to reduce hazards to the environment. One of the key concerns—and opportunities for improvement, according to Block—is addressing the aquatic toxicity of raw materials. “Care for the environment is a universal pillar and using raw materials that have a favorable health, safety, and environmental profile are advantageous,” he observes.

GOVERNMENTAL INITIATIVES AND EFFECTS

Two government-backed initiatives directly impact the use of biobased coatings. In the United States, the U.S. Department of Agriculture (USDA) BioPreferred Program, which began in 2002, was created to increase the purchase and use of biobased products, including paints and coatings.

The two core pillars of the program are mandatory purchasing requirements for federal agencies and their contractors, and a voluntary labeling initiative for biobased products. The USDA Certified Biobased label, displayed on a product certified by USDA, is designed to provide useful information to consumers about the biobased content of the product, Shivetts says.

“This program has not only impacted the development of biobased technologies, but also the U.S. economy by millions of jobs and new market opportunities for products based on renewable resources,” Carson explains. According to USDA, Shivetts adds, the increased development, purchase, and use of biobased products reduces U.S. reliance on petroleum, increases the use of renewable agricultural resources, and contributes to reducing adverse environmental and health effects.

A newer initiative in Europe—the EU Green Deal—is anticipated to put the European manufacturing base on an accelerated green track, according to Michela Fusco, global marketing director of allnex’s Radcure Business Unit.

Bhatt, of DSM, agrees. “New environmental criteria for public tenders across Europe and the European Green Deal have led to an increased interest and adoption of biobased ingredients in coatings,” he says.

COST AND PERFORMANCE REQUIREMENTS A BIG HURDLE

As the interest in biobased materials continues to increase, the need for a clear, quantitative value proposition for each material being considered is paramount. “The challenge of creating coating solutions using biobased materials is the ability to develop a biobased product that performs equal to—or better than—existing products on the market today at equal cost,” Hardy says.

As with any new technology in any industry, Block notes, the costs in the early stages of commercialization are not at a scale where additional costs are avoidable. Consistent raw material availability at an affordable cost is also a challenge, according to Shivetts. “The switch to plant-based materials must not result in any compromise in functionality of the paint, which can present a challenge for paint manufacturers to maintain standards,” she says.

At this early stage of market development, technologies seem to be limited with the quality of the product as it relates to performance benefits under constant evaluation, Libal adds. While the raw material supply chain issues should be overcome once demand rises, achieving higher levels of adoption or conversion to biobased materials in the mainstream may be a tougher hurdle to surmount, according to Bennett.

MORE CHALLENGES

Beyond cost and performance issues, several other factors complicate the development and adoption of biobased paint and coating products. One of the fundamental challenges, according to Gratzke, is the complexity of sustainability.

“Before becoming successful with biobased ingredients one needs to understand sustainability from a holistic perspective. This was certainly one of the challenges and great learning experiences our organization went through,” he explains. “Being able to define what sustainability really means was a great challenge. It is everything from biobased content to reduced carbon footprint, low toxicity and sustainably sourced materials. These are some but certainly not all factors. Understanding the connection between these elements and building a compelling portfolio around them with our Decovery® biobased brand was a major step.”

Gratzke also notes that while the entire bioeconomy still faces plenty of challenges such as the availability of renewable raw materials at scale, great progress has been made in securing supply and expanding the toolbox of biobased monomers.

Inconsistency in the methods used for determining the content of biobased materials in a coating and the definitions for biobased coatings across industries or regions adds further complexity and confusion, according to Kevin O’Connor, global director of product management for transportation coatings at Axalta Coating Systems.

“When is a biobased coating considered biobased?” he asks. “And how much biobased material content is needed to be classified as biobased? We are working with our customers to understand their definitions and expectations around the amount of biobased content in a coating solution that would help them meet their own sustainability objectives.”

Another hurdle for biobased ingredients is ease of incorporation. “It is much easier to incorporate a biobased solvent with the same chemical structure as the conventional solvent,” O’Connor explains. “Conversely, incorporating a biobased monomer into a new polymer system that is ultimately incorporated into the coating formulation is far more challenging. The biobased solvent may not impact the final performance of the coating, while the new monomer is far more likely to impact final performance.”

Lunzer agrees, noting that true biobased molecules that can be used as one-for-one replacements of existing petrochemicals do not happen often. “In most cases, changing the raw material base to a high biobased content requires the development of a completely new product in order to adapt the overall composition to the properties of the new raw materials,” he says. “Like-for-like substitution is often only possible if the downstream users are willing to accept the mass balance approach to calculating bio content.”

The slow rate of adoption of new materials by the coatings industry is another issue. According to Block, it discourages the development of new biobased technologies and creates exceptionally long periods for recovery of investment costs.

Gratzke concurs, noting, “The sustainability trend is a great opportunity, but it is extremely difficult to achieve with speed.”

He stresses that because it is such a challenge to formulate biobased resins and coatings that perform well, are affordable, and truly sustainable, collaboration across the value chain will play a vital role in the transformation of the market.

“We’ve made very positive experiences in connecting all the stakeholders across the value chain to make this happen and would like to emphasize that we are very open to any form of collaboration to satisfy the demand for biobased resins and coatings,” Gratzke says.

It is also important to remember that there are downsides to putting too much emphasis on any on any singular sustainability concept or goal. “A balanced approach is needed,” says Fusco. “And perhaps the main reason we don’t have strong biobased legislation today is because a balanced approach has not yet been found. It’s not an easy issue.”

The approach allnex has taken with its sustainable portfolio management when building the ECOWISETM portfolio is to assess the product sustainability performance across five different eco pillars that include renewable sourcing as well as the use of safer materials, VOC emissions, circularity, and energy efficiency, Fusco notes. “This approach ensures we make balanced choices based on multiple aspects of product impact on people and the environment,” she explains.

CONSIDERATIONS FOR BIOBASED INGREDIENT SELECTION

When it comes to reducing the carbon footprint of its products, AkzoNobel uses both biobased materials and materials containing recycled content. When choosing sustainable ingredients, the company’s approach takes into consideration some of the challenges that come with the use of biobased ingredients, according to Job Coenen, business development manager for sustainability with AkzoNobel.

“Customer research confirms that while there is openness to consider biobased, lower-carbon-footprint solutions, only few customers are prepared to pay more or sacrifice on quality for them,” he says. “The costs of making biobased raw materials are often still higher than conventional raw materials and can still be a challenge to match product performance. We also don’t want our biobased ingredients to compete with the food chain. And finally, we see that not all suppliers of biobased materials can supply the full LCA [Life-cycle Analysis] data needed to support any product claims.”

Axalta also considers several factors for biobased ingredients before incorporating them into a coating formulation, including
ease of incorporation into an existing formulation; total cost to incorporate the candidate material versus a conventional material; performance of the candidate material versus a conventional material; how the use of the candidate materials impacts other important value chains; and whether there is quantifiable evidence that the candidate material reduces the scope 1, 2, or 3 greenhouse gas (GHG) footprint compared with the conventional material.

STANDARDIZATION/CERTIFICATION & MARKET ADOPTION

The lack of consistency in defining biobased materials should be addressed with some form of standardization. “Standardization can play a very important role in advancing biobased coating technologies” Bhatt says. “It should be the goal to establish measurable and objective criteria to benchmark one solution to another.”

Certifications and product labels, Carson adds, are a source of information for defining technical specifications and compliance to a specific standard. They also help to promote awareness of biobased technology that is needed, in part to increase the usage/demand of these products in more market areas.

Any type of standard is intended to create consistency and industry acceptance, Block says. Standards are important, he says, so both coating manufacturers and raw material suppliers have uniformity. “However, as technologies develop, industries should look to ensure any standards are reflective of current technologies while still enabling the introduction of new technologies without creating unintended barriers,” he says.

Standardization and certification would also play a role in how a biobased coating technology is marketed and the influence the consumer would have to demand more biobased materials, according to O’Connor.

“Today, there is no certified ‘biobased coating’ composition threshold that allows coatings to be officially labeled as a biobased coating,” O’Connor explains. “We believe standardization and certification of such a threshold would be welcomed in the coatings industry and could accelerate the adoption of biobased coating technologies. Developing biobased coating technologies is an intricate process and one that we at Axalta believe requires standardization to gain momentum.”

For its Decovery® solutions, DSM has elected to use biobased feedstock that can be verified with the C14 standard even at the end-user level, according to Bhatt. “This measurement methods allows quite accurately the determination of the biobased content in a material and hence creates a high level of transparency and trust,” he explains.

Batt says that this standard is gaining acceptance in several European countries now, but there are many more elements that can and should be standardized beyond biobased content, such as the environmental footprint.

Bennett would like to see oversight and standardization regarding the impacts of biobased material development on the balance of the entire ecosystem all the way to responsible farming. He says he is concerned, however, that dictating how much biobased content should be in a product could result in products not meeting the best performance objectives.

“Formulating safely and sustainably also involves product lifespan and performance,” he says. “Certified testing of how much biobased content would serve the ultimate goal just as well and most likely better.”

Hardy believes that coating and raw material suppliers should consider Life-cycle Analysis (LCA) standards, including ISO 14044 and ISO 14067, for quantification of the GHG footprint of raw material and coating technologies.

One example of an industry-led initiative worth noting, according to Shivetts, is the U.S. Green Building Council (USGBC) Leadership in Energy and Environmental Design (LEED) green building ratings, which are considered a standard for green building initiatives for companies that wish to earn LEED certification for their projects. “While biobased coatings are a smaller portion of the overall industry, it is anticipated that they will become more prominent in years to come as customers continue to seek sustainable solutions,” she says.

ANTICIPATING THE NEXT WAVE OF COMMERCIALIZATION

Part of the excitement around biobased paints and coatings is the high level of innovation activity in the space. “While there are a relatively small number of biobased paints and coatings within the current marketplace, further research and development will allow greater understanding of biobased materials and their performance,” Shivetts says.

She adds that all segments within the paints and coatings industry are open to the possibility of biobased coatings alternatives, but in some segments, additional research and development work is needed to ensure product performance.

Leading suppliers and developing companies are investing heavily in surfactant, solvent, and coalescing agent technologies, among others, because the coatings industry provides significant business opportunities, according to Block.

“There is an increasing number of companies who are developing biobased technologies for the coatings industry, many of which are young, dynamic firms where the rate of change is accelerating and could contribute step-change innovations,” he says. “I would anticipate a broad set of technologies to meet the ever-changing market needs, with many of those products coming from developing companies that can rapidly deliver impactful technologies.”

Block points to technologies using both enzymatic and catalytic methods and those leveraging carbon dioxide as a feedstock as key biobased approaches gaining the attention of the coatings industry.

Acrylic acid and acrylate monomers represent some of the most important biobased monomer groups to watch out for in the future, according to allnex’s Skarvan.

In general, biobased ingredients that are easily incorporated into existing formulations and that have clear, quantifiable benefits, in terms of reduction of total GHG footprint, are anticipated to be commercialized in the near term, according to O’Connor.

DSM is focused on rapidly growing its biobased portfolio in the markets it currently services, according to Gratzke, but he notes that the company is screening for potential markets to enter with its Decovery® biobased technology. Gratzke says he believes the entrance of other players into the market is a good development. “The dynamic nature of the sector reflects the growing demand for biobased coatings and brings us closer to our goal of accelerating the transformation of the coatings market towards renewable ingredients,” he says.

Meanwhile, Alberdingk Boley will continue to pioneer the development of biobased PUDs, with a focus on the development of novel castor and linseed oil-based dispersions and polyols. “We offer renewable alternatives for many of our standard PUD grades, and we’ll always commit our efforts to deliver valued biobased solutions,” Carson says.

Eco Safety Products, meanwhile, is nearing completion of the development of biobased antibacterial and antiviral additives, according to Bennett. The company is also working on biobased hybrid epoxy urethane binder systems for the formulation of numerous decorative aggregates. These products use biobased content from nuts, soy, chitin, starch, and cellulose and will be formulated into decorativeĚýfloor and countertop coatings.

Carson cites IVC Chemicals as another example. The company recently partnered with Green Delta to produce biorenewable UV products as part of the Life BioPaint project. “These products,” she says, “were manufactured in a fully automated, closed-circuit process developed with zero-VOC emissions, minimal waste, and with lower energy useĚýduring production.” A full range of 100% UV-cure coatings has been developed with renewable content up to 70% for furniture, doors, panels, and flooring.

AkzoNobel has also been active in the biobased coatings space. The company recently announced a biobased innovation developed in collaboration with the Dutch Advanced Research Center Chemical Building Blocks Consortium (ARC CBBC). “This completely new, breakthrough curing technology uses biobased monomers and requires just UV light, oxygen, and renewable raw materials, offering a more sustainable way of making resins,” says Coenen.

He also notes that AkzoNobel often seeks solutions for overcoming the hurdles to biobased coating development and commercialization by partnering with others. The company’s collaborative “Paint the Future” innovation ecosystem includes suppliers and other industry “newcomers,” such as startups and academia, with the goal of bringing innovations to market by pushing the boundaries of the paints and coatings industry.

Courtesy of AkzoNobel

“The goal is to be able to offer our customers cutting-edge, sustainable solutions, and the new biobased curing technology is a fantastic example of collaborative innovation in action,” Coenen explains. “This new product is just one demonstration of how AkzoNobel is opening up a new future for paints and coatings by using sustainable building blocks that will enable us to explore and develop some really exciting functionalities for our customers.”

AN EVER-GREATER DIFFERENTIATOR

As the world faces countless challenges related to climate change, the international community has recognized that it is time to act. As a result, Bhatt says, sustainable and biobased ingredients will disrupt the coatings market.

“Our market insights show a continuously increasing demand for sustainability attributes in coatings products,” he says. “Performance and price are still of very high importance, but sustainability is at the moment a great differentiator and will most likely become a qualifying criterion in the long run.”

Block says he sees four pillars as necessary for success: performance, scale, affordability, and environmental impact. Each of these factors, he says, also has a role to play in the adoption of new biobased technologies.

Block also agrees with Bhatt, noting that the importance of environment impact has been growing with many suppliers and coatings manufactures, as reflected by the greater numbers of companies developing corporate Environmental, Social, and Governance (ESG) goals.

“These initiatives are supported by company stakeholders and investors as concerns such as climate change, personal health, and protecting our natural environment are rapidly rising in board rooms across the supply chain,” he says.

Libal also believes biobased technology is becoming increasingly significant in the marketplace despite the numerous obstacles they face.

“The importance of biobased solvents, resins, additives, and pigments will only increase as the world moves toward the measures of reducing carbon footprints and dependence on non-renewable resources,” he concludes.

While there is still a long way to go to explore the scope of biobased technologies, Coenen says these and other sustainable solutions will almost certainly define the future of AkzoNobel products.

Coenen explains that with its “People. Planet. Paint.” approach to sustainability, AkzoNobel is embedding sustainability into everything it does and reducing the impact on the planet by offering its customers innovative and sustainable solutions—that, for example, have a lower carbon footprint.

“In both the paints and coatings market segments, we are exploring the use of biobased ingredients as an alternative to the fossil-based economy,” he says. “With our size, scope, and volumes as a large, global company, biobased ingredients will make a substantial contribution to our sustainability ambitions. By 2040 or 2050, there is a good chance we might only be using biobased monomers in our resin production, which will help us to reduce the overall carbon footprint of our products.”

At Axalta, sustainability is considered one of the most important megatrends across many industries. “As customer and consumer interest in sustainability continues to increase,” Hardy says, “the development of new biobased products will also continue.”

References
1.   Gesthuizen, Jan. Bio-based coatings overview: Increasing activities, European Coatings, Aug 27, 2020. https://www.european-coatings.com/articles/archiv/bio_based-coatings-overview-increasing-activities (accessed Apr 7, 2021).

May 2021 | Vol. 18, no. 5

Kyle Kim and Christian Lenges, DuPont Nutrition & Biosciences

INTRODUCTION

Advances in the performance of formulated products through material innovation continue to drive innovation and growth. At the same time, it is becoming increasingly paramount that new materials are also sourced from ideally renewable and overall more sustainable feedstocks using benign processes to meet criteria required within a circular economy context.

Progress in architectural and industrial coatings has focused on providing not only improved paint performance but also optimizing aspects such as pigment efficiency (e.g., reduction of TiO₂) and effective gloss management, while maintaining key characteristics such as abrasion performance and overall coating properties. At the same time, continued emphasis has been placed on reducing the environmental footprint through lower volatile organic content (VOC) in paint systems. In addition, increasing efforts have been directed to eventually replace typical petroleum-derived building blocks in coatings formulations with more sustainable, potentially renewable material alternatives.

However, the transition to performance-advantaged renewable building blocks, which are accessible at an enabling cost position and are also based on fungible, readily available raw materials produced in a sustainable and scalable industrial process, remains challenging across material industries. This article discusses one specific example of renewable based additive technology to meet the stated industry performance needs and objectives.

Engineered Polysaccharide Fundamental Material Properties

Structurally, polysaccharides are highly diverse biopolymers composed of repeating glucose units linked via glycoside bonds. The range of polysaccharide structural characteristics, such as linkage isomers, the degree of polymerization, chain branching, and aggregation through strong intermolecular hydrogen bonding, allows these materials to be found in nature as structure-forming, essentially insoluble, highly aggregated materials (e.g., cellulose) or as water-soluble thickening materials with often various biological functions (e.g., starches, various gums).

The interaction of individual polysaccharide polymer chains through hydrogen bonding to form associated supramolecular structures allows for deliberate material engineering from the nano to micron scale. For example, extensive works on various process options to access and control submicron-scale cellulose-based materials (i.e., micro-/nano-fibrillated cellulose, micro-/nano-cellulose) are reported.^1,2 Enzymatic polymerization allows for a novel, controlled path towards engineering of nano- to micron-scale primary structures within aggregated, typically micron-sized polysaccharide materials. Efficient and scalable methods to apply a monomer-based (e.g., sucrose), controlled polymerization protocol using an enzyme catalyst to engineer polysaccharide materials is emerging for first commercial, large-scale applications.

The specific family of biocatalysts is selected from the general class of glucosyltransferase (GTF) enzymes, and the polymers can be produced by reacting a solution of sucrose with this GTF enzyme. For the work described here, the alpha-1,3-glucan utilized has a typical degree of polymerization of 800 glucose repeat units with a polydispersity in the range of 1.7–2.0, as controlled by the polymerization process conditions (Figure 1).

The alpha-1,3-glucan polymer generated in the enzymatic polymerization process is isolated as a water-insoluble, semicrystalline, highly structured material. Significant association through hydrogen bonding generates primary particles with a narrow particle size range (~10–30 nm), which further aggregate and agglomerate to form spherical particles in the range of approximately 500–5000 nanometers (Figure 2).

The polysaccharide isolated from this biopolymerization process is a free-flowing white powder that is water insoluble but water dispersible. It is hydrophilic with an open microstructure that is colloidally stable and can be redispersed under shear to form a colloidal dispersion in water, which shows high viscosity and is shear thinning. Polysaccharides in general are hydrophilic materials and will show a significant extent of associated water at equilibrium; however, the solubility in water will depend on the linkage, the molecular weight, and the degree of intramolecular chain association through hydrogen bonding. For example, linear dextrose (alpha-1,6-glucan), a typically water-soluble starch (blend of alpha 1,4 and 1,6 glucans), usually swells and expands in water, while typically cellulose (beta-1,4 glucan) though hydrophilic, remains undissolved in water and requires strong aprotic or coordinating solvent systems to generate true solutions. The alpha-1,3-glucan utilized in this work is also water-insoluble, similar to cellulose.

Figure 3 shows the shear viscosity of a 7 wt% colloidal dispersion of alpha-1,3-glucan in water. Black dots in the figure show the typical shear-thinning behavior of the material, while the shear stress of the sample is shown with red dots. At low shear rate, the shear stress shows a plateau, indicative of the yield stress required for the sample to flow.

Figure 4 shows the viscosity of the colloidal dispersion increasing with solids loading. For concentrations > 10 wt% the system transitions from a flowing system to a soft solid.

The transition from a flowable dispersion to a soft solid at low loading levels indicates that the spherical particles generate a highly structured phase.

The alpha-1,3-glucan is of high compositional consistency and purity and does not contain significant amounts of coproducts commonly found in other polysaccharide materials used for industrial applications (e.g., lignin or hemicellulose in cellulose products or various proteins in starch products) and typically contains < 0.2 wt% monosaccharide impurities. Based on the design of the enzyme, the process provides the target polymer with essentially exclusive selectivity, producing a linear polymer with greater than 99% alpha-1,3 linkages.²

Compatibility with Paint Systems

Based on the described characteristics of the alpha-1,3-glucan material to form stable colloidal dispersions in aqueous systems, the material can also be formulated directly into various waterborne resin systems used in the coatings industry. For example, acrylic latex, vinyl acetate ethylene (VAE) latex, alkyd resins, and epoxy resins all have been used in combination with this material to generate formulated systems.

High-shear mixers typically used in the paint industry with standard settings (i.e., Cowles blade mixer) are used to effectively disperse (or grind) the agglomerates of alpha-1,3-glucan into the latex or resin systems (i.e., VAE, acrylic, epoxy, alkyd), which generates well-dispersed and stable formulations with the polysaccharide with a typical particle size range on the nano to micron scale. Upon isolation, these structures will further aggregate to larger agglomerates. However, these latex or resin dispersions are homogeneous under application conditions and do not phase-separate (data not presented in this article), thus providing systems with excellent stability in typical formulations for paints and coatings.

The addition of dispersants or surfactants (i.e., siloxane surfactants, aminomethyl propanol) during grinding may aid in achieving the desired degree of dispersion and the associated desired particle size and stability. This ease of processing with standard industry application equipment and infrastructure is important for the utility and commercial viability of new materials in coating applications. The new polysaccharide material provides advantages compared to other emerging new materials (i.e., cellulose-based particle technologies) through the ease of processing into typical paint systems.

The objective of this work was to demonstrate the utility of alpha-1,3-glucan in architectural paint formulations, especially synergistic performance in combination with typical pigments.

EXPERIMENTAL

VAE Latex-based Interior Paint Formulations with Varying PVC—Model Architectural Paint Formulations

In typical latex formulations, improvements in rheology, opacity, tint strength, and whiteness are desired and are being demonstrated in new-generation formulations. Rheological properties of the paint formulations were measured using a Brookfield RVD viscometer. For optical properties (e.g., opacity, tint strength, whiteness), following ASTM D 2244-16, 3-mil wet drawdown films were prepared on standard drawdown cards (5.5 x 10 in.) and dried at ambient lab temperature for 24 h before analyzing the optical properties using an imaging spectrocolorimeter (X-Rite). After the optical analysis was completed, select drawdown films were used for cross-section scanning electron microscope (SEM) analysis (Figure 5).

Table 1 shows the representative paint formulations for a white VAE architectural paint at three pigment volume concentration (PVC) levels.

Optical Enhancement and Displacement of TiO₂

In this experimental design, the amount of TiO₂Ěýwas displaced by the indicated amount of alpha-1,3-glucan designed to keep the overall PVC of the formula constant. Commercially available extenders (i.e., 0.7 or 3 mm calcium carbonate, hollow latex particles, calcined kaolin) were included in this study for comparative analysis. Optical properties, such as tri-angle gloss, L, a, b color values, and dry opacity, were measured on the cured films. Each point in the plots in Figure 6 (and Figures 7–9) signifies a single data point representing a specific formulation. The experiments were designed to evaluate the impact of alpha-1,3-glucan addition on the optical properties as the displacement of TiO₂Ěýwas increased in the formulation. The data is considered indicative of the impact of the additives to the formulations, providing a consistent trend (as shown in the figures).

Typical additives used as TiO₂ extenders will often also maintain optical properties at low replacement levels; however, as the extent of TiO₂ displacement increases, the optical properties will quickly start to decrease. Interestingly, this is not observed as alpha-1,3-glucan is used in these formulations (Figure 6–9). As shown in Figure 6, for 55% and 65% PVC, the addition of alpha-1,3-glucan allowed for significant TiO₂ reduction (30% reduction) without compromising whiteness (L*) or opacity (Y), whereas the additives used in comparison were able to only maintain the whiteness and/or opacity up to 8% to 15% TiO₂ replacement. In fact, displacing TiO₂ with an equivalent volume of alpha-1,3-glucan material-enhanced whiteness and opacity considerably, up to 23% TiO₂ replacement for 55% PVC and up to 15% TiO₂ replacement for 65% PVC. However, for the 45% PVC formulation both alpha- 1,3-glucan and alternative extender products were not able to displace TiO₂ adequately while also maintaining opacity and whiteness. Full data tables on the analysis can be found in Tables A.1–A.9 in the Appendix.

To assess the performance of these formulations with TiO₂ displacement with regard to tinting, blue tint was added, and the optical properties of the dried drawdown films were analyzed, as shown in Figure 7. The blue tint strength data (Figure 7) shows that, for all three PVC systems, when alpha-1,3-glucan was used as a TiO₂ displacement additive, the blue tint strength was very close to the control system and able to pass the typical quality control test used in the paint industry.*

To visualize the alpha-1,3-glucan’s mechanism of efficiently displacing TiO₂, cross-section SEM images of the dried drawdown films were prepared as shown in Figure 5. The cross-sectional SEM imaging of cured films revealed that incorporation of alpha-1,3-glucan causes significant de-agglomeration and improved homogenous spacing of TiO₂ particles throughout the matrix of the film for 65% and 55% PVC. For 45% PVC, although there is qualitatively improved spacing of TiO₂ observed, the efficiency is much lower compared to the higher PVC% films. This supports the hypothesis that the glucan additive may function as an effective TiO₂ extender, especially in high PVC paint systems.

The alpha-1,3-glucan formulation additive shows reduced efficiency of extending TiO₂ at lower PVC. This may be based on the micron-scale particle size distribution of alpha-1,3-glucan as used in this format. Although the surface area of the alpha-1,3-glucan as measured was above 150 g/m², the particle size averages around 5 to 10 mm, limiting the potential of extending TiO₂ at low PVC. To further developĚý alpha-1,3-glucan as a more universal TiO₂ extender with performance at all typical ranges of PVC, the average particle size of theĚý alpha-1,3-glucan was further reduced to 0.5 mm through control of the bioprocess conditions. As the average particle size of alpha-1,3-glucan was decreased, the crystallinity index (XRD powder diffraction) was increased from 0.56 to 0.76. This increase in crystallinity suggests that the alpha-1,3-glucan chains show higher alignment, which will result in denser average particle structure at a fixed mass (decreased particle size). The engineered polysaccharide alpha-1,3-glucan can be formed in these two distinguished product forms, alpha-1,3-glucan and microcrystalline alpha-1,3-glucan (MCG) with lower particle size distribution and higher crystallinity.

The performance of MCG in displacing TiO₂ under the same formulation conditions as described for alpha-1,3-glucan and benchmark products is shown in Figure 8. In comparison, alpha-1,3-glucan and calcined kaolin data are included and are the same data extracted from Figure 6. In all three PVC conditions, MCG consistently has a higher opacity and whiteness compared to controls including the lower PVC conditions (45% PVC). This suggests that further TiO₂ reduction is viable without direct replacement through other pigments.

Similar to earlier evaluation results, the blue tint strength of MCG-containing formulations was compared to the control system as shown in Figure 9. In comparison, the alpha-1,3-glucan and calcined kaolin data from Figure 7 was included in Figure 9. Interestingly, for the examples using MCG, it was observed that for all three PVC systems the color of the blue-tinted system was “whiter,” suggesting that to obtain the target blue tint strength to match the blue tint strength of the control sample, the amount of TiO₂ in the paint system required further reduction. This is consistent with the opacity and whiteness of the white paint formulation examples shown in Figure 8. In both situations, MCG had, in fact, overextended the TiO₂.

Rheological Enhancement Properties of Glucan

Both forms of glucan additives (alpha-1,3-glucan and MCG) also demonstrated a significant ability to increase viscosity at low concentrations in the formula in a dose-dependent manner, along with attractive shear-thinning rheological characteristics (Figure 10). This rheological activity of the glucan additives is anticipated to result in an overall reduction of other rheology modifiers typically included in the formula to control application performance.

Stain Resistance Properties of Alpha-1,3-Glucan Formulated Paints

Incorporation of the alpha-1,3-glucan materials into various architectural systems has consistently demonstrated that this additive does not negatively impact stain performance and, in certain instances, can even improve stain performance. Paint films utilized in the stain-resistance evaluation were prepared by drying the paint films on solid white drawdown cards for seven days at ambient lab temperature. Different stains were applied onto the dried paint film and were left to equilibrate for 10 min, then a dry paper towel was used to wipe away the excess stains. Next, a paper towel, wetted with nonabrasive ASTM scrub media, was applied onto a new dry paper towel, and the stains were rubbed for 10 double rubs or until a difference was noticed. Typical results are shown in Figure 11.

Performance of alpha-1,3-glucan-formulated paints show matching performance when exposed to typical stain examples. In some cases, the glucan-containing paint is less impacted by the stain challenge.

CONCLUSIONS

The engineered polysaccharide alpha-1,3-glucan accessible through enzymatic polymerization has been used in architectural paint formulations to demonstrate performance synergies. The alpha-1,3-glucan was provided in two particle morphologies, which were assessed in different PVC paint formulations replacing TiO_2. Also, these additives were tested for their ability to modify the rheological and optical properties of waterborne architectural coatings. The findings presented in this article suggest that at relatively minor concentrations, the engineered polysaccharide has the capacity to function as a substantial rheological-modifying (thickening) agent with attractive sheer-thinning characteristics. In addition, it was observed that the engineered polysaccharide significantly enhances opacity, whitening, and tint-strength of a diverse range of latex systems. These optical enhancements may allow for the reduction of TiO₂Ěýwithout compromising the optical features of the paint.

The compatibility of the polysaccharide additive was demonstrated across a host of different latex resin systems and modifiers. The multifunctional nature of the glucan offers several degrees of freedom and considerable formulation-design flexibility, allowing formulators to adjust other components in the formula to balance physical performance and cost. A multifunctional material that offers rheology engineering, opacity building, whitening, and tint strength could be an attractive new additive for coatings where several important functional properties of the coating system can be directly improved using one additive technology.

References

1. Habibi, Y., Lucia, L., and Rojas, O., “Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications,” Chem. Rev., 110 (6), 3479–3500 (2010).
2. Klemm, D., Kramer, F., Moritz, S., Lindström, T., Ankerfors, M., Derek, G., and Dorris, A., “Nanocelluloses: A New Family of Nature-Based Materials,” Angew. Chem. Int. Ed., 50 (24), 5438–5466 (2011).

Appendix

Ěý

CoatingsTech | Vol. 17, No. 5 | May 2020

Many industries today recognize the need to improve the sustainability of processes and products. The paint and coatings sector is no exception. The development of “greener” products is no longer driven simply by regulatory changes, but also by the need to meet customer expectations and the desire to realize the economic, social, and environmental advantages that many sustainable solutions can offer. There is still much to be learned, however, and academic researchers in universities around the world are exploring many of the fundamental questions about the potential of greener raw materials and the resins and other ingredients derived from them to yield cost-effective, high-performing paints and coatings.

Green Evolution

The concept of “green” has evolved over time into the broader context of sustainability, according to Mark D. Soucek, professor of Polymer Engineering at the University of Akron. “The initial focus on environmental issues graduated to a focus on using greener materials and making coatings ‘benign by design,’” he says. “The last frontier will be making sustainable coatings using green starting materials and processes that yield green formulations,” he adds. While regulations on volatile organic compounds (VOCs) continue to drive industry, there is also a significant push to find safer materials for applications where both workers and end users may be exposed to hazardous chemicals. One example noted by Dean C. Webster, chair of the Department of Coatings and Polymeric Materials at North Dakota State University (NDSU) is the active search for alternatives to isocyanate curing chemistry.

Many Challenges Remain

There are challenges, of course. Any new coating technologies compete with existing commercial technologies that have been accepted by the market, according to Webster. “New coatings must be competitive with respect to performance and cost; being greener or more sustainable isn’t sufficient,” he explains. Biobased raw materials face other hurdles. “There is a lot to be done yet regarding the supply chain for raw materials derived from biomass. Few of these raw materials are manufactured at large scale today, and there can be issues with the consistency of their quality and characteristics year to year and crop to crop,” says Vijay Mannari, professor of Polymers & Coatings in the School of Engineering Technology at Eastern Michigan University.Ěý The limited availability is a real concern, according to Andriy Voronov, professor of Coatings and Polymeric Materials at NDSU, because the mechanisms that can be used to produce resins for coatings are typically limited to free radical or condensation polymerization. “Green coatings development is directly related to the development of libraries of monomers that can be produced cost-effectively at commercial scale,” he comments. With oil prices driven much lower in the wake of the shale oil and gas boom, biobased materials currently have difficulty competing on a cost basis, even with government incentive programs.

Ghasideh Pourhashem, assistant professor in the Department of Coatings and Polymeric Materials at NDSU believes that a lack of standards for green or sustainable coatings is also hindering their development. “Better regulations and policies, including the establishment of specific standards or mandatory regulations for green and biobased coatings that have to be followed would benefit everyone,” she says. In particular, she would like to see standards that address the entire supply chain and not just the environmental and health benefits of the final coating formulations. “The impact of coatings begins long before they are made with the basic raw materials that are extracted from the earth or biomass. We, therefore, need standards that account for the entire supply chain when determining the greenness or sustainability of paints and coatings,” she explains.

The conservative nature of the coatings industry is yet another challenge, according to Voronov. “While interest in more sustainable materials for use in coating formulations is definitely growing, there are only a few companies willing to take on the significant risk associated with using novel ingredients. The situation is changing, and there are numerous companies with stated plans to expand their portfolios with greener products over the next 10 years.”

Only a Matter of Time

The question, according to Sergiy Minko, Georgia power professor of Fiber and Polymer Science in the Department of Textiles, Merchandising and Interiors and the Department of Chemistry at the University of Georgia, is not if more sustainable technologies will be adopted, but how long it will take. “The future direction of the coatings sector is to be more sustainable. It will take time to address the technical, economic, and political aspects, but the time will come when sustainable materials and green chemistry are the norm,” he asserts. The role of academic researchers, Webster adds, is to perform the basic research needed to understand the chemistry and properties of various new polymers and what needs to be done to develop sustainable alternatives that meet the cost and performance requirements of industrial applications. “There is always a combination of technical push and market pull, and today we are still at the technical push stage. Scientists are looking at what materials are available from biomass and how they can be functionalized, transformed, or even directly used in coatings. We are completing the essential basic research in order to develop new materials that can then be evaluated for their benefits by actual users,” he concludes.

Manipulation of Soybean Oil

Seed/vegetable oils have long been used by the coatings industry—alkyds are a prime example. Many academic researchers are exploring a wider range of plant-based oils, novel derivatives, and the use of different comonomers with the goal of improving the performance characteristics of biobased resins in paint and coating formulations.

Webster has been developing epoxidized sucrose soyates, 100% biobased materials generated from the reaction of soybean fatty acid with sucrose followed by epoxidation using hydrogen peroxide. The epoxidized sucrose soyates possess larger numbers of epoxy groups that can be used in curing processes to generate thermosets, which have applications in the construction, automotive, appliance, and furniture industries. “We view these epoxidized sucrose esters as a platform technology that can be converted via multiple mechanisms to many different types of resins with wide ranging properties,” states Webster. For instance, they can undergo photopolymerization, thermal crosslinking with anhydrides or blocked acids, or water-assisted acid crosslinking. They can be converted to polyols that can then be used to generate polyurethanes (PUs) with unique properties. The sucrose soyates can also be derivatized into carbonates, acrylates, or methacrylates, which also have a wide range of curing options and afford resins with interesting properties.

“One major advantage we are realizing with this technology relates to the high functionality of the sucrose soyates. They provide high crosslink densities, yielding coatings that are hard and tough. One of the traditional challenges with vegetable oil-based coatings has been achieving the necessary physical and mechanical properties. We have overcome that issue with these materials,” Webster notes. He has even explored their use in composites with natural fibers. In many cases, the new coatings and composites that Webster has developed using the epoxidized sucrose soyates have properties competitive to those obtained using petrochemical-based materials. Some of this work is being done through the Center for Sustainable Material Science, a National Science Foundation-funded collaboration between researchers at NDSU and several other universities with a focus on investigating chemicals derived from biomass for the preparation of polymers and composites.

Mannari’s group at Eastern Michigan University is also investigating coatings based on resins made from soybean oil derivatives. In one example, the soybean oil is reacted with biobased itaconic acid to form a polyester that is used as a major component in UV-curable green UV-LED gel nail polishes. “Nail polishes are one of the most widely used products in the U.S. cosmetic industry,” Mannari observes. He notes that by 2020, 122 million Americans alone are expected to use them. Gel nail polishes are attractive because, once crosslinked under UV radiation, they have much greater durability than conventional nail polishes. The gel nail polishes his group has recently developed are green for several reasons: they are cured using UV-LED radiation and are either zero-VOC solventborne or water-based formulations, including polyurethane dispersions, comprising approximately 50% biorenewable content. Mannari is not satisfied, though. “We are working to increase the biobased content by incorporating other biobased materials such as derivatives of gum/wood rosin, cardanol, and sorbitol, to name a few, as components in the formulations,” he comments.

In a separate project, Mannari is exploring the development of bisphenol-A-free (BPA-free) epoxy resins predominantly from biobased resources. “There is good demand for BPA-free products due to the increasing concerns regarding the use of BPA, especially in food packaging and consumer products,” he notes.Ěý Mannari is also developing waterborne UV-curable polyurethane wood coatings based on epoxidized soybean oil polyols with varying chemical structures and hard to soft properties. These formulations also include rosin. He intends to investigate this biobased approach for the development of packaging coatings given that this market is very much interested in renewable and recyclable materials.

ĚýBiobased Latexes

One of the challenges in developing waterborne latex coatings using resins based on plant and vegetable is that these oils are very hydrophobic, and it is difficult to achieve an acceptable solids content (~40%) and high molecular weight during emulsion polymerization via a free radical mechanism, according to Voronov. For commercial applications, he notes that 99% conversion with no residual monomers is needed. To tackle this challenge, Voronov’s group has established a library of vinyl monomers prepared in one step from soybean, canola, sunflower, high-oleic soybean, hydrogenated soybean, and corn oils. The researchers have been exploring how these monomers act during free radical emulsion polymerization, both for the formation of homopolymers and copolymers (with commercially available monomers such as methyl methacrylate, styrene acrylate, etc.). High-oleic soybean oil is an attractive option because it has high heat stability, improved shelf life due to enhanced resistance to oxidation, and a better controlled composition because it is monounsaturated.

“We anticipated that there would be fundamental challenges, including insufficient conversion due to the hydrophobicity of the monomers. The first step was to investigate the kinetics, reactivity, and other fundamental characteristics to identify opportunities for optimizing the polymerization to achieve better properties and performance,” Voronov observes. One approach employed to increase the conversion was to perform the reaction as a mini-emulsion. This method is more suited for hydrophobic monomers because the initiator is not soluble in water but soluble in oil, which potentially causes the polymerization to take place in oil droplets rather than in micelles, as is the case with traditional emulsions. His group has been able to easily achieve 95–97% conversion, which is not sufficient for commercial products, but is good enough for initial proof of concept testing.

Vinyl monomers are indeed polymerizable with a broad variety of vinyl counterparts, providing a versatile platform with different properties achievable depending on the choice of oil from which the monomer was derived.

“We have been able to show that the vinyl monomers are indeed polymerizable with a broad variety of vinyl counterparts, providing a versatile platform with different properties achievable depending on the choice of oil from which the monomer was derived,” says Voronov. He notes that one of the advantages of these resins is that unsaturated fragments are present that allow for crosslinking. “We can realize a broad range of properties, which allows for optimization of the desired combination of strength, flexibility, and toughness,” Voronov asserts. So far, the solids content has been sufficient too, but while close, 99% yields have not yet been obtainable. In addition to working on that goal, Voronov is exploring comonomers from the same seed/plant oils but with different chemistry to enable the production of 100% biobased resins. He is collaborating with a French group that has synthesized a biobased monomer containing a benzene ring that when copolymerized with the oil-based vinyl monomers provides resins that impart some strength to coatings. Voronov has also investigated acrylic monomers prepared from cardinol, which is obtained from cashew nut shell liquid. It contains an aromatic ring functionality and has the added advantage of being commercially available (annual production volume of one million tons).

Isocyanate-free Polyurethanes

In both military and industrial applications, there is a need to replace commonly used ingredients that are now recognized to pose a health and/or safety hazard to plant personnel and end users. The use of bisphenol A in can coatings, chromates in protective coatings, and isocyanates as curing agents for PUs are perhaps the three most pertinent examples. Biobased materials have potential utility in the development of alternatives in some cases.

Webster, Mannari, and Soucek have all focused on the development of nonisocyanate curing agents. Webster has been exploring the use of cyclic carbonate derivatives of epoxidized sucrose soyates, which can be cured with amines. The reaction takes place at room temperature, but can also be accelerated with low levels of heat. The rate is dependent on the amine structure, with primary and less-
hindered amines reacting more rapidly than secondary and bulky amines.

Mannari’s solutions involve the use of cyclic carbonates and diamines. “Carbonate-diamine chemistry isn’t new for making polyurethanes, but our approach using cyclic carbonates is customized to ensure that the resultant resins have desirable properties,” he comments. The PUs formed in the reaction are slightly different from conventional PUs in that they possess a b-hydroxy group. The presence of a large number of such polar groups in the cured coating has the potential to impact chemical and alkali resistance and result in higher viscosities due to hydrogen bonding, according to Mannari. While higher viscosities were observed, he did not, however, see as large an impact on coating performance as expected. His group, therefore, investigated the use of different reactive diluents as a means for locking the hydroxyl groups via secondary crosslinking.

Mannari proposed two types of nonisocyanate PUs for aerospace applications—high-solids (> 60% at time of application) and single-component UV-curable solventborne systems with zero HAPs. A total of 28 UV-curable compositions were screened using conventional reactive diluents with a focus on the resultant mechanical and chemical resistance performance. This project, funded by the Strategic Environmental Research Development Program (SERDP), is currently underway, according to Mannari. He is also investigating the possibility of curing these coatings using a UV-LED source.

Soucek elected to focus on the development of waterborne/latex monomers and UV-curable reactive diluents for the formulation of nonisocyanate urethane-modified acrylic latexes containing some acrylate groups. His approach involved modifying the synthesis route used to produce urethane acrylic hybrids, which involves the copolymerization of urethane acrylic monomers and acrylates. To increase the level of incorporation of urethane groups into these polymers, Soucek mixed specially designed UV-curable reactive diluents with the urethane acrylic monomers. The diluents are produced by reacting aliphatic amines with ethylene carbonate to intermediate carbamates that are then reacted with methacrylic anhydride to generate nonisocyanate urethane functional monomers. “With this method, it is possible to add more urethane groups without increasing the formulation viscosity. Simple addition of the new monomer to the latex provides an acrylic urethane dispersion without other processing. In the resin, pendant urethane groups hydrogen bond to increase the T_gĚýof the latex and improve other properties, such as tensile modulus, tensile strength, and storage modulus. At the same time, the phase separation and processing issues observed with most PUDs are alleviated,” Soucek observes.

Chromium Alternative

Corrosion resistance is a primary concern for any applications in which metal substrates may be exposed to harsh environments. Currently, chromium-based pretreatments are commonly used to improve corrosion prevention on aluminum surfaces used in aerospace applications. Because this form of chromium is toxic, there is an urgent desire to replace this pretreatment method with a more sustainable alternative. Mannari has developed organosilane technology that has been customized for use on structural aluminum alloys. The bis-ureasil and epoxy silanes produce stable sol-gel bath compositions that when formulated with nano-silica and organic corrosion inhibitor in varying proportions generate pretreatments that are compatible with topcoats and provide the corrosion resistance, adhesion, and mechanical properties essential for high-performing coating systems. According to Mannari, they provide the same or even greater level of protection afforded by chromate conversion coatings. One difference is the film thickness, which is slightly higher (4–6 vs 2–3 microns, respectively).

Working with Lignin and Cellulose

To overcome the limited availability of biobased raw materials, one approach is to look for sources of biomass that are generated in large quantities as byproducts of other industrial activity. Both lignin and cellulose meet this criterion. Lignin is an important structural component in the cell walls of woody plants. It comprises approximately one-third the mass of lignocellulose, the raw material for papermaking (the remainder is cellulose). In most papermaking processes, the lignin is removed. It is often burned as fuel, but could serve as a raw material for the production of value-added products. Lignin is very difficult to work with, but Webster has discovered a process for functionalizing the material without the need to use any solvents. The product of this fairly green process is a liquid resin that, due to its highly aromatic nature, imparts attractive properties to thermosets.

Pourhashem is also exploring the sustainability of coatings based on lignin. Because it is a byproduct from another industry (paper or biofuel), it could, through its use in coatings, contribute to a circular economy, minimize waste, and essentially improve the efficiency and environmental impact of both the coatings and paper sectors. For a similar reason, she is evaluating coatings made from materials derived from corn and corn cobs.

Minko, in collaboration with Suraj Sharma, associate professor and graduate coordinator in the Department of Textiles, Merchandising and Interiors at the University of Georgia, meanwhile, is investigating the utility of fibrillated nanocellulose, a very strong material with a high elastic modulus that comprises small fibrils of cellulose in the range of 10–100 nanometers that are produced following the chemical or mechanical degradation of plant cells walls in wood pulp traditionally used in papermaking. Due to the decline in the paper industry, wood processors have sought other applications for wood pulp, with the production of nanocellulose one option that is being explored. The material is finding increasing use in the pharmaceutical and packaging industries and in composite applications. The initial product of wood pulp degradation (exposure to high shear rate in a homogenizer) is a hydrogel containing the nanocellulose. Minko’s group is exploring the combination of this hydrogel with other green materials and monomers to form new materials with many potential applications, including high-performance functional textile coatings. “Nanocellulose is valuable because it provides improved mechanical properties while also being biodegradable and sustainable,” Minko says.

To overcome the limited availability Ěýof biobased raw materials, one approach is to look for sources of biomass that are generated in large quantities as byproducts of other industrial activity.

One of the challenges has been improving the water resistance of formulations based on the nanocellulose hydrogel. “Cellulose is hydrophilic; plants use lignin and some waxes to make the plant wall more hydrophobic,” Minko explains. His group has tried to take a similar approach, using natural products wherever possible, but in some cases small quantities of petrochemicals to make the nanocellulose more compatible with hydrophobic materials. In textile coatings, the fibrillated nanocellulose acts as a binder, providing strong adhesion between the cellulose fiber matrix and the functional coating material and ensuring retention of the coating materials on versatile fabric surfaces, according to Minko. “The coatings provide a means for introducing functionalities to textiles that can improve their performance, such as thermal energy management and launderable conductive features, and extend their lifespans,” he adds. One specific project that Minko’s group is working on is the development of novel thermo-regulating textiles material for military uniforms.

Cure-on-Demand

Current cure-on-demand technologies are two-component, UV-, E-beam-, or thermally cured systems, each of which has a problem, according to Soucek.Ěý “Two-component systems in general have limited processing/potlife capabilities. UV has line of sight and opacity issues dictated by Beer’s law, E-beam has safety issues, and thermal curing is not possible for heat-sensitive substrates such as plastics,” he explains.

To overcome these various problems, Soucek has attached a free radical initiator to a magnetic nanoparticle that can initiate polymerization or curing reactions upon oscillation of the nanoparticle and without substantial heating of the coating. “With this approach, heat-sensitive substrates can be coated without line-of-sight issues, while opaque composites and highly pigmented coatings can be cured without being impacted by Beer’s law,” he explains. “This new cure-on-demand technology would augment UV- and E-beam curing of polymeric materials into composites, adhesives, and coatings and may even be useful for in vivo applications such as bone stabilization or cartilage enhancement,” Soucek states.

Modeling to Evaluate Sustainability

One of the challenges for researchers investigating novel materials for the development of sustainable coatings is to understand the actual level of sustainability that a technology achieves when the whole lifecycle is considered. Pourhashem recently joined NDSU and began applying her expertise in modeling of environmental impacts for biofuel production to paints, coatings, polymers, and polymeric materials. “We look at the ingredients in the formulation and the process conditions used to make those ingredients and the coating itself.Ěý In addition, we follow the supply chain back to the basic raw materials that are used and consider all of the inputs and outputs that are involved,” she explains. The results are compared to the performance of competitive products that are already on the market to determine if the new technology is indeed more sustainable. Her analyses are also used to identify areas for improvement and optimization so that the sustainability of new technologies can be enhanced.

The factors Pourhashem considers range from the raw materials—chemicals including solvents, catalysts, and energy used in the form of heat or electricity—to their global warming potential and contribution to ozone depletion, to the toxicity to humans and ecosystems. “We start at the beginning with the extraction of basic raw materials (mining for minerals, oil for petrochemicals, and cultivation for plants) and consider every aspect that could have an impact on the environment to determine how sustainable a coating really is,” she remarks. “What we have found is that in some cases choices that were made with the intent of increasing sustainability may have unintended consequences that, in the end, actually have a negative impact,” Pourhashem adds. An example output is the quantity of fossil fuel consumed to produce a ton of a specific paint or to coat a square meter of surface. This type of result makes it possible to compare the sustainability performance of different coatings.

CoatingsTech | Vol. 16, No. 4 | April 2019