Antimicrobial plastics have been used for many years in moulded fridge linings. The potential benefits would appear to make the additional cost worthwhile, but there are a number of important considerations.
A refrigerator would reasonably be expected to remain in service for perhaps ten years. Silver based antimicrobial additives, such as silver phosphate glass or silver zinc zeolite, would certainly provide adequate longevity, whereas organic antimicrobial alternatives are unlikely to remain active for that length of time. However, the temperature in a refrigerator is notably lower than that at which silver additives tend to be most effective. At the typical refrigeration temperature of 5°C bacteria are not particularly active and silver is most effective when bacteria are undergoing mitosis/cell division, so the efficacy of silver is significantly reduced.
It is worth noting that most silver efficacy data is drawn from standard ISO 22196 tests, which are conducted at 35°C, significantly higher than refrigeration temperature. Antimicrobial plastics which perform well at 35°C will not necessarily perform well at low temperatures…. the only way to be sure is to use a modified test protocol, testing at whatever temperature is relevant to the specific application.
In order to maximise low temperature performance, the choice of antimicrobial plastic becomes more important. Among materials typically used in fridge linings, ABS is probably the most common. Unfortunately, ABS can be quite problematic when used with silver antimicrobial additives, with some grades of ABS performing notably worse than others at a given concentration of antimicrobial. At normal usage temperatures the performance is generally improved by simply increasing the concentration of antimicrobial, but at refrigeration temperatures the loss of perfomance can be too great to overcome economically. The best option is generally to switch to a different grade of ABS.
With careful selection of both antimicrobial additive and polymer, it is certainly feasible to create an antimicrobial plastic that can perform well against bacteria at refrigeration temperatures. Of course, another consideration is the effect of antimicrobial additives on the physical properties of the plastic into which they are incorporated…. but that will be the subject of another post!
