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issue: May 2004 APPLIANCE Magazine

From the Top
Antimicrobial Surfaces for Appliances

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Dick Topping, director of Appliance Research, TIAX, LLC

You may have grown up listening to your mother’s insistent warnings about germs. “Don’t touch that; you don’t know where it’s been” and “wash your hands before you eat” are admonishments that most of us know well. Your mother probably wasn’t a microbiologist, but she was still on to something.

You may have grown up listening to your mother’s insistent warnings about germs. “Don’t touch that; you don’t know where it’s been” and “wash your hands before you eat” are admonishments that most of us know well. Your mother probably wasn’t a microbiologist, but she was still on to something.

Germs can make you sick. And they’re everywhere. Germs in the form of harmful bacteria, mold/fungi, and viruses are constantly challenging the body’s immune system—a challenge that effectively enables us to ward off disease. This system works well until new varieties of germs occur through natural mutation or until the concentration of germs becomes so high that we succumb to illness.

What does all this have to do with appliances? Plenty! Dishwashers, for example, use a combination of heat and detergents formulated with bleach and other antimicrobial chemicals to sterilize dishes. Washing machines use bleach, detergents, and enzyme products to clean and disinfect clothes. We sanitize our kitchen, laundry, and bathroom surfaces with formulated chemical products to destroy bacteria and fungi such as mold and mildew. We treat our humidifiers and dehumidifiers with sanitizing solutions to prevent microbial growth and cook our food according to U.S. Food and Drug Administration guidelines for eliminating bacteria in our ranges and microwaves.

That being said, is there anything else the appliance industry is able to do in defense of this microbial onslaught? To answer that, it is necessary to understand how germs operate. The natural life cycle of microscopic biological particles called “microbes” involves attachment and colonization on various surfaces. Once a microbe colonizes, it can grow and multiply exponentially, reaching harmful concentrations that can cause illness. In certain moisture-prone environments, colonized microrganisms form biofilms, which are breeding grounds for many different bacterial species. Biofilms generally contain such high numbers of microbes that conventional cleaning is powerless against them. It’s much better to prevent or inhibit the growth of biofilms in the first place. But how?

Stainless steel is one possibility. It is easily cleaned with formulated disinfectants and, when electropolished, has a natural ability to resist microbial attachment and the formation of biofilms. But as popular as stainless steel is today, it just isn’t feasible to use it in every appliance and every surface exposed to germs.

There is another potential solution. The fields of materials science, chemistry, and microbiology have collaborated in developing material surfaces that resist the formation of biofilms and, even better, incorporate antimicrobial properties into the surfaces themselves. Several exciting technologies have recently been commercialized, including coating systems that can be applied to metal and plastic to produce antimicrobial surfaces. One of these systems is based on the controlled release of silver ions, a biocide that has been used in soluble form in medical applications for many years. The new technology uses moisture to activate the release of silver ions entrapped in a zeolite (synthetic mineral) matrix. The silver ions then interact with and kill offending microbes.

For plastic surfaces that cannot be coated, progress has been made using “microencapsulation” to encapsulate organic chemical biocides—such as those used in many deodorants—into the plastic itself. The biocides slowly exude to the surface where they kill bacteria and inhibit the formation of biofilms.

Another new concept for coating surfaces uses technology based on the antimicrobial properties of zinc oxide and other metal oxides. Recent advances in nanotechnology have enabled the production of extremely small particles of zinc oxide, which, when incorporated into plastics and polymeric coatings, prevents the growth of biofilms.

This all may sound esoteric, but antimicrobial surfaces are already being implemented by the appliance industry. Makers of commercial ice machines now use antimicrobial materials in their machines. The treated surfaces inhibit the growth of bacteria, which is carried into the ice-holding area by water and air. Certain humidifying systems are also beginning to apply antimicrobial materials to deal with slime control.

Might these materials and technologies be broadly applied to home appliances and electric housewares to defend us from more germs and prevent microbes and mold from building biofilm in our homes? Yes—the technology is emerging. We expect that consumers—especially those mothers—will be very interested in the improvements that lie ahead.

Dick Topping

Dick Topping is director of Appliance Research at TIAX LLC (www.tiax.biz). He can be reached by phone at 617/498-6058, by fax at 617/498-7206, or e-mail at topping.r@tiax.biz.

From the Top appears bimonthly in
APPLIANCE Engineer™.


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