Doped elastomers prevent the growth of bacteria, fungi, and yeasts on rubber parts, while avoiding challenges that organic biocides have posed in the past
The speciality elastomers business of Milliken Chemical has announced the introduction of a new line of antimicrobial heat-cured rubber compounds that can help solve cleaning challenges in food-processing, medical, industrial, and other applications prone to microbial growth.
Called Elastoguard, these patented antimicrobial elastomers provide an effective way to prevent the growth of bacteria, fungi, and yeasts on rubber parts, while avoiding challenges that organic biocides have posed in the past.
Rubber parts can be particularly vulnerable to attack by bacteria and fungi because their chemical constituents provide an ideal source of nutrients that support microbial growth.
Furthermore, rubber parts are often used in warm, moist environments rich in microorganisms - conditions that are ideal for proliferation of these life forms.
This, in turn, can lead to costly cleaning challenges requiring significant equipment downtime and disassembly and premature deterioration of elastomeric components.
To reduce or inhibit microbial growth both within and on the surface of rubber parts, compounders have traditionally blended antimicrobial (AM) additives into elastomers.
However, the chemicals used have tended to leach out of the matrix material, so not all areas of a part are protected, and the microbe-suppressing properties diminish over time as the additive migrates away.
These chemicals also tend to degrade at elastomeric processing temperatures exceeding 250C, causing them to volatilise and corrode the rubber-moulding equipment.
Additionally, the presence of such chemicals can contribute an unpleasant taste or odour to the elastomer.
Finally, there are growing concerns about the safety of many commonly used organic biocides.
In response to this problem, Milliken has developed the Elastoguard family of antimicrobial rubber compounds.
These elastomers have demonstrated excellent control of microbial growth - both incremental and long-term, and on the surface as well as inside the treated material - even after repeated surface abrasion and washing.
In fact, performance is enhanced over time by usage and by other actions that occasionally scuff up the surface of the part, exposing more of the silver-based antimicrobial agent used in the new materials.
The new and patented biocide used in Elastoguard compounds - Antimicrobial Alphasan silver-sodium-zirconium-phosphate (silver-NZP) ion-exchange resin - permeates the entire rubber part, so it provides skin-to-core protection without the zones of inhibition and non-inhibition common with organic biocides.
The silver-based AM agent is non-leaching, so parts achieve much more thorough and long-term protection than is offered by organic biocides.
It is also extremely heat stable (>800C) and works by slowly releasing silver ions (Ag+), which are exchanged for other common, positively charged ions readily available in the surrounding environment.
Scientists theorise that the silver is absorbed by the microbes (along with other essential ions), where it begins to interrupt formation of vital enzymes used in energy production, causing the microorganism to quickly lose its ability to grow and reproduce.
Unlike antibiotics and certain organic biocides, silver's mechanism of action against microbes is very non-specific, making it extremely difficult and rare for microorganisms to develop resistance.
While highly effective as a biocide, silver-NZP is considered safe, non-irritating, non-toxic, and requires no special handling.
Once vulcanised, the silver antimicrobial is encapsulated in the rubber matrix.
It has attained numerous regulatory registrations around the world for contact with food and potable water and for use in medical devices.
Silver itself has a long history of use as a biocide and today is used in numerous medical treatments.
It has been used for millennia for eating utensils, cups, jewelry, and other decorative and functional devices that are safe for human contact.
The silver biocide is odourless, extremely insoluble, and neither flammable, explosive, nor corrosive.
It does not impart an additional taste or smell to rubber and does not affect the colour stability of the moulded part, so it can be used in white or light-coloured compounds.
Furthermore, the silver-based biocide is not sensitive to heat or shear, so it can be used in elastomers formulated for a variety of processes without concern.
Finally, this technology provides both antifungal as well as antibacterial properties to finished parts - a versatility that is rarely found among traditional antibacterial compounds.
Elastoguard antimicrobial heat-cured rubber compounds are now commercially available from Milliken Chemical in standard formulations ranging from natural rubber through workhorse EPDM and NBR grades, to high-performance fluoroelastomers, in Shore A hardness ranges from 40 to 90.
Within these product families, the compounds are offered in a variety of presentations (forms), including slabs, strips, calendared sheet, granulated/pelletised, and preformed into specific shapes.
