The performance of any antimicrobial additive is dependent on a number of factors… the material being ‘treated’, the target organisms, type & concentration of active substance, test method and environmental conditions all play a significant part.
Provided an appropriate additive is used it is possible to provide excellent levels of performance compared with an untreated material, but it is essential that the efficacy is verified through diligent testing prior to making antimicrobial claims.
It is also important to note some considerations, often overlooked, which can significantly impact the properties of the treated material, both in terms of the antimicrobial performance and the potential compromise of vital material characteristics. These are discussed in more detail below…
The incorporation of any additive into a polymer will have an effect on its physical properties. In many instances, the effect will be indiscernible and in others it will be desirable, either intentionally or as a positive side effect of the main reason for inclusion. However, in some cases the impact can be negative, ranging from mildly inconvenient such as a slight but rectifiable colour shift, to catastrophic such complete loss of flame retardancy.
As part of our standard qualification process, we will ensure that your specific material requirements are understood and addressed, so you can be confident that our additives will not compromise the essential properties of your material.
All antimicrobial testing is carried out by independent laboratories, mostly in the UK.
We employ a variety of test methods, dependent on the material being tested, the end application and the organisms against which efficacy needs to be determined…
ISO 22196:2011… Antibacterial activity of non-porous surfaces. Probably the most widely used method for evaluating antibacterial activity of injection moulded or extruded polymers, cast resins or permanent coatings. Some laboratories also offer the JIS Z 2801 method on which the ISO 22196 was based, but we have moved almost entirely to the ISO method.
The most frequently tested organisms are Staphylococcus aureus and E. coli, although we often test against other bacteria including strains of Salmonella, Pseudomonas, Listeria, Streptococcus and Legionella.
ISO 21702:2019… Anti-viral activity of non-porous surfaces. This was a relatively uncommon test until the COVID-19 (SARS-CoV-2) epidemic but is now, understandably, in very high demand.
SARS-CoV-2 testing is only available from a very limited number of laboratories and is notably more expensive than for most viruses. For this reason, the majority of laboratories offer testing against ‘surrogate’ viruses which are sufficiently similar that one can infer comparable performance against SARS-CoV-2. The viruses most commonly used include Influenza A, Feline coronavirus (FCoV) and Human coronavirus (HCoV NL63). Our preference is generally to test against HCoV, since this is the most logical equivalent and the most meaningful from a consumer perception perspective. That being said, our test evidence suggests that it is more difficult to achieve good performance against HCoV than FCoV.
ASTM G21… Anti-mould activity. While it is feasible to use the ISO22196 or JIS Z 2801 methods for evaluating anti-fungal or anti-mould performance, it is more common to use the G21 test. This is a much longer test, typically carried out over a period of four weeks, with mould/fungal growth evaluated weekly.
We thrive on challenges and are proud of our reputation as a company that can succeed where others have failed. Whether you have a new application or need help with an existing product, we would be delighted to hear from you.