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

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

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

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

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

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

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

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

Q: How do university–industry collaborations accelerate innovation?

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

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

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

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

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

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

Introduction

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

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

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

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

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

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

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

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

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

Introduction

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

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

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

Background

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

FIGURE 1 Cartoon schematic of block resistance.

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

For many years, aqueous hybrid dispersions of poly(vinylidene fluoride) (PVDF) and acrylic resins have been formulated into waterborne topcoats because of their exceptional weatherability and ability to meet stringent volatile organic compound (VOC) requirements and sustainability targets. For applications requiring strong chemical resistance, hydroxy-functional PVDF-acrylic dispersions are available which allow formulators to build resistance properties with isocyanate crosslinking. However, isocyanate not only presents respiratory hazards to paint applicators, but it can cause microfoaming in the resultant films due to CO₂ generation from the reaction of isocyanate with water. Recently, new one-component self-crosslinkable PVDF-acrylic hybrid latexes were successfully developed, and can be formulated below 100 g/L VOC. Detailed properties, such as detergent resistance, chemical resistance, and dirt pick-up resistance, in target applications such as architectural façade coatings and protective coatings are presented.

Introduction

Poly(vinylidene fluoride) (PVDF)-based topcoats¹ have been used for decades on monumental buildings around the world, and they have become the gold standard for decorative property durability and substrate protection. This performance is attributed to PVDF’s outstanding UV and chemical resistance, and its good barrier properties against moisture and oxygen. The superior UV and chemical resistance of PVDF, relative to other common coating polymer chemistries, is demonstrated by its extremely low absorbance in the UV, as can be seen in Figure 1. The UV absorbance spectra were normalized to 25 μm dry film thickness. PVDF copolymer with hexafluoropropylene (HFP) comonomer was used in this study.

FIGURE 1: UV absorbance spectra of PVDF and other polymer chemistries. UV-B band (280-313 nm) from sunlight is highlighted in yellow.

PVDF-based coatings have historically been limited to factory-baked coatings on metal because of the need for a high-temperature bake (230-250 °C) to alloy the polymer components. These baked PVDF coatings, commonly used as topcoat finishes on monumental buildings and other architectural applications, typically contain a blend of 70-80 wt % PVDF resin with 20-30 wt % of a miscible acrylic resin. Around the year 2000, water-based hybrid resin technology became commercially available,² combining PVDF copolymers and acrylic resins in pre-alloyed form.³ The new water-based technology allows for the application of durable PVDF-based coatings under field-applied and low-temperature bake OEM conditions, with dramatically lower levels of emitted volatile organic compounds (VOCs). Figure 2 shows some South Florida weathering panels for a commercial waterborne PVDF-acrylic binder, after 20 years of exposure. Minimal visible differences can be noted between the unexposed and exposed areas of the panels.

FIGURE 2: Twenty years’ South Florida field exposure weathering panels of one-component PVDF-acrylic-based waterborne coatings (as shown in left for each color) vs legacy solventborne baked PVDF-acrylic coatings (right for each color). Panels are exposed at 45° South-facing. The substrates of these panels are chromated aluminum Q-Panels (AL-412 from Q-Lab Corporation).

More recently, hydroxyl-functional PVDFacrylic hybrid products in this class were developed, which could be used with crosslinkers such as water-reducible polyisocyanates.^4,5 These systems show enhancements in certain key properties such as early hardness, barrier properties, solvent resistance, and adhesion, with performance contributions coming both from the entangled polymer network and from the network formed by crosslinking reactions.⁶

However, similar to other two-component systems with isocyanate crosslinking, isocyanate not only poses respiratory hazards and carcinogenic potential to paint applicators, but it can also cause microfoaming in the resultant films due to CO₂ generation from the reaction of isocyanate with water in the paints. This is particularly noticeable when applying paint with a brush or roller outdoors (Figure 3).

FIGURE 3: Microfoaming issue with two-component waterborne paint with isocyanate crosslinking.

In this article, we present studies for developing a one-component selfcrosslinkable PVDF-acrylic hybrid latex and waterborne formulations based on this hybrid latex for architectural façade coatings and protective coatings.

Experimental

Synthesis of Self-crosslinkable PVDF-acrylic Hybrid Latex

A two-stage process was used to make the PVDF-acrylic hybrid latex.^7,8 PVDF latex was made in the first stage through emulsion polymerization of vinylidene difluoride monomer and an optional HFP comonomer in a pressure reactor. The second stage of the polymerization process, also called the acrylation stage, incorporated the acrylic monomers into PVDF latex to produce the intimate micromolecular mixture of PVDF and acrylic polymers. A wide variety of acrylic monomers with different T_g and functionalities can be chosen to tailor the coatings properties to the desired requirements. In this work, diacetone acrylamide (DAAM) monomer was introduced into the PVDF-acrylic hybrid latex along with other acrylic monomers and was copolymerized within the acrylic copolymers, creating well-dispersed pendant ketone crosslinking sites. Adipic dihydrazide (ADH) acted as a difunctional crosslinking agent, remaining partitioned in the water phase outside of the emulsion particles. ADH could be either added to the latex after emulsion polymerization was complete or during the paint formulation stage. Acrylic emulsions based on DAAM with ADH were initially nonreactive, ensuring emulsions maintained good long-term stability during shipping and storage. One-component keto-hydrazide self-crosslinking can occur at ambient temperature, facilitated by water evaporation during the film drying process and a simultaneous reduction in pH resulting from the loss of ammonia (a neutralization agent added in emulsion polymerization and paint formulation) (Scheme 1).

SCHEME 1: Keto-hydrazide self-crosslinking mechanism. P denotes the polymer chain.

Microbial contamination on surfaces is a problematic and potentially deadly issue, particularly in high-risk settings such as healthcare, aged care, and food and beverage. In this research, we present an antimicrobial waterborne polyurethane additive that will be of interest to the coatings community due to its high compatibility with a variety of coating systems, which results in a range of highly diverse and useful applications.

This next-generation antimicrobial uses a nano-composite approach to create a silver-based active ingredient that is non-toxic and truly non-leaching. The presented technology produces strong binding between silver and the polymer backbone. This prevents leaching while retaining high activity with proven results against a range of pathogens.

Introduction

Each day, approximately 1 in 31 U.S. hospital patients and 1 in 43 nursing home residents contract at least one infection associated with their healthcare.¹ Healthcare-associated infections accrue direct costs to U.S. hospitals of at least $28.4 billion each year.² Healthcare settings are just one example of a high-risk area where the transmission of disease is dangerous and expensive.

Silver is well known for its excellent antimicrobial properties, and many products have been produced that exploit this.^3-5 These products typically work via the controlled release of silver ions or nanoparticles, resulting in concerns over the release of silver into the environment and the interactions it subsequently undergoes.^6-8

Countering this risk, a novel process has been developed that binds the silver active ingredient directly to a polymer backbone, creating a nanocomposite from which the silver does not leach.^9,10 This produces an antimicrobial material that is not only sustainable and environmentally friendly, but also displays incredible longevity as the active ingredient is not depleted.

In this research, a water-based silver-polyurethane nanocomposite material has been developed that displays antimicrobial activity against bacteria, viruses, and fungi. Its high potency means it can be utilized as an additive in other coating systems, and its compatibility with a range of materials has been shown, including acrylates, polyurethanes, and other waterborne systems.

As a result, this antimicrobial additive can be used effectively in a range of highly diverse applications (textiles, walls and floors, furniture, high-touch surfaces, filters, etc.).

Experimental

The silver-polyurethane composite was produced using Inhibit Coatings’ proprietary functionalization process.

Characterization

X-ray diffraction (XRD) was used to confirm the crystalline structure and composition of the silver particles within the polymer. A PANalytical X’Pert PRO diffractometer was utilized with a copper K-alpha X-ray source at a wavelength of 1.5405 Å, operating at 45 kV and 40 mA.

A JEOL 2010 transmission electron microscope (TEM), operated at 200 kV, was used to visualize the silver particles within the polymer. The silver-polyurethane composite was diluted and then drop cast onto 200 mesh copper grids and plasma treated with a JEOL EC-52000IC ion cleaner prior to TEM analysis.

Independent Testing

Antimicrobial Testing

Antibacterial testing of the silver-polyurethane composite applied to a polyester textile was conducted according with the AATCC 100-2019 standard¹¹ by Microbe Investigations Switzerland (MIS). The sample was tested against Escherichia coli (E. coli) (ATCC 8739) for a contact time of 24 hours.

Antiviral testing of the silver-polyurethane composite in a polyurethane coating on acrylic was conducted according to the Japanese Industrial Standard JIS Z 2801 standard (modified for viruses)¹² by Microchem Laboratory. The sample was tested against Human coronavirus (ATCC VR-740, Strain: 229E) and Influenza A virus (H1N1) (ATCC VR-1469, Strain: A/PR/8/34), for a contact time of 2 hours.

Antifungal testing of the silver-polyurethane composite in a polyurethane coating on acrylic was conducted according to the ASTM G21 standard¹³ by Microbe Investigations Switzerland (MIS). The test details utilised are provided in Table 1.

Leach Testing

Leaching of silver from the silver-polyurethane composite was conducted by Nanosafe, Inc. Testing of the composite applied to fabric samples followed U.S. EPA Method 1311 “Toxicity Characteristic Leaching Procedure,”¹⁴ adapted for the assessment of silver-leaching potential from textiles.¹⁵ Testing of the composite applied to wood samples was conducted under guidance of OECD 313 “Estimation of Emissions from Preservative-Treated Wood to the Environment.”¹⁶

Toxicology Testing

Toxicology testing, as outlined in Table 2, was conducted by STILLMEADOW, Inc., on the silver-polyurethane composite.

Preservative Testing

Preservative testing was run using a Difco Paddle Tester over three weeks, using three concentrations of the silver-polyurethane composite in a polyurethane dispersion, and testing weekly for bacterial growth.

Results and Discussion

Silver Particle Characterization

Characterization techniques have verified that metallic silver nanoparticles have formed.

The XRD pattern of the silver-polyurethane composite has shown peaks with 2θ values of 38.2°, 44.3°, 64.5°, and 77.6° (Figure 1), which can be attributed to the (111), (200), (220), and (311) crystallographic planes of face-centered cubic (fcc) silver crystals, respectively.¹⁷

������Mary C. Chervenak,��Donovan Lujan, and Jeffrey Arendt Arkema Inc.

Although exterior architectural coatings improve the appearance of a structure, they are ultimately intended to be protective, preserving the integrity of a substrate by isolating it from environmental exposure. As the regulatory landscape shifts, however, coating composition is becoming equal in importance to coating performance. Perfluoroalkyl substances (PFAS), defined in a 2022 Organization for Economic Co-operation and Development (OECD) report as “fluorinated substances that contain at least one fully-fluorinated methyl or methylene carbon atom (without any H/Cl/Br/I atom attached to it),” are an effective tool for improving flow, gloss, adhesion, and water- and stain-resistance of coatings, but their use has a negative impact on both human health and the environment. Eliminating PFAS, while maintaining coating performance, requires unique binder chemistry that is both flexible and durable. An all-acrylic waterborne latex for exterior architectural applications has been engineered without PFAS. This new, low-coalescent demand binder has improved surfactant leach resistance when compared to a similar PFAS-containing product, while maintaining other performance properties, such as block resistance and dirt pick-up resistance. Through creative polymer design, a more ecologically sound waterborne all-acrylic latex with improved exterior performance is possible.

Introduction

Although liquid suspensions of pigment were first used more than 30,000 years ago in a decorative capacity, the utility of paint as protection was not fully realized until the dawn of the Industrial Revolution, when the first paint and varnish factories began mass-production of readymade coatings.¹ While the automotive industry introduced the need for anti-corrosive coatings, special-purpose coatings were eventually developed for other products and industries, including farm equipment, children’s toys, furniture, and food production.² Historically, in addition to innovation, the coatings industry has recognized and responded to potential negative impacts of product chemistries on human health and the surrounding environment. For example, during the years leading up to World War II, as consumers began to fully comprehend the inherent health and environmental risks associated with a common paint ingredient, lead, paint manufacturers ultimately found a safer alternative, titanium dioxide. The use of lead pigments in consumer paints was limited in the United States by the 1950s and fully banned in 1978.³

As academic institutions, governmental agencies, corporations, and consumer groups began to acknowledge the extent of coatings’ impact on the environment in the early part of the 21^st century, demand increased for eco-friendly solutions that both comply with environmental regulations and maintain product performance. Coating manufacturers first met these calls for change by either reducing or eliminating volatile organic compounds (VOCs) in solvent-based and water-based coating formulations, but recent regulatory developments and industry trends have led to more aggressive measures to reduce industrial environmental footprints.^4,5 To continue to expand this $26.1 billion industry, development of new, high-performance coatings and a commitment to sustainable chemistry and manufacturing practices is now paramount.⁶

In February 2021, the U.S. Environmental Protection Agency (EPA) began developing the Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) to provide new data on 29 perfluoroalkyl substances (PFAS) and to clarify their impact on community drinking water. Since then, the EPA Council of PFAS has been created to better understand, and ultimately reduce, the potential risks of PFAS. EPA has also released preliminary Toxic Release Inventory (TRI) data, enhanced TRI reporting requirements, and begun development of a national testing strategy for PFAS. Additionally, in June 2022, EPA released four drinking water health advisories for PFAS; as a direct result, $1 billion in Infrastructure Law grant funding has become available to address PFAS contaminants in drinking water. More recently, in January 2023, EPA proposed a rule that would prevent starting or resuming the manufacture, processing, or use of an estimated 300 PFAS that have not been made or used for many years, known as “inactive PFAS,” without a complete EPA review and risk determination.⁷

Earlier generations of acrylic latexes were created with the intention of meeting the consumer expectation that a fully formulated coating would contain no more than 50 g/L volatile organic content (VOC). Reduced VOC targets were readily met by latexes having lower glass transition (T_g) temperatures and minimum film-forming temperatures (MFFT), but their use resulted in softer films. Softer films were deficient in several performance areas, including surface feel, dirt pick-up resistance, block resistance, and stain removal. Surfactant leaching was also observed. Surfactant leaching is defined as the unsightly staining caused by coating components migrating through the film and streaking down the coated surface. This defect is unique to lower-VOC exterior coatings, particularly when a deep tint coating is applied in low-temperature and high-humidity environments.

Improved surfactant leach resistance was identified as a product improvement target. Built on an exterior acrylic platform recognized for its durability and color acceptance, a new polymer was designed specifically to resist surfactant leaching. While surfactant leach resistance was successfully achieved through polymer design, certain performance properties were compromised. Block resistance, in particular, was found to be deficient. Performance improvement was realized, in part, through the incorporation of a specific class of PFAS, fluoropolymers, into the polymer recipe. Fluoropolymers have non-wetting and non-sticking properties, and are a well-established way to introduce block resistance.⁸ The release of the PFAS Strategic Roadmap by EPA in October 2021, however, indicated a dramatic shift in the regulatory landscape.⁹ In response, an improved exterior all-acrylic latex produced was developed to exceed the performance of its PFAS-containing predecessor, without the incorporation of PFAS.

Introduction

The coatings industry has undergone significant transformations in recent years due to the replacement of organic solvent-based coatings by waterborne emulsion latex polymer coatings. Waterborne technology has generated profound impact in industry and everyday life, producing great environmental and health benefits. The prevalence of volatile organic compounds (VOCs) in coatings has been greatly reduced, from 700 g/L in the 1940s to ∼ 50 g/L in the 2010s.¹ Although waterborne coatings offer considerable benefits, challenges remain in areas such as water resistance, stability, film formation, and surface hardness, which can affect their overall performance and application.

These challenges are primarily caused by the conflicting requirements for desired properties before and after the coating dries. To maintain a stable dispersion before application, latex particles should be fully dispersible in water, i.e., hydrophilic. However, after the coating dries, water repellence, or hydrophobicity, is required. Thus, a solution that can maintain predominantly hydrophilic dispersion while rendering a hydrophobic surface after drying is necessary to make waterborne coating technology more versatile. In addition, a durable coating film demands excellent adhesion on the substrate surface, while showing good hardness (low tackiness) at the coating-air interface. This means it is beneficial to possess different or even opposite properties on the two sides of the coating films.

One approach to combine these different properties is to apply multiple coats. It is common practice to coat primers as the first layer to provide good adhesion. After the primer is dried, a topcoat is then applied to afford more desirable surface properties. However, this approach consumes extra material, time, and effort. For applications that require both performance and fast turn-around, such as traffic coating, a simple one coat solution is strongly preferred. Another grand challenge in waterborne coating materials is to eliminate VOCs and create a “zero-VOC” paint. Such coatings will further benefit environmental and consumer health. However, removing all the VOCs will make it difficult for latex particles to form an integral coating film unless the glass transition temperature (T_g) for polymer binder is greatly reduced. This can be done by altering the polymer chemistry or adding non-evaporative coalescent molecules, however doing so will inevitably hurt coating hardness and many other properties. Therefore, technology that can guarantee film formation while providing a hard coating surface becomes the holy grail in coating research. Most ideas have been developed around two-component (2K) systems and crosslinking chemistry, which are usually much more costly and require more complicated chemistry and formulation.

In this article, we report on an innovative coating additive, Janus particles, which can significantly modify the surface properties of a waterborne coating system while leaving the bulk of its properties mostly intact. As shown in Figure 1, Janus is the name of an ancient Roman god who has two faces. Janus particles are particles that possess two different chemical make-ups, often with contrasting properties, on each side of a single particle. For example, an amphiphilic Janus particle has one hydrophilic side and one hydrophobic side, which can also be viewed as a colloidal version of a small surfactant molecule. Although Janus particles have not yet been widely used in industry, they have been studied and developed in academia for more than 30 years.

Hosted by the University of Southern Mississippi (USM) School of Polymer Science and Engineering, the Waterborne Symposium offered attendees five days of short courses, technical presentations, a poster session, and in-person networking opportunities.

Three days of optional short courses kicked off the week, leading up to the opening of the symposium on Wednesday, when Juliane P. Santos of Indorama Ventures presented the plenary lecture, “Sustainability Guiding New Developments in the Coatings Industry.”

Santos holds a Ph.D. in Langmuir Blodgett-Films from the University of Sao Paulo. She did her postdoctoral work on synthesis, structure, and properties of latexes at University of Campinas, and she has been working in latex field for 22 years. She is currently a specialist at Indorama Ventures, formerly Oxiteno, where she is responsible for developing surfactants for emulsion polymerization and emulsification of resins.

Following Santos’s presentation, attendees gathered for coffee and networking in the Technology Showcase exhibit hall, where nearly 20 leading suppliers to the industry, including CoatingsTech, offered a firsthand look at related products, equipment, services, and expertise.

After the morning break, Matthew Gadman of King Industries presented the Sidney Lauren Memorial Lecture, “Formulating Durable Aminoplast and NCO Crosslinked Waterborne Coatings: Importance of Backbone Composition.”

The Sidney Lauren Memorial Lecture is a staple of the symposium that memorializes Sidney Lauren, a scientific leader in the coatings industry who served as executive director of the Coatings Research Group and was active in the Coatings Industry Education Foundation, which supported educational programs and curriculums devoted to the sciences of coatings technology.

In 2022, Gadman received the Siltech Best Paper Award for his presentation, which was published in the of CoatingsTech.

Following the opening lectures, the technical presentations split into tracks—Additives, General, High-Solids, and Waterborne—for the remainder of the event. Organizers report that among the 40 presentations, 28 papers were presented.

At the conclusion of the conference, four presenters were recognized for their papers’ exceptional contributions to the technical program. Top honors for the Siltech Best Paper Award went to Shan Jiang from Iowa State University for his presentation, “Creating Waterborne Self-Stratified Coatings by Adding Anisotropic Particles.”

Earning the PCI Award for Technical Excellence was Sebastian Weiss from BYK-Chemie for his paper “Encapsulation of Silicone Additives for Increased Compatibility and Long-Term Effects.”

Two students tied for the Mendon Best Student Paper Award: Aynslie Fritz and Lina Ghambari–both from the Wiggins Research Group at USM.

Other students from USM and Louisiana State University (LSU) also participated in the event, sharing their research with attendees during the 2023 Evonik Student Poster Session that featured 20 student posters.

Andrew Barbour of Qiang Research Group at USM took first place in undergraduate category for “Ordered Mesoporous Carbon (OMC),” while Jaylin Davis of the Patton Research Group at USM “Synthesis and Characterization of Novel Polybenzoxazine Vitrimer Thermosets” was honored for first place for graduate student poster.

Second place for the graduate student posters went to Jacob Schekman of Simon and Nazarenko Research Groups at USM for “Investigating Solvent Effects on thiol-ene Network Formation.”

Two graduate posters tied for third place: Pritha Bhunia Patton Research Group at USM for “Design and Synthesis of Vitrimer Thermosets Derived from Main-Chain Benzoxazine Polyesters” and Maria Martinez of the Pojman Research Group at LSU for “Optimization of Cure-On Demand Thin Layer Coatings Using Frontal Polymerization.”

As a crucial component of the USM academic program, the Waterborne Symposium plays a central role in supplying the industry with qualified candidates to fill technical positions. Proceeds help the university recruit and retain students who show promise as future coatings industry innovators, supporting graduate student stipends and undergraduate student scholarships, acquisition and maintenance of equipment, and more.

The 51st Waterborne Symposium will be held February 4–9, 2024. USM says the abstract submissions will open later this year. For more information about categories of interest and how to submit, visit the Waterborne Symposium website.

Introduction

With the enactment of the Clean Air Act of 1970, the use of waterborne coatings began to increase; however, the high surface tension of water (72 mN/m) required the addition of surfactants to enable water-based coatings to wet most substrates, many of which have surface energies below 50 mN/m. Most surfactants available at that time were primarily designed for use in detergents, cleaners, and emulsion polymerization; while they could lower the equilibrium surface tension of waterborne coatings, these products tended to stabilize foam and could not maintain low surface tension when the coatings were applied under dynamic conditions.¹ Thus, the need for low-foam dynamic wetting agents emerged to facilitate the transformation from solvent-based to waterborne coatings.

The earliest low-foam dynamic wetting agents were based on acetylenic diol chemistry.^1-4 These surfactants’ chemical structures differ significantly from those of most traditional surfactants. To achieve excellent dynamic wetting, these molecules need to be able to move quickly to newly created interfaces. This requires the surfactants to be lower in molecular weight and to have hydrophobic groups that prevent strong micelle formation or interaction with other components of the coating formulation.

Subsequent research and development produced additional non-acetylenic low-foam dynamic wetting agents, but they also had relatively low molecular weights and short, often branched, hydrophobes.^5-10 Such structures appear to be necessary for achieving the required coatings properties, yet their low molecular weights preclude these substances from meeting the United States Environmental Protection Agency (U.S. EPA) definition of low-risk polymer under the Toxic Substances Control Act (TSCA). As a result, significant (potentially prohibitive) time and testing costs are likely to be required to register a new dynamic wetting agent in the United States or other countries with similar inventories.

During the 1970s through the 1990s, it became apparent that many surfactants that performed well in their intended applications had the potential for adverse environmental, health, and safety (EH&S) effects. Several surfactants were found to have reached high levels in waterways, persist in the environment due to slow or minimal biodegradation, harm or kill aquatic organisms, or have the potential to be endocrine disruptors. Therefore, regulatory agencies began to require more diligent assessments of new chemicals and particular attention began to be paid to those with the potential to have adverse effects on aquatic life.

In 1981, the U.S. EPA began using quantitative structure-activity relationships (QSARs) to model chemicals’ potential ecotoxicity behavior. The U.S. EPA and Syracuse Research Corporation then worked together to develop computerized versions of these models known as the Estimation Programs Interface Suite™ for Microsoft® Windows (EPI Suite™), which the Office of Pollution Prevention and Toxics (OPPT) relies upon for risk assessment development when actual data are lacking. These models can be downloaded from the U.S. EPA’s website,¹¹ and regulatory experts may use them to better understand how the EPA might view a new substance’s risk profile in the absence of data. The first version of the EPI Suite™ provided estimated physical, chemical, and environmental properties based upon the simplified molecular input line entry system (SMILES) notation for a molecular structure, and the current version, EPI Suite™ v4.11, provides similar information using improved models.

Once EPI Suite™ became available, the Product Safety group within what has now become part of Evonik’s Specialty Additives division began to use the new tool to understand how the U.S. EPA might view the hazards of the chemicals they evaluated using these models. Initially, comparisons between predicted and actual ecotoxicity data for existing chemicals were made. However, it was soon realized that there was also the opportunity to use EPI Suite™ to predict the ecotoxicity profile of experimental prototypes. Over the next few years, it became clear that surfactants predicted to have superior environmental profiles (i.e., faster, more complete biodegradation and less toxicity to aquatic organisms) required less time and money to register in the United States and Japan than those with potential EH&S red flags. Therefore, changes were made to the company’s new product development work process to reduce both the time and cost required to develop and commercialize new substances, including new low-foam dynamic wetting agents, in the future.

Continue reading in the of CoatingsTech.

When the symposium began in 1973, the world looked very different. That year, the Vietnam War ended, the predecessor to the European Union was formed, and The Godfather won Best Picture at the Academy Awards. A man made the first mobile phone call, and Chicago’s Sears Tower became the world’s tallest building.

The inaugural Waterborne Symposium was also quite different with 135 attendees and seven presentations. In contrast, the 2022 symposium had 230 attendees and 39 presentations, and at its peak in 1998, 507 people attended and 44 papers were presented. Union Carbide and Shell Chemical Company presented at the 1973 symposium. The papers presented included “contributions from scientists from Union Carbide; American Cyanamid Company; DeSoto, Inc.; Lehigh University; and University of Houston.”

Each symposium is the product of 50 years of changes and improvements—evidence of the effort that the Waterborne Symposium’s organizers have made to grow the event and respond to the changes that are inevitable as time passes. Historical events and expansion in the coatings industry have had roles in the symposium’s history, to name a couple.

The September 2001 terrorist attacks resulted in travel restrictions, which severely reduced attendance at the 2002 symposium. Several years later, in August 2005, Hurricane Katrina devastated New Orleans, raising concern that the city would be unable to recover before the next symposium. The city did recover, and the 33rd symposium was held as scheduled in February 2006. More recently, the symposium reinvented itself into a successful virtual event in 2021 because of the COVID-19 pandemic. Although the interactive online event was well-received, attendees welcomed the opportunity to connect in person when the symposium returned to the Crescent City in 2022.

Much of the attention early on sought to refine the various timing logistics of the symposium. The 1973 symposium was held Monday, August 13, through Wednesday, August 15, at the Sheraton-Charles Hotel, but since 1974, the symposium has almost always been held in the winter just before Mardi Gras. In 1985, the symposium schedule shifted to start on Wednesday and end on Friday. That left Monday and Tuesday open for the addition of short courses in 1998, which also saw the implementation of the first Technology Showcase.

The amount of content and resources available to symposium-goers increased substantially when the short courses and Technology Showcase joined the lineup. The Technology Showcase, an exhibition of interactive booths, enables industry experts (that is, scientists and engineers who represent manufacturers, suppliers, and service providers) to present their latest findings and developments.

To accommodate the evolving coatings industry, the Waterborne Symposium has had five names over its 50 years. The first was called the Water-Borne and Higher-Solids Coatings Symposium, but it was changed in 1990 to add “Powder Coatings” because of the growth of that sector. In 1994, “Water-borne” became “Waterborne” to keep up with the times, and in 1995, “Higher- Solids” became “High-Solids.” The final change happened in 1996; because the symposium had expanded to a worldwide audience, the name was altered to start with “International.” By 2007, the International Waterborne, High-Solids, and Powder Coatings Symposium had become inclusive, but a bit long, so “The Waterborne Symposium” became its nickname for branding purposes.

The Waterborne Symposium has remained the same in several aspects. Three faculty members from the Department of Polymer Science at the University of Southern Mississippi (USM) founded the symposium, and USM has sponsored it ever since. The Southern Society for Coatings Technology (SSTC), which cosponsored the symposium from its inception until 1997, switched to sponsoring the newly created Technology Showcase in 1998.

The impact of the Waterborne Symposium should not be overlooked. Its Proceedings publication has been an “important technical resource within the published literature in the field of paints and coatings” for the past 50 years. The European Coatings Journal review deemed the symposium as “North America’s most prestigious conference in the field of paints and coatings” in its March 1999 issue.

Proceeds from the symposium have funded recruitment, scholarships, and program support for the University of Southern Mississippi, which has conferred “approximately 700 undergraduate and graduate degrees in Polymer Science and Polymer Science and Engineering.”

Professors Gary Wildman, George Bufkin, and Shelby Thames founded the Waterborne Symposium with the intention of gathering those in the coatings industry to exchange information and network at an annual technical conference. The symposium has successfully fulfilled—and exceeded—this mission for the past 50 years, as it is now a cornerstone of the paint and coatings industry.

Be sure to check out the entire digital issue of the January-February 2023 CoatingsTech.