Date:Sep 28, 2022
Author:Ian FellowsThe market intention is to develop new products with enhanced properties, a reduced carbon footprint, and extended durability. Graphene nanotubes allow manufacturers to create completely new materials or market products with a full set of required properties. Here, we will explore the specific properties of graphene nanotubes that enable them to enhance different types of industrial coatings.
Graphene nanotubes, also known as single-walled carbon nanotubes, facilitate a unique combination of properties in coatings, including: targeted conductivity, durability, high performance, and aesthetic appearance. Each graphene nanotube is a sheet of graphene rolled into a tube with a wall the thickness of a single atom of carbon, a diameter of about 1.2–2 nanometers, and a length of around 5 microns. This material has an extremely high aspect ratio – the ratio of length to diameter – which results in graphene nanotubes’ unique morphology and performance.
Graphene nanotubes are one of the strongest materials on Earth with a similar conductivity to copper. They are very flexible in contrast to stiff multi-walled carbon nanotubes. When evenly dispersed, they can achieve targeted conductivity and can even improve mechanical properties even at dosages hundreds of times lower than that of other conductive additives.
In contrast to standard anti-static additives, graphene nanotubes guarantee stable and uniform conductivity, leading to increased safety. Their ultra-low working dosages open the door for light-colored lining coatings, resulting in quicker and easier routine inspections. 4-12 wt.% of carbon black can be substituted with just 0.03 wt.% of graphene nanotubes in various epoxy coatings. This tiny amount is enough to provide stable and permanent surface resistance of 104–108 Ohm/sq and preserve high bond strength and adhesion, and high resistance to wear, abrasion, and impact, making it possible to avoid time consuming and costly remedial maintenance.
A wide range of available colors speeds up visual inspections and facilitates more efficient servicing. It allows a servicing company to apply a black layer and then a light one, and in the areas where there is a contrast between these two layers, it can be easily recognized as not having an appropriate thickness of the layers. Additionally, during operation, it will be much easier to inspect defects on the internal surface of the lining if it is light in color.
The new anti-static lining with graphene nanotubes is used in storage tanks for crude oil, fuel oil, diesel oil, jet fuel, motor gasoline, and similar liquids. As well as tank linings, it can be used for tankers and containers in transportation, chemical processing, electronics manufacturing, pharmaceuticals, and other applications. Graphene nanotubes provide permanent properties that don’t depend on environmental conditions such as humidity. Enabled by nanotubes, permanent electrical conductivity remains for the life of the tank lining coating.
The next application where replacement of standard additives with graphene nanotubes brings noticeable added value is self-leveling floors. The addition of graphene nanotubes makes it possible to grant stable, homogeneous anti-static properties to floors, while maintaining the key strong points of original epoxy floors, such as good durability, abrasion resistance, and a wide color palette.
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An ESD-compliant floor top coating for static-sensitive areas has been developed by adding just 0.01-0.04 wt.% of graphene nanotubes. It demonstrates permanent, homogeneous resistivity to ground and surface-to-surface resistivity of 104–1011 Ohm without hot spots or black dots, regardless of humidity. Graphene nanotubes provide unmatched performance in comparison with standard anti-static additives. They make it possible to maintain the mechanical abrasion, impact and chemical resistance, water and dust repellence of the host material.
An ultra-low dosage of graphene nanotubes can replace up to 4% of chopped carbon fibers or 30% mica without significantly changing the basic formulation of a flooring compound or incurring additional expenses. The low working dosage of nanotubes protects color pigments from being overwhelmed by the usually high loading of anti-static additives required, avoiding dark shades in the final coating.
Because of the length of chopped carbon fiber (2 mm or longer), the thickness of the base layer must be at least as much (~2 mm). This can result in difficulties in the installation process, increased costs, and the possibility of there being insulating “hot spots”. In contrast, graphene nanotubes can be used with various anti-static flooring systems and thicknesses, and provide easy-to-pass walking tests.
The modified floor meets the highest demands where the system shoe – floor provides the primary grounding complying with ASTM F150 (106 < R ≤ 109 Ω), EN61340-4-1, ANSI/ESD S7.1 (RG < 109 Ω) standards. Typical applications include industries that process, assemble, install, package, test, or transport, such as the cleanroom, pharmaceutical, and automotive industries.
Graphene nanotubes added into acrylic automotive primers with a very low surface resistance and high adhesion make it possible to apply base coats and other coating systems to automotive exterior plastic parts via a cost-effective method: electrostatic application. This is possible because conductive acrylic primers for polypropylene parts with graphene nanotubes demonstrate a stable, uniform level of surface resistivity of around 105 Ω/sq.
Primers with L-Value between 67 and 75% can be produced with the required concentration of nanotubes starting from 0.01 wt.%. This becomes apparent when the same thickness of the base coat is applied over dark gray carbon-black based primers and light gray graphene nanotube-based primers. The L-Value of a nanotube-based sample is much higher. As a result, the consumption of base coat can be decreased, reducing the costs for the whole formulation.
Today, it is possible to create a conductive primer not only for PP bumpers but also for SMC exterior parts. Initial trials have shown that it might even be possible to assemble SMC parts coated with primer and a metal body then let it go through a cataphoresis process (e-coating), then oven drying, and finally to apply a base coat via an electrostatic method. Such painting of exterior parts directly on the conveyor is a huge advantage for OEM producers.
Powder coatings with good surface quality and a simpler application process are possible with graphene nanotubes. The new product is anti-static powder paint. Graphene nanotubes provide permanent, stable, homogeneous surface resistivity ranging from 103 Ω/sq to 109 Ω/sq without insulative spots or any dependence on humidity. Finished products show positive results in combining the targeted conductivity with aesthetic performance in a variety of surface textures and colors.
Traditionally formulated high conductivity powder systems rely on conductive carbon black, which limits pigmentation options. By switching to a graphene nanotube system requiring drastically lower dosages, a significantly wider range of color options are available.
Compatible with most engineering plastics and metal substrates, sprayable electrically conductive powder coatings with graphene nanotubes are highly welcomed in electrostatic-sensitive applications in ATEX hazardous environments and the instrumentation, medical, marine, aviation, and defense industries.
The low working dosage of nanotubes makes it possible to do more with less: less raw material is required to create higher-performance products. Coating sustainability is facilitated by nanotubes extending the durability of the coating, increasing production cost-efficiency, and reducing the environmental impact. Using sustainable solutions based on graphene nanotubes contributes to reaching the global Net Zero target – the overall effect of graphene nanotubes on emission reductions is 6,300 mlt tonnes of CO2-eq by 2050.
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Read the original text:
Exploring the ability of graphene nanotubes to enhance coating safety, durability, and performance. PCI mag (September 2022): https://digitaledition.pcimag.com/september-2022/feature-ocsial/