The power of covalently bonded coatings

Mohamed Shaik Dawood, R&D Manager, Coval Technologies, discusses the advantages of covalently bonded coatings

Main image caption: The chemical, covalent bond of a Coval coating is demonstrated in the lab with adhesion test results. Once the dolly was moved, it tore away the concrete that it had covalently bonded with from the substrate below

In the dynamic landscape of surface coatings, innovation is key to achieving superior performance, durability and reliability. Among the various coating techniques available, covalently bonded coatings stand out as a game-changer, offering unmatched advantages over mechanically bonded alternatives. 

Coatings bond to substrates through various mechanisms, depending on the coating material and the substrate’s properties. The two most common ways that a coating bonds to a surface are mechanically and chemically (covalently). Mechanical bonding occurs when the coating physically interlocks with the substrate surface. This can happen through surface profiling, where the substrate is made porous or textured to create microscopic or macroscopic irregularities. The profiling also allows the coating to soak into the substrate to create solid anchor points for the topical coating. The coating then adheres to these irregularities, forming a mechanical bond. Mechanical bonding is common in coatings such as acrylic, alkyd, epoxy and urethane. 

Mechanically bonded coatings 

Mechanically bonded coatings can fail on smooth surfaces due to inadequate adhesion caused by the lack of surface profile. When a mechanically bonded coating is applied to a smooth surface, there are fewer opportunities for mechanical interlocking or physical adhesion between the coating and the substrate. 

Manufacturers will specify the surface profile in their data sheets using the AMPP Concrete Surface Profile Specification, which rates concrete surface profiles between 1 and 10, with 10 being the most aggressive. Mechanical profiling is a large cost component when installing coatings due to the need for chemicals, grinders, shot or sand blasters, and possibly even concrete scarifies. 

Covalently bonded coatings 

Covalent bonds are complex network reactions which involve the sharing of electrons between atoms, are fundamental in organic and inorganic combined chemistry, and occur naturally in many substances. Diamonds, for example, are carbon atoms arranged in a crystalline structure, where each carbon atom forms four strong covalent bonds with neighboring carbon atoms. 

Nanotechnology is used to precisely engineer the structure and composition of the coating materials, allowing for the formation of strong covalent bonds between the molecules made up of organic and inorganic chemicals and the substrate. By controlling the size, shape and surface chemistry of these nanoparticles, we can optimise their ability to form strong and durable covalent bonds to various substrates. At the core of covalently bonded coatings lies the strength and stability of the chemical bonds formed between the coating material itself and the substrate surface. This exceptional bonding strength, with strong hydrophobic properties, not only enhances the durability of surfaces in rigorous environments but also ensures long-term protection against abrasion and wear due to strong adhesion and chemical resistance. 

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Smooth surfaces 

Smooth surfaces, such as polished concrete, aluminium, steel and some stone, present unique challenges for traditional mechanically bonded coatings. These surfaces lack the surface roughness required for mechanical interlocking, leading to poor adhesion and coating failure. Covalently bonded coatings do not require a surface profile as they form strong chemical bonds with the substrate at the molecular level. 

Peeling and running 

Mechanically bonded coatings rely on physical adhesion to the substrate, which can lead to issues like peeling and running, especially in demanding environments or when exposed to harsh chemicals. These coatings are susceptible to delamination, blistering, and other surface defects over time due to their reliance on mechanical adhesion. 

Covalently bonded coatings, however, form a stronger and more durable bond of adhesion. By forming chemical bonds with the substrate, these coatings create a seamless and impervious barrier. This makes them highly resistant to peeling, running, and other forms of degradation, even in challenging and harsh conditions. 

Surface preparation 

Another significant advantage of covalently bonded coatings is the minimal surface preparation required for application. Unlike mechanically bonded coatings, which often necessitate extensive surface roughening and priming to achieve adequate adhesion, covalently bonded coatings offer greater simplicity and efficiency in the coating process. 

Challenges with covalently bonded coatings 

The biggest issue with covalently bonded coatings is that they can only be applied very thinly, or in thin layers after each layer is cured. The chemical reactions involved in forming covalent bonds are impeded when the coating is applied too thick. Often, thicker coatings may experience issues such as cracking, delamination, or uneven curing due to internal stresses, thermal expansion, or other physical factors. Covalently bonded coatings need to maintain their integrity and adhesion to the substrate, and increasing thickness can exacerbate these challenges. 

Caption: The adhesion test for this Coval coating sample created a deep pit upon removal, stripping away concrete and expressing the strong covalent bond of the coating to the concrete

Covalently bonded coatings are highly reactive 

Covalently bonded coatings are not fully reacted until they are cured. That is, when they are in liquid form, they are only halfway through their reaction process. Once they meet a substrate and, in most cases, are exposed to moisture in the atmosphere, their final reaction occurs. This means that they must be stored properly and are susceptible to any impurities in the reaction process or any contaminants on the substrate. Therefore, surfaces must be cleaned thoroughly to remove any oils, surfactants, or other contaminants. Highly reactive coatings, due to their very nature, also have limited working time for the applicator. 

Future developments 

Covalently bonded coatings have been around for several decades. Advancements in material and technology have seen exponential growth in their performance and usability over the past 10 years. The paint and coatings industries are only at the very beginning of utilising this technology. Companies around the world are actively engaged in a race to further develop a range of covalently bonded products and methods of application. This pursuit is driven by a commitment to delivering enhanced performance, cost-effectiveness, and sustainable solutions through reduced maintenance and business success. 

Conclusion 

Nanotechnology plays a crucial role in covalently bonded coatings by enabling precise control over molecular interactions and structure at the nanoscale. By leveraging nanoscale engineering principles, we can develop coatings specifically designed for their desired purpose. 

Covalently bonded coatings represent a paradigm shift in surface protection technologies, offering unparalleled advantages in terms of bonding strength, preparation simplicity, and resistance to peeling and running. The potential of covalently bonded coatings is boundless. 

As stewards of industry advancement, it falls upon us to embrace innovation, harness the power of covalent chemistry, and drive progress in surface coating applications. The future is bright, and with covalently bonded coatings leading the way, we’re poised to reach new heights of excellence in surface protection and beyond. 

Coval Technologies manufactures a range of covalently bonded coatings for many substrates including concrete, tile, stone, aluminum, rubber, plastics, fiberglass, and metals. Coval is laser focused on developing new covalently bonding sustainable technologies to bring to the market. 

Author: Mohamed Shaik Dawood, Research & Development Manager, Coval Technologies

Mohamed Shaik Dawood has a proven track record in coatings, developing a myriad of coatings products from primers to speciality coatings. As Research and Development Manager of Coval, he is responsible for enhancing existing coatings and sealers while directing the development of innovative products aligned with industry and market demands. Previously head of R&D at PT Propan Raya ICC in Indonesia, he has expertise in both solvent and water-based formulations for application across numerous substrates.