Silver – and other – nanoparticles in fabrics

Nanotechnology has been discovered by the textile industry  – in fact, a new area has developed in the area of textile finishing called “Nanofinishing”.   Making fabric with nano-sized particles  creates many desirable properties in the fabrics without a significant increase in weight, thickness or stiffness, as was the case with previously used techniques.    Nanofinishing techniques include: UV blocking, anti-microbial, bacterial and fungal, flame retardant, wrinkle resistant, anti-static, insect and/or water repellant and self-cleaning properties.

One of the most common ways to use nanotechnology in the textile industry is to create stain and water resistance.   To do this, the fabrics are embedded with billions of tiny fibers, called “nanowhiskers” (think of the fuzz on a peach), which are waterproof and increase the density of the fabric.  The Nanowhiskers can repel stains because they form a cushion of air around each cotton fiber. When something is spilled on the surface of the fabric, the miniature whiskers actually cohesively prop up the liquid drops, allowing the liquid drops to roll off.   This treatment lasts, they say, for about 50 home wash cycles before its effectiveness is lost.  A corollary finish is that of using nanoparticles to provide a “lotus plant” effect  which causes dirt to rinse off easily, such as in the rain.

Nanotechnology can also be used in the opposite manner to increase the ability of textiles, particularly synthetics, to absorb dyes. Until now most polypropylenes have resisted dyeing, so they were deemed unsuitable for consumer goods like clothing, table cloths, or floor and window coverings. A new technique being developed is to add nanosized particles of dye friendly clay to raw polypropylene stock before it is extruded into fibres. The resultant composite material can absorb dyes without weakening the fabric.

The other main use of nanoparticles in textiles is that of using silver nanoparticles for antimicrobial, antibacterial effects,  thereby eliminating odors in fabrics.  Nanoparticles of silver are the most widely used form of nanotechnology in use today, says Todd Kuiken, PhD, research associate at the Project on Emerging Nanotechnologies (PEN). “Silver’s antimicrobial property is one that suits a lot of different products, and companies pretty much run the gamut of how many consumer products they put it in.”

PEN’s database of consumer products that contain nanoparticles lists 150 different articles of clothing, including athletic clothes,  jogging outfits, camping clothing, bras, panties, socks, and gloves, that are treated with nano-silver because it kills the bacteria that cause odor.

The future for textile applications using nanotechnology is exploding due to various end uses like protective textiles for soldiers, medical textiles and smart textiles.  Consider the T-shirt.  Research is being done that will use nanotechnology-enhanced fabric so the T-shirt can monitor your heart rate and breathing, analyze your sweat and even cool you off on a hot summer’s day.  What about a pillow that monitors your brain waves, or a solar-powered dress that can charge your ipod or MP4 player?  The laboratory of Juan Hinestroza, assistant professor of Fiber Science and Apparel Design at Cornell University, has developed cotton threads that can conduct electric current as well as a metal wire can, yet remain light and comfortable enough to give a whole new meaning to multi-use garments. This technology works so well that simple knots in such specially treated thread can complete a circuit – and solar-powered dress with this technology literally woven into its fabric.  Dr. Hinestroza designed the fabrics used in a Cornell Univesity fashion show by designer Olivia Ong,  which guards the wearer against bacteria, repels stains, fights off allergies and oxidizes smog.  And costs about $10,000 per yard to make.

And yet, there is mounting evidence that nanotechnology requires special attention.   Here’s an excerpt from an interview with Andrew Maynard,  science advisor to the Project on Emerging Technologies (PEN), from Technology Review:

• “Individual experiments have indicated that if you develop materials with a nanostructure, they do behave differently in the body and in the environment.

• We know from animal studies that very, very fine particles, particles with high surface area, lead to a greater inflammatory response than the same amount of larger particles. We also know that they can enter the lining of the lungs and get through to the blood and enter other organs. There is some evidence that nanoparticles can move into the brain along the olfactory nerve, so this is completely circumventing the blood-brain barrier.

• There really isn’t any consensus on how you go about evaluating the risks associated with carbon nanotubes yet. In cell cultures, you have to have some idea what kind of response you’re looking for. We already know in some studies that the lungs see carbon nanotubes almost as biological materials–they don’t see it as a foreign material. But then because of that, they start building up layers of collagen and cells around these nanotubes. They almost see them as a framework for building tissue on. Now, that actually may be a good thing in parts of the body, but in the lungs you end up using up the air space. But without that information, you wouldn’t necessarily know what were the appropriate cell tests to do in the first place.

• The thing that concerns me is, there is very much a mind-set that is based on the conventional understanding of chemicals. But nanomaterials are not chemicals. They have a structural component there as well as a chemical component.

At the recent meeting of the Society of Environmental Toxicology and Chemistry (SETAC), more than 20 studies were presented on the fate of nanoparticles once they enter the environment, and nearly all found that these materials were building up in organisms, such as earthworms, insects, and fish, and having subtle effects on their abilities to survive

The Environmental Protection Agency (EPA) is poised to grant it’s first-ever approval to use nanosilver particles in fabrics.  The approval is “conditional”, meaning that the manufacturer must provide test results (within four years) showing how the nanosilver particles interact with the environment.  However, the EPA has a long history of letting such approvals linter, and has already expressed concern about nanosilver particles impacts on health, saying the approval “will likely lead to low levels of human and environmental exposure and risks.”

Last year, the Swiss Federal Laboratories for Materials Testing and Research examined what happens to silver nanoparticles in fabrics during washing – and found that these silver nanoparticles actually wash out of fabrics – so there is a high likelihood that the silver will spread into the environment. Another study found that socks treated with nanosilver lost, on average, half the nanoparticles embedded in the fabric during washing.

Among other well documented studies (see sites listed below) which have shown silver nanoparticles to be highly toxic to bacteria, fungi and other microorganisms is one by Duke University,  in which it was found that silver nanoparticles negatively impacted the growth of plants – and also kills the beneficial soil microbes which sustain the plants.  “Nanoparticles likely enter the environment through wastewater, where they accumulate in biosolids (sewage sludge) at wastewater treatment plants. One of the ways in which the sludge is disposed of is through land application, because it is valuable as a fertilizer. Whereas fertilizers add nutrients to the soil that are essential for plant growth, plants also depend on soil bacteria and fungi to help mine nutrients from the air and soil. Therefore, the antimicrobial effects of silver nanoparticles could have impacts at the ecosystem level—for example, affecting plants whose growth is dependent on soil-dwelling microorganisms.”  Another study (Choi, Yu, Fernandez et al in Water Research 2010)  found that once nanosilver is washed down the drain, it’s highly effective at killing the microorganisms used to treat sewage in wastewater treatment plants, which could lead to bigger problems with drinking-water safety.

The Rodale website  had some suggestions for those of us who are worried about smelly clothes:  Try nature and a little common sense.

• Pretreat. Before you wash your smelly gym clothes, sprinkle some baking soda on them, leaving it on for about an hour before laundering them to remove perspiration odors as well as stains.

• Launder with care. Because sweat can be oily, it can build up on clothing, becoming difficult to remove with regular detergents and water. Add a cup of white vinegar to the rinse cycle; vinegar helps break through oils on fabric, and it serves as a deodorizer. Or hand-wash your clothes with shampoo, which is designed to cut through body oils.

• Line-dry. Nothing cuts through bad odors like oxygen and sunlight. Let your clothes dry outside, rather than in a machine, and you’ll save energy, make your clothes last longer, and prevent offensive odors the next time you hit the gym. Read our Nickel Pincher’s line-drying story for the ultimate in line-drying advice.

Some other studies on toxicity of nanoparticles:

http://www.scientificamerican.com/article.cfm?id=nanotechnology-silver-nanoparticles-fish-malformation

http://www.nanotech-now.com/news.cgi?story_id=34185

http://nanosafety.ihep.ac.cn/2006/2006.15.pdf

http://www.klgates.com/files/Publication/2b1f4c2a-298b-4948-9ce7-69f1396b61ac/Presentation/PublicationAttachment/bbdf8cdc-be42-4fa6-b942-7263b449d0b3/Article_Stimers_Nanotech.pdf