Graphene in Coatings: Overcoming the Challenges to Reap the Benefits
Although graphene comprises a one-atom-thick layer of carbon atoms in its ultimate form to nanoplatelets with multiple morphologies, the arrangement of the carbon atoms in that layered material imparts incredible strength as well as the ability to efficiently conduct heat and electricity in a transparent system with unique optical properties. Not surprisingly, interest in graphene has been high since its discovery in 2004, and significant progress has been made in developing commercially viable production methods and applications. According to a June Graphene Commercialization Update by The Graphene Council,1 over 2,300 graphene-related patents have been granted, mostly to companies and academic institutions, and graphene is predicted to impact more than 45 industry sectors and applications, with the top areas including energy storage, semiconductors, composites/plastics/polymers, advanced materials, metals, chemicals, display electronics, bulk manufacturing, sensors, and healthcare. Notably, the graphene market is maturing, with mainstream companies becoming increasingly involved and a greater percentage of patents relating to higher-
value applications rather than graphene production. Several companies are now able to produce up to tons of graphene with batch-to-batch repeatability, with chemical vapor deposition allowing larger formats and quantities at lower prices. Sourcing of raw materials has expanded from graphite mining to include by-products of bio-diesel production and other organic sources such as hemp. Concerns about the safety of graphene are also being addressed, enabling wider adoption of this unusual material.
Both the aerospace and automobile industries present numerous opportunities for graphene use.
Both the aerospace and automobile industries present numerous opportunities for graphene use. In the former, it may be valuable in lightweighting, energy storage, de-icing and lightning strike protection, among other applications, not only for civilian and military aircraft, but also unmanned vehicles, spacecraft, and satellites. There are many exterior and interior automotive applications for graphene, including coatings, electro-magnetic interference shielding, thermal management, light weighting, sensors, improved road tires, composite strengthening, and energy storage functions. There has already been commercial adoption of graphene-modified polyurethane foams, adhesives, batteries, and under-the-hood parts. Interest in other sectors is also growing, although education is needed to improve end user understanding of differences between graphene material types and graphene producers. The Graphene Council predicts that the most successful graphene manufacturers will pursue at least some level of vertical integration, offering not only graphene powder, but value-added intermediary products and, in some cases, fully integrated solutions. Those companies that invest in market development/sales efforts, particularly close customer engagement, co-development and education efforts, will convert interest into demand.
Adding graphene to coating formulations can have multiple effects on the performance of the resulting applied films. Perhaps most notably, adding graphene to coatings has the potential to increase resistance to water, oxygen and other oxidizing agents, scratching and abrasion, the growth or organisms including barnacles in the ocean and bacteria in homes and hospitals, and electromagnetic waves; impart electrical and thermal conductivity; and increase adhesion or provide a hydrophobic effect depending on the application.
Some of the earliest graphene-containing coatings to reach the market have targeted the automotive sector, where it competes with ceramic coatings for automotive refinish applications. Unlike ceramic coatings, which retain heat and hold on to water droplets, coatings containing graphene dissipate heat and have high water contact angles. As a result, graphene coatings do not suffer from water spot formation and have improved stain and abrasion resistance. Their anti-static properties help reduce dust buildup as well. Graphene thus allows for easier cleaning and also provides a wet, glossy look with enhanced reflectivity and anti-fouling and UV resistance properties. One negative of graphene-containing coatings compared to ceramic coatings is their higher upfront cost, which keeps some auto detailers on the sidelines as they wait to see whether their performance is worth the cost. Prices are coming down, though. Three examples of manufacturers of automotive graphene-based coatings include Surface Protective Solutions (SPS Graphene), Ethos Car Care (Graphene Matrix), and Artdeshine (Nano Graphene Coating).
One of the coating application areas receiving the greatest interest today is for corrosion protection. When appropriately incorporated into either solvent or water-based coatings, graphene can impart exceptional anti-corrosion performance and enhanced corrosion control for asset life extension, maintenance cost reduction, and more sustainable protection solutions, according to Adrian Potts, chief executive officer, Applied Graphene Materials (AGM), a manufacturer of graphene and value-added graphene products. The anticorrosion performance of graphene is believed to occur via a combination of physiochemical activity involving the restriction of water, oxygen, and salt uptake along with electrochemical activity dependent on loading and substrate. Based on electrochemical studies carried out at AGM, graphene appears only to be electrochemically active on metals high on the electrochemical series. It is known that plate-like glass flakes and micas act as barrier pigments, providing a tortuous path in corrosion-inhibiting primers, according to Potts. “With their high aspect ratio, high surface area, and low density, when correctly dispersed within a coating, graphene nanoplatelets can enhance substantially the barrier performance of a given thickness of coating, acting as a super-efficient additive and offering even more protection,” he asserts. Depending on formulation specifics, a range of other benefits can also potentially be imparted using graphene nanoplatelets—for example, anti-static capabilities arising as a result of the electrical conductivity of the material. “All this we see can be achieved without a substantive change to mechanicals such as flexibility in carefully formulated systems,” Potts observes. He also points to the extremely low loadings employed with some of AGM’s graphene dispersion as making them cost-effective solutions for enabling some remarkable performance gains as an anti-corrosion additive.
The challenges to adding graphene to coating formulations can be quite complex, however. It is most important, according to Potts, to avoid adding graphene in powder form because it has a natural tendence to agglomerate. “One of the fundamentals is to deliver the graphene nanoplatelet powder to a coatings formulation in a way that is easy to use and effective in achieving the end goal—which simply put is achieving as excellent a spacial distribution of individual nanoplatelets in the finished coating as possible,” he explains. “The best solution is to present the graphene in a component of the final formulation such that the materials can be easily integrated,” Potts adds. That is why AGM supplies its graphenes for liquid resin applications in easy-to-use, stable dispersions in commonly used solvents, resins, and water. Custom solutions can also be prepared to suit specific customer chemistries. AGM has, in fact, spent significant effort to understand how to best integrate its dispersions, such as at the grind vs let-down stage, and provides this information in its technical application notes. “Having the best dispersions and the knowhow on how to employ them is pretty significant in enabling good results for a range of formulations,” he says. As a result, understanding a customer’s coating formulation is also key to successful application of a graphene dispersion to achieve positive end performance. “Engaging with customers is important to enable successful outcomes; the more information we are able to share, the more likely a successful outcome will be,” Potts concludes.
One of the fundamentals is to deliver the graphene nanoplatelet powder to a coatings formulation in a way that is easy to use and effective in achieving the end goal.
Safety is also an important consideration when working with novel nanomaterials, including dispersions of graphene nanoplatelets. “At AGM, we pride ourselves on de-risking the customer experience. We have done extensive testing to support a clear understanding of what happens to this material during spray application events, for example. As a result, ample guidance is available to demonstrate safe use,” Potts comments.
AGM has also subjected various starting point coating formulations containing its graphene dispersions to extensive accelerated testing, often to many thousands of hours. These studies have demonstrated that corrosion can be dramatically slowed in steel and aluminum using a carefully formulated graphene in a coatings system, according to Potts. “Clearly, the hard miles have been travelled for generic, easy-to-use graphene dispersions for coatings applicability with extremely good effect. We are able to cater to a range of potential applications from general industrial protective coatings through C4 and C5 high-performance applications,” he notes. The graphene dispersions AGM offers, Potts adds, can be formulated into primers, tie-coats, and topcoats (where color permits) with extremely low solids additions. AGM has also demonstrated good performance through selective reduction of zinc phosphate actives in primers with graphenes and, in some cases, the addition of non-metal actives to create hybrid additive dispersions.
A number of AGM customers have launched graphene-containing protective coatings formulations, including Alltimes Coatings and Blocksil, which target the construction industry. Alltimes has even crafted a CPD for architects to enable its systems to be specified with confidence alongside the extended warrantee for the Advantage Graphene system that they offer. AGM also has customers with products in the auto repair and aerospace markets. In the latter, graphene has been incorporated into coatings for composites to improve the performance of carbon fiber pressure vessels. “Commercial momentum is increasing across a range of industry sectors, and we are looking forward to volume increases as the industry returns post-coronavirus,” Potts notes.
Other companies offering graphene-containing protective coatings include TBA Protective Solutions, with clear, conductive, water-based epoxy, flexible polyurethane, and aerosol acrylic paints. The Global Graphene Group offers thermal paints, conductive coatings and inks, and anti-corrosion coatings (primer and mid-coat) containing graphene. Perth, Australia-based Talga, which produces battery anodes and graphene, has developed a graphene additive for marine coatings that is intended to improve corrosion resistance, decrease metallic paint loss into oceanic ecosystems, and afford better productivity through lengthened drydocking cycles.2 The dispersible additive can be incorporated into coatings on-site. The company is currently conducting two large-scale commercial trials on two commercial ship hulls over a 12- to 18-month period. In the first test, the Talcoat additive was mixed into AkzoNobel’s two-part epoxy Intershield 300 prior to distribution to the ship management company for application on a container ship. In the second trial, the additive was mixed into another leading two-part epoxy marine coating from a different supplier at the drydock by the paint applicators before spray application to a second container ship during drydocking.
At least one graphene-based coating line for architectural applications is on the market today. Developed by Antonio León Jiménez and sold by the Spanish company Graphenestone, the range of Graphenestone paints containing graphene includes lime-based products for both exterior (Biosphere) and interior (Ecosphere) applications, one of which is a photocatalytic paint (AmbientPro+) that also contains titanium dioxide nanoparticles that decompose organic compounds and inorganic gases in the presence of natural and artificial light. The company also offers an acrylic-based conductive coating (Proshield) containing graphene that is designed for protection against high- and low-frequency electromagnetic radiation.
Graphene-containing coatings may also help in the fight against COVID-19. New York-based vertically integrated graphene producer GrapheneCA is focused on developing eco-friendly and cost-conscious graphene solutions that are scalable and commercially viable, including products for use in the construction, medical, cosmetics, and coating industries. In May, the company announced that its Dr. Nano Flooring and Dr. Metal coatings have demonstrated in an independent laboratory test exceptional activity against gram-positive and gram-negative, antibiotic-resistant bacteria that can cause severe respiratory infections, among other things.3 The proprietary formula in the graphene-improved, water-based epoxy coatings blocks the metabolism of microorganisms by restricting cellular respiration and cell division on surfaces, according to the company. GrapheneCA is in the process of validating its findings against viruses and other micro-organisms, and looks forward to starting discussions with commercial partners for manufacturing and shipping soon after, according to Sergey Voskresensky, head of research and development at the company.4 “Our mission is to provide protection to the concentrated areas that are most vulnerable to spreading viruses and other micro-organisms,” he noted.
Clearly, multiple opportunities exist where coatings formulators have a desire to extend performance of their systems with innovative technology, and graphene materials can offer significant performance advantage in the more aggressive environments that coatings routinely have to survive, according to Potts. “With the longevity, durability, and corrosion mitigation advantages that graphene has to offer, there’s a significant number of opportunities that this technology can be applied to, whether offshore or on land, or indeed in space applications,” he comments. Broad opportunities also exist in the powder coatings space. Once again, careful selection of the additive media to conform to the requirements of the powder coating manufacture process is essential for success, according to Potts. “If graphene can be dispersed well, then it can be added at the right stage to current powder coating processes to achieve well-dispersed arrays of nanoplatelets in the end products,” he says.
- Barkan, T. and Johnson, D. “Graphene Commercialization Update,” Presentation by The Graphene Council, June 25, 2020.
- PCE International, “Graphene goes to sea,” Global Newswire, April 16, 2020. https://www.pce-international.com/2020/04/16/graphene-goes-to-sea/ (accessed September 10, 2020).
- GrapheneCA, “GrapheneCA’s Breakthrough Antimicrobial Coatings Passes Primary Independent Test,” May 31, 2020. https://www.globenewswire.com/news-release/
2020/05/31/2041237/0/en/GrapheneCA-s-Breakthrough-Antimicrobial-Coatings-Passes-Primary-Independent-Test.html (accessed September 10, 2020).
- Lasley, S. “Anti-bacterial coating being developed with miracle material Metal Tech News Weekly Edition,” Metal Tech News, June 27, 2020. https://www.metaltechnews.com/story/2020/03/25/tech-metals/graphene-paint-could-slow-virus-spread/187.html (accessed September 10, 2020).
CoatingsTech | Vol. 17, No. 10 | October 2020