The integration of engineered nanoparticles in façade coatings may lead to improved or new functionalities during their life cycle. Nanomaterials may improve environmental sustainability by saving materials, substituting hazardous substances and improving the durability of the coating. However, extended applications of nanomaterials raise concerns about potential risks for human health and the environment.
Market drivers
Dirt collection (accumulation) in building exteriors poses considerable problems for building maintenance. Cleaning these building surfaces generally involves using detergents accompanied with scrubbing, wiping and high-pressure water jets. These processes have several shortcomings such as use of chemical detergents, high consumption of energy and labour cost. This naturally leads to high maintenance costs; therefore, an effective self-cleaning or low maintenance coating is desirable.
Performance benefits
Nanocoatings are beneficial for protecting the surface of various construction materials such as glass, concrete, sand limestone or marble from environmental influences such as water staining, moss, algae as well as soot and oil stains; and also function as corrosion inhibitors for reinforced steel.
In recent years, self-cleaning coatings using photocatalytic nanoparticle titanium dioxide (TiO2) have gained considerable industry traction. With the assistance of little UV light from fluorescence source or sunlight, TiO2 offers two unique properties: (a) strong oxidation power, and (b) super-hydrophilicity.
Strong oxidation power can be used to kill bacteria attached on the wall, or oxidize/remove foul smells from stains in toilets (e.g., TiO2-coated tiles and TiO2-coated glass are commercially available products). Super-hydrophilic properties allow dirt and stains to be easily washed away with water or by rainfall when such a coating is applied to exterior surfaces.
Nanoparticle TiO2 self-cleaning coating greatly benefit building maintenance, especially for skyscrapers, as they reduce the need for costly surface cleaning. Photocatalytic nanocoatings are also used to improve indoor air quality by reducing the amount of volatile organic compound (VOCs) and other toxic chemicals people are exposed to in hotels, restaurants, commercial business facilities, university laboratories, hospitals and residences.
Commercial window films can gain competitive advantage by embedding nanoparticles into plastic films later applied to glass surfaces. Nano films offer heat absorption and reflective properties while maintaining fairly high levels of transparency.
Concrete structures also make profit from nano-enhanced coatings that prevent graffiti and other unwanted stains to adhere on to it. Anti-stick properties of nanocoatings leads to less staining and easy-cleaning-effect on exterior and interior surfaces. Anti-graffiti properties mean that stubborn stains such as graffiti, which in the past called for intensive cleaning efforts can be washed away simply with a high pressure hose.
Image: Exterior wall coated with nanocoating.
Commercialization
Dirt repellent protective paints and photocatalytic coatings are the most prominent applications in the construction and exterior protection industry. The Sodra Lanken tunnel in Stockholm has been coated with a nanocoating to prevent dirt accumulation.
As well as widely commercialised nanoTiO2 products, paints and surface coatings incorporating nanomaterials are commercially available that create a low energy facing thus rendering a building surface highly hydro- and oleophobic, thereby helping to prolong maintenance cycles and reduce cleaning.
A number of multinational companies, including Evonik Degussa, Dupont, Schott, 3M and Corning produce anti-fouling and easy-to-clean coatings for a variety of markets. Water-based, VOC-free, clear impregnating nanoparticle wood coatings containing nanoscale UV absorbers have also been commercialised. They are designed for use on masonry and concrete surfaces, provides superior water repellency, reduces efflorescence, and provides significantly improved abrasion resistance. Anti-graffiti nanocoatings have also been developed that are commercially available.
