There are many options to weigh when considering which antimicrobial is best for a particular product. Application method is an important aspect to examine in more detail.
According to Damien Fruchart, textile engineer with Asix International Development Consultancy, there are three main options for applying an antimicrobial agent to textiles. Each has its own advantages and challenges.
The first option is treating the fabric through an "aqueous process" in the finishing line with the antimicrobial substance. The second is incorporating the antimicrobial into or onto the fiber itself. A third application method, according to Fruchart, is post-consumer, "an additive designed to be added to the laundering water each time the product is washed."
Applied to the Fabric
The benefit of topical antimicrobial treatment applied to the fabric during the finishing stage is that "Topical application is more versatile," says Jeff Trogolo, chief technology officer for antimicrobial supplier Agion. "It's later in the process and gives the retailer more flexibility about which fabric to choose." A topical antimicrobial finish is appropriate for any use that uses a relatively small amount of fabric, or one that mixes many different fiber types, Trogolo says.
Washfastness is key, says Hirotoshi Goto, professional engineer JP for fabric supplier Toray Industries. In Japan, the standard for wash durability is 50 washes at 80C for industrial laundering such as hospitals. For non-hygiene-critical applications such as home laundering, 20 washes at 40C is considered standard. Washfastness can be improved through the use of a highly durable resinous binder, which has better affinity with the agent and fiber and works like an adhesive, says Goto. "But this kind of resin is hydrophobic, and will give new problems," he says. Issues may include residual formaldehyde, or a fabric that is unable to absorb perspiration.
Goto says that a new method used by his company applies the antimicrobial as a fabric finish without a binder. Instead, the antimicrobial infiltrates into the synthetic fibers in a manner similar to a disperse dye. "This agent has especially high affinity with polyester fiber," says Goto.
Another challenge of using topical antimicrobial finishes, says antimicrobial consultant William D. Hanrahan, is that "each individual fiber and fiber blend has its own chemistry and its own way of being finished. You have to make sure that the antimicrobial doesn't interfere with any other finishes being applied to the fabric, and that the characteristics of the fabric-hand, water repellency, fire retardance-aren't changed."
Applied to the Fiber
Applying the antimicrobial directly into the fiber master batch during synthetic fiber formation is also popular. According to Hanrahan, adding the antimicrobial at the fiber stage narrows the field of antimicrobials that can be used because synthetic fibers are commonly extruded at high temperatures. This rules out most organic antimicrobials says Mark Wiencek of Milliken, because many are not thermally stable. "They may lose some of the active ingredients. Incorporation of antimicrobials into textile fibers during the spinning process (often via a master batch) is an application dominated by silver. This is because silver is thermo-stable," he says.
"Antimicrobial agents blended into the fiber can show superior washing durability, but take longer to work," says Goto. He also says that, since many of the fiber-application systems are metal-based antimicrobials, the color of the fiber can sometimes be affected.