The word antimicrobial was derived from the Greek words anti (against), mikros (little) and bios (life) and refers to all agents that act against microbial organisms. Antimicrobial products kill or slow the spread of microorganisms. Microorganisms include bacteria, viruses, protozoans, and fungi such as mold and mildew.
Antimicrobials are used across many applications and consist of very diverse chemistries. In water treatment, some microbes are necessary, whereas an overabundance can overwhelm a water treatment facility. Antimicrobials are used in wood preservation; for the protection of textiles and non-wovens used in manufacture of tents; and in sporting equipment and outdoor furniture to prevent mold and mildew. They are used widely in crop protection to avoid rot and mold; molluscicides (used to control garden snails); and for preserving waterborne metalworking fluids used to lubricate cutting edges for milling steel and other metals. In personal care, they are found in hand sanitizers, wound cleansers, dressings, etc.
Antimicrobials (A-M) consist of numerous organic chemistries, as well as inorganics. Zinc oxide has been a key ingredient for mildew protection in coatings for years. Copper is utilized in ACQ (aqueous copper quat treatment for pressure-treated lumber which replaced arsenic-containing CCA), and had been used in now-banned ship bottom paints. Copper can be overly effective, and was discontinued for below waterline applications due to high toxicity to more-than-targeted organisms. It has been replaced by various highly-effective inorganic antimicrobials and by addressing fouling using a surface modification approach.
An organotin called tributyltin oxide (TBTO) had also been used as a marine anti-biofouling agent, but concerns over toxicity of these compounds have led to a worldwide ban by the International Maritime Organization. Fortunately, banned substances have been substituted by effective, but relatively innocuous materials. More recently, nanosilver and other metals have been found to be effective in the reduction of human odor-causing bacteria, and are incorporated into fabrics.
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The U.S. Environmental Protection Agency (EPA) regulates antimicrobial products as pesticides, and the U.S. Food and Drug Administration (FDA) regulates antimicrobial products as drugs/antiseptics. As pesticides, antimicrobial products are used on objects such as countertops, toys, grocery carts, and hospital equipment. As antiseptics, antimicrobial products are used to treat or prevent diseases in people, pets, and other living things.
If a product label claims to kill, control, repel, mitigate or reduce a pest, it is a pesticide regulated by the U.S. EPA. When manufacturers make this kind of claim on the label, they must also include:
- application instructions that are effective at killing or controlling the pest, and
- first aid instructions, in case of accidental exposure.
Specific to coatings, surfaces where an antimicrobial could be used include: walls and floors in hospitals and other institutions, such as schools; exterior surfaces prone to mold, algae and mildew; ship bottoms (antifouling coatings); and public surfaces such as handrails, light switches, etc. Many of the antimicrobial materials used in coatings can also be employed in composites and plastics.
Due to the lengthy regulatory approval process for new antimicrobial materials, fewer and fewer products are launched every year. A review of the most recent patent applications for antimicrobials shows 7 citations. Most of the A-M patent filings, are application-related and methodologies using existing chemistries.
Antimicrobials do have specific pH ranges in which they are most efficacious. Using a biocide effective in pH 4-10 in a polyvinylidene chloride resin (such as DSM Haloflex 202S) would be a poor choice, since the resin’s pH is 1-2. Some companies have combined approved products to create blends of non-reactive materials, thus avoiding the full registration process and extending the effectiveness over a greater pH range or against additional microbes.
Microbiocidal materials used in paints kill micro organisms on the surface of the coating. In the March 2016 issue of D+D In-depth, Sherwin-Williams is presented as having introduced the first EPA-registered microbicidal paint, called Paint Shield. It kills greater than 99.9 percent of Staph (Staphylococcus aureus), MRSA (Methicillin-resistant Staphylococcus aureus), E. coli (Escherichia coli), VRE (Vancomycin-resistant Enterococcus faecalis) and Enterobacter aerogenes within two hours of exposure on a painted surface, based on results from a third-party, EPA-inspected, Good Laboratory Practice (GLP) lab. In the same issue, other articles address the use of coatings for the improving quality of health.
Mildew will grow on any untreated surface, as will many types of algae and mold, if they have the correct nutrients to exist and water. Due to global regulatory changes, some previously-approved mildewcides, as well as other antimicrobials, have been banned from use. This has caused the industry to scramble for replacements.
The use of active and passive microbiocidals in paint has brought hope that hospital infectious diseases can be reduced further through their use.
 Title 40, Part 152 - Pesticide Registration and Classification Procedures, Protection of the Environment; Code of Federal Regulations. http://www.access.gpo.gov/nara/cfr/waisidx_10/40cfr152_10.html
 D+D In-depth, “Paint as a Powerful Tool in Health-Care Settings” Steve Revnew, March 2016; http://www.durabilityanddesign.com/archive/
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