Keeping it clean

The use of anti-microbials in plastics and other substrates in order to keep microbe populations low on surfaces and objects has been a growing area of interest for a number of years. Anti-microbials were originally designed to protect polymers from actual biological attack because in some materials, such as PVC and polyurethane formulations, ingredients in the formulation can act as a food source for the micro-organisms and thus promote growth. The impact of such attack is well documented and can lead to significant effects on a product's properties, including staining, odour formation and the deterioration of mechanical properties. Nowadays anti-microbials are being looked at for use in a wide range of polymeric materials, which are not inherently prone to microbial attack, such as polyolefins, polyester and PC/ABS. In these cases the objective of using the anti-microbial is to inhibit the growth of micro-organisms on the material's surface and thereby reduce the risk of cross contamination, as well as preventing unsightly growth and odour generation.

Bacterial breeding grounds The surfaces all around us can act as transmission sites for potentially harmful bacteria. Various studies have found significant numbers of bacteria on a wide range of items from kitchen taps, refrigerator handles, door handles, telephone receivers to computer keyboards. Not only can commonly touched items act as transfer sites but surfaces that are abraded or scratched can provide nooks and crannies where bacteria can multiply and are difficult to wash off. Contact with contaminated objects such as these can lead to the micro-organisms either being spread to other surfaces or directly to a susceptible individual's face and lips, potentially leading to infection.

Reducing the risks To reduce the risk of infection, regular hand washing and disinfection of areas is critical. However making plastic objects inherently anti-microbial can suppress microbe populations between clean downs and thereby provide an additional weapon against micro-organisms, helping to reduce the risk of cross contamination and provide extra peace of mind. Not only can anti-microbials help prevent cross contamination they can also reduce odours produced by bacterial activity and unsightly discolouration or staining caused by fungi. Anti-microbials are one component of good hygiene practice and must always be used together with a regular cleaning and disinfecting regime. There are several types of anti-microbial products on the market, including both organic and inorganic systems. As a manufacturer of polymer-specific masterbatch, PolyOne offers a comprehensive range of both organic and inorganic systems anti-microbial masterbatch, for use in the full spectrum of thermoplastic materials. The organic systems are based upon small, mobile molecules that once compounded into the plastic are able to migrate between the polymer chains to the surface. Once at the surface the molecules interact with the microbes inhibiting growth. An equilibrium is set up between the reservoir of the anti-microbial additive in the body of the plastic and that at the surface, with further anti-microbial only migrating to the surface when it is wiped or washed. Such systems provide cost-effective solutions, with good antibacterial efficacy and timely protection. Generally they are used in polyolefin applications as they have limited temperature stability. The other type of anti-microbial product available from PolyOne is the silver ion releasing systems. These are based upon particles that contain the silver ions, stabilised to remain unreactive until released by the action of another agent, most typically water. These additives can be compounded into the plastic rather like a pigment or filler. When in the presence of moisture, those particles that are close to the surface slowly release silver ions which are able to inhibit the growth of micro-organisms. With these systems the metal ions remain stored in the polymer, being released only gradually at the surface, providing continual and long lasting anti-microbial activity. The stabilising system used also protects the ions during processing and product storage, helping to prevent discolouration. The efficacy of silver ions as an anti-microbial agent is well known and they find a wide range of medical uses, particularly in the care of burns and wounds. In plastic products silver systems offer the advantage of high heat stability, being stable at temperatures of 500°C and above, making these products suitable for use in both commodity and engineering polymers. Silver is effective against a wide range of bacteria and fungi, and has also been found to slow down the formation of biofilms.

Anti-microbials add value The use of anti-microbial systems in plastic products is a rapidly developing area, with products generating considerable interest and offering manufacturers the opportunity to add value to their products. In the healthcare and food processing industries the use of anti-microbial products offers both manufacturers and consumers real benefits by potentially reducing the risk of cross contamination and the instances of transmission/infection. As there are a number of systems available that can be used in plastics, which exhibit a range of properties, careful choice of the system most suited to the product and process is crucial. PolyOne can help advise customers on the best system for their applications and provide support regarding which test methods to use and how to interpret the results data.