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As construction and industry grow, it is expected that the application of antimicrobial, antifungal and antibacterial biocides will continue to rise as well. Biocides in paint allow for the prevention of the unwanted growth of fungus, algae and bacteria that can be extremely destructive to painted surfaces.
While adequate biocides are currently used in the market today, researchers expect that the future application of nanomaterial biocides into paints may have superior antimicrobial properties at a reduced cost.
Microorganisms and Paint
The deterioration of both exterior and interior paints often occurs as a result of exposure to microorganisms. These microorganisms are typically fungal species that are attracted to moisture, such as external environments of high temperatures and humidity levels, as well as interior locations, such as the kitchen or bathroom, where such conditions are accommodating for this type of microbial growth.
When microorganisms attack paint, the paint surface is covered with a network of cells that can sometimes discolor the paint through their spore production, or by allowing for increased dirt retention1. Subsequent discoloration and disfigurement of the painted surface will also occur.
Traditional Paint Biocides
Some of the earliest biocides that were originally integrated into paints contained highly toxic heavy metal ingredients such as phenyl mercuric acetate (PMA) and tributyl tin (TBT)1. The ability of these metals to severely damage the environment combined with their limited effectiveness as antimicrobial additives caused for their ultimate replacement in the market. The following table describes current biocides that are used in the paint industry based on their specific targeted biological organism2.
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Classification of Biocide
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Examples
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Fungicide
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- Carbendazim (BCM)
- Chlorothalonil (CTL)
- Iodopropynylbutylcarbamate (IPBC)
- Octylisothiazolinone (OIT)
- Dichlorooctylisothiazolinone (DCOIT)
- n-butyl-benzisothiazolinone (BBIT)
- Zinc Pyrithione (ZnPT)
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Algaecide
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- 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron)
- 2-(tert-butylamino)-4-(cyclopropylamino)-6-(methylthio)-1,3,5-triazine (IrgarolTM)
- 2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine (terbutryn)
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The aforementioned biocides that are currently incorporated into paint products exhibit a high specificity to the targeted organism, however these products are often very costly and lack the overall performance of the traditional metallic biocides.
Nanomaterial Biocides in Paint
The outstanding properties of nanoparticles have enhanced the way in which a number of industries around the world operate. With regards to the paint and coatings industry, researchers believe that nanoparticles can improve the hardening, UV-light absorption and biocide properties tremendously. Currently, titanium dioxide (TiO2) and silicon dioxide are the most relevant nanomaterials used in paints, however further investigation on the potential of silver, zinc oxide, aluminum oxide, cerium dioxide, copper oxide and magnesium oxide must still be conducted.
Nanosilver
The high antimicrobial properties of both silver ions and nanosilver is attributed to the ability of this material to bind to bacteria cell proteins to induce cell death. Previous uses of nanosilver paint products have shown that the overall antimicrobial, deodorizing and protection of paint surfaces from mildew and various bacteria strains is superior to current biocides. Additionally, nanosilver also showed to be far less toxic to the environment as compared to other popular paint biocides.
Nanotitantium Dioxide
When combined with sunlight or UV light, TiO2 nanoparticles are well known nanomaterials for their photocatalytic activity that produces hydroxyl radicals in water to ultimately attack organic compounds, such as cellular proteins in bacterial organisms. This unique activity allows TiO2 nanoparticles to exhibit self-cleaning properties that have already found successful application in indoor paints, however further investigation on these nanoparticles must be conducted so that full oxidation of organic compounds can be achieved.
Nanocopper
As a commonly used component of agricultural pesticides, copper, as well as its nanoparticle form, induces cell death by the generation of reactive oxygen species (ROS), which is highly damaging to most biological molecules including DNA, protein and lipids. Copper toxicity is dependent upon the ratio of organic and/or inorganic copper in solution, however nanocopper is significantly less toxic as compared to its bulk counterpart. Nanocopper exhibits effective antimicrobial activity in concentrations as low as 40-60 mg/mol3.
Moving Forward
Currently, the replacement of engineered nanoparticles for biocides used in paints is still in its early stages, therefore a great deal of research must still be conducted on how the impressive antimicrobial properties of these nanoparticles can prove useful for these industries. Furthermore, researchers are also interested in investigating how these and other nanoparticles can improve the water repellence, scratch resistance and overall durability of paints.
References and Further Reading
- “Handbook of Biocide and Preservative Use” A. Downey, 1995, Springer, Dordrecht.
- “The Development of High-{Performance Paint Film Biocides” – Paint & Coatings Industry
- “Is nanotechnology revolutionizing the paint and lacquer industry? A critical opinion” Kaiser, J., Zuin, S., Wick, P. Science of The Total Environment. (2013). DOI: 10.1016/j.scitotenv.2012.10.009.
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