An antimicrobial masterbatch is a mixture of antimicrobial additives that are compounded into a suitable polymer carrier and formed into pellets. This antimicrobial polymer masterbatch is then incorporated into the bulk polymer material by manufacturing processes such as extrusion or injection moulding, to provide long term antimicrobial efficacy, often for the life of the product.
Most moulded or extruded materials will contain additives of some kind, whether pigments, fillers, processing aids or performance enhancers. Many of these additives are powders or liquids which are messy to use and difficult to dose and disperse accurately. A masterbatch is essentially a carrier, typically the same as the bulk material, containing a high concentration of these additives, which is then blended with a standard polymer prior to, or during, the moulding or extrusion process. This removes the need for working with the additives in their natural powder or liquid form, eliminating the associated difficulties and generally ensuring more consistent dosing and better dispersion.
How is an antimicrobial masterbatch made?
Most polymer masterbatches would be manufactured using a twin screw extruder. The additives are either batch blended with the carrier polymer, or introduced to the hot melt in the extruder via a side feeder. As the blend passes down the extruder barrel, the rotating screws ensure thorough mixing and the dispersion of agglomerates. At the end of the barrel, the blended, molten material is forced through holes in a die, much like a spaghetti maker, to create multiple strands. These strands are cooled, usually by passing them through a long water bath, before they enter a pelletiser that cuts the strands into small pellets, of similar dimensions to those of the original polymer. Once pelletised, the material is dried and bagged.
Some materials are adversely affected by water, which precludes the use of a conventional water bath. In these instances, a conveyor with air blowers is employed.
In addition to plastics, antimicrobial masterbatch can also be used in other materials, such as silicone. For these materials, the masterbatch is more likely to be made using a z-blade mixer or “mixtruder” which kneads the additives into the bulk silicone dough, before extruding it into a continuous bar.
What other additives can be incorporated into an antimicrobial masterbatch?
Including other additives is generally straightforward. Pigments, processing aids and technical fillers such as x-ray or metal detectable additives can easily be introduced during the same extrusion process. It is important to consider potential interactions between the different additives, such as pigments and silver ion antimicrobial, along with the effect on physical properties.
What does an antimicrobial masterbatch look like?
In most cases, an antimicrobial masterbatch will be very similar to the standard polymer: small, cylindrical pellets measuring 2-3mm long and 2-3mm diameter. For some applications, it can be desirable to have smaller pellets, or ‘micro-pellets’, or even for the masterbatch to be in the form of a coarse powder.
Since antimicrobial masterbatch can be produced for any polymer, silicone or rubber, the applications are essentially unlimited. Antimicrobial materials are frequently used in many sectors, including healthcare, consumer goods, food processing, construction, textiles, aerospace and automotive, in products as varied as breath monitors, refrigerators, conveyor belts, wall cladding and sportswear.
