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.
Hanrahan says that another limitation of this application is that the retailer loses flexibility, because the antimicrobial is added far back into the supply chain. "It means you have to carry inventory. And the product may be marked up along the supply chain," he says. "This application tends to be more durable, but not as economical." According to Trogolo, this kind of application is best for end-uses that need large amounts of one kind of fiber, such as upholstery or uniforms.
Other ways of applying antimicrobials to textiles are less common. Noble Biomaterials' X-Static product is a "universal and permanent coating of silver on substrates from yarn to fabric," says the company's Chief Commercial Officer, Joel M. Furey. This system is "primarily intended where users need high levels of performance," says Furey. This means "high kill rates of bacteria and fungi with a fast kill action," he says.
Another product with a high kill rate is chlorine. According to Wiencek, n-halamine binders "have a unique way of dealing with antimicrobial treatments-they bind chlorine to the fabric, so that they can make claims that EPA-registered chlorine bleach can make." According to Fruchart, chlorine is "as good as any disinfectant. A 99.9% killing rate is reached within an hour, which is quicker than most other aqueous treatments." This is Fruchart's post-consumer after-treatment method.
The chlorine is used as an antimicrobial and is recharged onto the fabric by adding chlorine bleach to the laundry. A drawback to this system, says Wiencek, is that although this technology is intended for niches that require industrial laundering, not all industrial laundries use chlorine-based bleach.
Fruchart remarks that in a laminated product, "instead of treating the fabric, an antimicrobial agent is added in the adhesive. The active ingredient will radiate, thus creating an inhibition zone, while remaining resistant to laundering." Adhesive treatment makes it possible for laminated polyester fabric to maintain an antimicrobial activity despite prolonged washing cycles.
In a similar vein, Fruchart notes that "one technique, although not frequently used, consists of placing antimicrobial agents contingent in between two membranes. The membranes' permeability allows the controlled release of active ingredients, which migrate to the surface. This type of process is mainly....for products that do not get laundered, like mattress covers and separation curtains. With complementary methods, protection can last for several years."
A flexible technology like the Aegis SiQuat can be applied in or onto fibers, fabrics, or post-consumer laundry treatment, says Bob Montincello of Aegis Environments. "This versatility in application provides textile mills with options... [that] keep down costs and maximize performance," he says.
"The best application procedure for antimicrobial treatment will provide for mill qualification testing and good, solid SOPs, along with quality assurance procedures that are based upon useful chemical analytical and microbiological tests," says Curt White of Aegis Environments.
Does the Application Matter?
Depending on the product's end-use, the marketing claims made, the antimicrobial's chemical and physical properties, and its mode of antimicrobial activity, the antimicrobial's application does matter.
Some antimicrobials can be applied in several ways, but other technologies are limited to one mode of application. A product designer's main priorities, whether for flexibility, durability, cost, compatibility with other finishes, spectrum of microbes to be fought, or high-performance, may influence the application, and the antimicrobial, chosen to protect that product. Application matters!
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