​Framed: Nanoparticles in Paints

The paint industry has also taken full advantage of nanotechnology and has incorporated it to build more efficient, durable, anti-corrosive, adhesive, and super flexible paints. With the help of nanomaterials, the paints with anticorrosive, insect’s killer, self-cleaning effects have come into existence. Therefore, this article aims to discuss such paints and their role in detail.

Background

The anticorrosive protection by means of organic coatings (anticorrosive paints) acts by different mechanisms: slaughter effect (Zn-rich paints), barrier effect and inhibitory effect. Zinc oxide (ZnO) is a conventional white pigment to which different properties are attributed, such as its ability to absorb UV radiation (protecting the resin) and its mechanisms of cathodic and passivating inhibition. It is also used together with conventional active inhibitor pigments such as zinc chromate or calcium borosilicate, increasing the crosslinking density and hardness of paint films.

On the other hand, pigments of conventional size for paints can generate problems such as poor adhesion, reduced flexibility, reduction of impact, abrasion or scratch resistance, and premature delamination. To overcome such inconveniences and improve their behavior, the use of nano pigments has become a recent practice. Due to its inherently small size and particle morphology, many of the problems mentioned above can be overcome.

Nanoparticles in Protective Coatings

The most commonly used nanoparticles in protective coatings are SiO ₂, TiO₂, ZnO, Al ₂O₃, Fe₂O₃, CaCO₃, etc. ZnO nanoparticles are incorporated into water-based alkyd paints at different load levels. The researchers evaluated the anticorrosive behavior of alkyd systems applied to steel and tested the accelerated corrosion in the humidity chamber, salt fog and exposure to UV radiation. They also evaluated the effect of nanoparticles on the physical properties of the paint film (hardness, flexibility, adhesion, and impact) and found that an extremely small concentration of ZnO nanoparticles can improve the corrosion, scratch and abrasion resistance of the paint film. It should be noted that commercially obtained ZnO nanoparticles (<50 nm) were used in this study. A parallel study by the same research group with Fe ₂O₃ nanoparticles reported similar results.

Effect of ZnO Nanoparticles in Paints

The effect of ZnO nanoparticles on the anticorrosive protection of other generic types of paints, other than alkyd systems, has recently been studied including the effect of different charges (2; 3.5; 5 and 6.5%) of ZnO nanoparticles on the corrosion protection provided by an epoxy-polyamide paint film. Steel specimens protected with the epoxy system were immersed in 3.5% by weight NaCl solution, for 1344h. The anticorrosive behavior was monitored by applying electrochemical impedance spectroscopy (HEI). The results indicated that despite the reduction of the cross-linking of the epoxy system due to the presence of the ZnO nanoparticles, the anticorrosive properties of the epoxy film was considerably improved.

This was attributed to two reasons. First, the size of the ZnO particles improves the protection by barrier effect against the diffusion of the aggressive agents towards the substrate. The second reason is hydrophobicity. A similar study was conducted in water-based polyurethane paints. ZnO nanoparticles, commercially obtained and incorporated at 3% by weight in the polyurethane coating, improved corrosion resistance by 2 orders of magnitude under immersion conditions in 3.5% NaCl when evaluated by EIS. The incorporation of ZnO nanoparticles in a coating based on acrylic and silicone resins has also been studied, in which its prominent barrier effect and superior anticorrosive ability were proven.

However, the beneficial effect of ZnO can be improved by modification with other oxides, such as cobalt oxide. This is done by preparing a mixed oxide of Zn and Co, Zn 0.9 Co 0.10, by a ceramic synthesis procedure and another solution by combustion synthesis method (SCS). The pigments, characterized by XRD and FTIR, are incorporated into an alkyd coating in a percentage of 2% using mechanical agitation followed by ultrasonification. The alkyd systems are applied on steel substrates, and evaluated under immersion conditions in 3.5% NaCl by electrochemical polarization and electrochemical impedance techniques. The combination of cobalt and zinc oxides improves the anticorrosive properties of the pigment. The method of preparing ZnO-CoO pigments can influence the characteristics of the particles obtained such as particle size and shape. So,

The green oxides obtained are considered interesting because they are more environmentally friendly than chromium-based pigments. The USEPA (United States Environmental Protection Agency) has developed a list of air pollutants including cobalt and chrome, where the lowest danger of cobalt is clear according to inhalation exposure data.

A study was conducted in alkyd systems to test various ratios of oxides in the ZnO-CoO pigment (5, 10, 15 and 20% CoO) prepared by ceramic procedures. Accelerated corrosion and electrochemical impedance tests revealed that the presence of cobalt improves the action of zinc oxide in a mutual interaction that leads to better corrosion inhibition of the steel substrate.

So, on the one hand, there is a growing interest in assessing the effect of ZnO nanoparticles on the anticorrosive properties of different types of paints (alkyd, epoxy, polyurethane). On the other hand, a beneficial effect of cobalt (CoO) has been found by modifying ZnO when the nanometric mixed oxide is made using SCS. The SCS is a versatile, simple and fast process that allows the effective elaboration of a variety of single or multi-component nanomaterials with pre-designed morphology.

After studying the use of different nano pigments, let’s study the use of nanotechnology in producing insect repellent paints.

Read More about Zinc Oxide Powders, Zinc Oxide Sputtering Targets and Applications, Zinc Oxide Co2 Sensors.

Insects Repellent Paints

Nanoparticles with loads of essential oils, applied to polymer-based paints, could provide an efficient solution as an insect repellent. Infectious diseases due to insect bites are one of the leading causes of death in the world. Statistics mention that mosquitoes are the cause of severe infections, which affect 700 million people a year in the world.

Insect repellents are usually synthetic substances or biopesticides applied directly to the skin, even to the environment in which we are at that time, unfortunately, we inhale them and contaminate our body; Although this contamination is minimal, the problem is presented by the constancy of the application to obtain better results.

Recently, products called “natural repellents” have been released, which consist of electrical devices that, with ultrasonic waves, move insects away from the area where the device is placed and although the marketing calls for its effectiveness, there are still some doubts about it. In general, the means used today as insect repellents have not been as efficient as we would like, due to the short duration of the product on the skin and the environment, as well as the poor quality of electronic devices.

In a project by the Center for Research in Applied Chemistry(CIQA) , it is sought to give added value to common paints for residential or industrial use, so that they function as insect repellents, by incorporating polymeric nanoparticles loaded with essential oils. This is intended to reduce the use of synthetic chemicals that harm our environment more, as well as our bodies. In this way, the direct application of harmful chemicals to the skin as well as their inhalation would be avoided.

The nanoparticles obtained, with an average diameter between 16 and 24 nm determined by the technique of quasi-elastic light scattering (QLS could be incorporated directly into the paint or coating so that once it is dry, it starts to release the essence and thus perform its repellency function.

Nanoparticles Loaded with Essential Oils

The use of essential oils has grown enormously today, as they are used to treat diseases and many of them are used as insect repellents. The weak point of these essences is their high volatility, so the duration in the environment is a few hours. Thus, it was proposed to develop a methodology to synthesize nanoparticles loaded with essential oils to delay the release of the essence, which would lead to an increase in effectiveness in repellency as well as in the duration of the effect and without generating pollution to the environment and the living beings.

The incorporation of microcapsules loaded with essential oils and even synthetic insecticides is a technology that is beginning to spread throughout the world. In Spain, for example, paints loaded with polymer microcapsules that release an insecticide are being used progressively. The expected advantages of nanoparticles developed at CIQA are based on their size much smaller than that of commercial ones. These advantages include a better distribution of the particles in the substrate, as well as a stronger interaction between the component material and the nanostructures.

Self-cleaning Paints

Yao Lu, Ivan Parking and Claire Carmart are three of the researchers from University College London, of the UCL Chemistry department, who in recent years have investigated a new nanomaterial applicable to the field of construction, a self-cleaning paint.

The nanomaterials are part of the near future of construction, where they are expected to be able to provide significant advantages in terms of improved strength and other properties, including the self-cleaning capacity of the materials. The study entitled Markets for Self-Cleaning Coatings and Surfaces: 2015 to 2022 , establishes that the market for self-cleaning materials will grow about 3.3 billion dollars before the next three years.

Lotus Effect

The self-cleaning paint created by the UCL is a composite coating based on coated titanium dioxide nanoparticles, used for its non-toxicity and its stability in moisture-resistant aqueous solution. The finish rejects water and other liquids such as oil, creating a pearly effect on the surface. The water applied on the surface finished with this product forms drops of various sizes that slide over the material, dragging in its path the dirt deposited on the surface, which is mixed with the water, favoring self-cleaning. The process, discovered in 1973 by the botanist Wilhelm Barthlott, is known as the "Lotus Effect", for mimicking the natural washing that occurs on the surface of its leaves and other aquatic plant species.

For this effect to take place the surface must be rough and waxy. The challenge of the research was to create these conditions on hard and soft surfaces, designing a paint that, combined with different adhesives, was able to maintain water repellent properties after the surfaces were damaged.

Different coating methods were used for the different surfaces tested depending on the material: glass, steel, paper, and other materials. The paint responded well for all of them, in which the wear of these materials during their useful life was simulated. The tests were performed on samples with an area of 20 cm ², but it is demonstrated that the product can work in large areas such as those of the exterior or interior walls of a building. One of the main advantages of the product is that during the self-cleaning process, not only the dirt is dragged, but also the viruses and/or bacteria present on the surface, which determines the suitability of its use in interior linings of buildings.

Conclusion

So, this is only the tip of the iceberg. Multiple possibilities of materials are appearing every day. We leave out of discussion aspects such as innovative design possibilities, composite materials with high structural properties that allow new architectural solutions, mortars, fast-setting concrete, which reduce process times, with superior mechanical properties. A whole new world, a real revolution with great expectations for the future has just begun.

Check our article on Nanomaterials in Construction.

References

https://www.prnewswire.com/news-releases/markets-for-self-cleaning-coatings-and-surfaces-2015-to-2022-300254735.html

https://discovery.ucl.ac.uk/id/eprint/1546191/1/Lu_Yao_Thesis-Yao%20Lu.pdf

https://www.sciencedirect.com/science/article/pii/S2352573815300020

https://www.researchgate.net/publication/228524310_Synthesis_of_Wurtzite_Nano-crystalline_ZnO-CoO_Pigment_by_High_Energy_Milling

https://www.sciencedirect.com/science/article/pii/S030094401930325X

https://www.researchgate.net/publication/327193611_What_factors_affect_lotus_effect