Frequently Asked Questions
Antimicrobials in Plastic Products
Antimicrobial applications can be a confusing subject — when it doesn't have to be. Straight answers to the questions we hear most.
What is the purpose of an antimicrobial?
Plastics are composed of polymers and their enhancing additives, with most being from organic petrochemical or biomass feedstock. Because of this they are susceptible to attack by microorganisms who view the plastic as a source of food. The inclusion of an antimicrobial protects the plastic from degradation by microorganisms. A second benefit is the ability to reduce the number of colony forming units (CFUs) of microorganisms — including those creating perilous environments. The result is a surface that is significantly enhanced to resist the transfer of microorganisms by touch, as well as reducing discoloration and odors.
How do antimicrobials work?
Most antimicrobials are dependent on the targeted microbe to either ingest or absorb the active ingredient directly or by ionic exchange. A hydrophilic environment is necessary to ensure the antimicrobial is readily available — the “leaching” process in which moisture-dependent technologies function. The organosilane antimicrobial has a mode of action based on molecular penetration of the microbe's cellular membrane — a physical softening and then rupture of the cell wall, not dependent on leaching to be available.
Are antimicrobials safe to use?
When we consider an antimicrobial that is EPA registered, we can be assured that the technology has been subject to rigorous scrutiny before its approval for use in the public domain. The EPA registration is very specific in the applications for which the technology is approved. However, understanding the various antimicrobial technologies is a responsibility for all who are incorporating them into plastic products for everyday use.
Are there environmental concerns for using antimicrobials in plastics?
If there are concerns, the three primary areas would most likely include:
- Effects on the work environment from dosing the plastic during the manufacturing process
- Migration of the antimicrobial during the functional life of the resulting treated article
- Decomposition of the antimicrobial at the end of product life
Are there end-of-life issues for antimicrobials?
When the functional life of a plastic product containing antimicrobials is reached, the behavior of the antimicrobial needs to be considered. If the technology is dependent on leaching, does the antimicrobial continue to leach? If and when the plastic decomposes, does the antimicrobial active decompose?
Where is the ROI for using antimicrobials in plastics?
A product designed to be manufactured of plastic remains dependent on the physical properties of the polymer throughout its useful life. Having the advantage of the plastic to include antimicrobials to protect against degradation by microbes is a sound engineering practice and adds value. As well, antimicrobials that are effectively present on a 24/7 basis offer additional protection to the plastic surface itself — enhancing good housekeeping practices for cleanliness and pleasing aesthetics.
How do you measure the effectiveness of an antimicrobial in plastics?
Efficacy is reported in terms of log reduction or percentage reduction of the microorganism colony forming units (CFU) specified within the applicable test protocol.
- Leaching antimicrobials use a 24-hour timeline; JIS Z-2801 or ISO 22196:2007 use a cover-slip technique for 24 hours of contact.
- Non-leaching antimicrobials use ASTM E2149-10 — the treated article is dynamically shaken in the inoculum for one hour.
- ASTM G-21-09 is a common protocol to determine resistance to fungi in polymeric materials.
What is the cost to use antimicrobials in plastics?
The formula to determine the premium cost should start with determining the objective for the antimicrobial. The next step is to determine which is the best-suited antimicrobial and how much is required for the polymer being treated to meet the objective. This can be determined by incorporating a DOE that includes a ladder of antimicrobial concentrations and efficacy testing of the resultant ladder. With this, the premium can be determined as a matter of the necessary antimicrobial and its volume to meet the end-use application objectives.
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