Polymer-based technologies offer new opportunities for microbial control on textiles.
by Robert A. Monticello, Ph.D.
Ever since microorganisms were recognized as a major cause of problems on textiles people have struggled against them in an effort to provide clean, pleasant and odor-free textile products that can be kept close to the skin. An array of cleaners, chemicals, devices and methods combat microbial problems caused by organisms, from fungi to pathogenic bacteria.
But polymer-based antimicrobial products, particularly for odor control in textiles, function quite differently. The key is the biocides’ release rate. With integration into polymer systems that release only active ingredients, very low levels need to be used. Particle-based products release metallic silver, silver ions and the particles themselves. These polymer-based antimicrobial products for textiles are not nanosilver particles. In fact, they are not particles at all, which is how this material is fundamentally different.
Microbial contamination of textile products is a major problem, not only in the hospital environment but in the everyday use of fabrics. While bacterial cross-contamination and the risks associated with Hospital Acquired Infections (HAI) are pronounced, odor control and excessive deterioration of everyday fabrics are a common and significant concern.
At their best, these versatile, varied and prolific organisms aid people as they provide a source of food and help develop and form our bodies’ immune systems. At their worst, microorganisms cause deterioration of useful materials, stains, odors and disease. Microbes function by a variety of physical and biochemical mechanisms, but they must have moisture, food, proper temperatures and receptive surfaces to function and reproduce. Textiles that are worn close to the skin or otherwise used or stored in hot and humid environments provide an ideal environment for microbial growth.
Antimicrobials are used on textiles to control bacteria, fungi (mold and mildew), and algae, which are the organisms that cause textile deterioration, staining and odors, as well as health concerns. There are both good and bad types of microorganisms. Control strategies of bad organisms must include being sure that nontarget organisms aren’t affected. For instance, antimicrobial agents applied to textiles must control all microorganisms on the textile without leaching into the environment and affecting the natural biological skin flora.
Controlling microbial growth on textiles to both reduce unsightly growth, odor and microbial deterioration has been possible for decades. Technologies used to control this bacterial growth have expanded over the past 30 years just as the technology used to produce these fabrics has expanded. The antimicrobial agent Triclosan, for example, has been used in everything from toothpaste to underwear. Concerns about the uncontrolled release rate, microbial adaptation and bioaccumulations have forced the industry to move to safer and more effective technologies.
The use of silver on textiles for the control of odor-causing organisms has grown substantially in the past 20 years. Current silver technologies are particle based and rely on the continuous release of silver which is controlled by varying either the particle size (nanoparticles/microparticles) of the silver or the release rate of the particle from the surface of the textile. Reducing the environmental footprint of these treated articles starts with reducing the amount of silver and the silver particles (nano or micro sized) that could potentially be released from the treated article.
As textiles become more advanced and are used in more diverse applications, and considering the increased environment exposure of these agents, greater care in choosing the proper antimicrobial agent for a given application is warranted.
The polymer alternative
Polymer antimicrobial technologies offer unique opportunities for the delivery of antimicrobial properties onto a variety of textiles surfaces. Polymers with the ability to integrate into a variety of substrates, such as nylon, polyester, cotton or wool under both pad and exhaust conditions, offer opportunities for the production facility and provide a durability profile not commonly experienced in the textile industry without the addition of large amounts of active ingredients or additional binding systems.
In the past, quaternary silanes were used to form polymeric structures on textiles manufactured to control bacteria on surfaces in a more environmentally sensitive manner. The individual silane monomer could create a surface layer of protection that would react both with itself and with the textile surface to create an extremely durable antimicrobial coating that does not need to be released to sufficiently kill bacteria on contact. While effective and durable when properly applied, quaternary silane technology can be difficult to manipulate because of its cationic nature, and it can cause problems in the manufacturing setting. Furthermore, since the technology is well known, many manufacturers produce slightly different products that can affect the overall activity of the final treated product.
Antimicrobial polymer systems that optimize effectiveness while reducing the release rate of the active ingredient into the environment provide a much smaller environmental footprint. Recent advances in polymer technology have produced new delivery systems for silver ions. This new polymer technology, Silvadur™ from Dow Chemical, comprises silver ions and a proprietary polymer that forms a strong silver-polymer complex when applied to a textile. On the treated surface, an equilibrium state is quickly established between silver ions that are bound to the polymer and those that are free. The free silver ions on the surface effectively kill the odor-causing bacteria on the textile surface as they attach to the textile. As the surface is depleted of these silver ions, the complex releases others to maintain the equilibrium. This system is not based on the application of particles, but the association of the silver-polymer complex and equilibrium release of the active ingredient. In this form, and due to the fact that only silver ions are released, up to 100 times lower levels of silver are needed to be completely effective.
With the changes in antimicrobial technologies used on textiles, microbiologists have had to change the way they measure this activity on the treated surface. Originally, microbiologists would measure the distance to which the active ingredient “leaches” from the treated surface using standard “Zone of Inhibition” assays. The most common method used is the AATCC 147. This method is not applicable to the polymer technologies fully associated with the fabric surface and release little to no active ingredient away from the surface of the treated good.
The most common antimicrobial test method involves a direct inoculation of a treated surface with a known concentration of bacteria. After a designated time (usually 18-24 hours), the fabric is removed and remaining bacteria are counted. This method has many variations, but the most common include the ISO 20743 or AATCC 100 methods.
Advances in microbial control
Many technologies are available to control bacteria on the textile surface. Polymer technologies offer the unique ability to uniformly coat virtually any surface using standard finishing procedures within textiles mills. Polymer based antimicrobials allow very low levels of active ingredient to be used without the concern of releasing the active ingredient, which is generally seen with other antimicrobial technologies.
Consolidated Pathways Inc. (C-Path) is a member of the International Antimicrobial Council, which focuses on polymer antimicrobial systems. Its goal is to reduce the overall exposure of the environment to the potentially hazardous and uncontrolled release of antimicrobial agents that are added for odor control on textiles. In association with the major suppliers of polymer-based antimicrobial agents, C-Path provides education and direction in the storage, sourcing, application and microbiological testing for polymer-based, antimicrobial-treated articles.