From the fiber level to surface coatings, new developments in nanotechnology impact many specialty fabrics markets.
Ways of manufacturing specialty fabrics have been around for decades, but what does that mean in terms of opportunities for manufacturers, particularly in regard to coatings? Current applications include military camouflage clothing that can change color as a function of the environment, textiles that capture bacteria in mass transportation systems and textile filtration devices that lower toxic emissions from industrial manufacturers. And that’s only the beginning. Scientists involved in research and development of nanotechnology and textiles have a lot to say about where this phenomenon may be headed and what the applications are for companies rolling out textile products.
Manipulating the molecules
Nanotechnology has to do with any object with dimensions below 100 nanometers. When dealing with fabrics and coatings, nano-scale technologies can be used in coatings or at the fiber level. “What we do in our laboratory has to do with two things,” says professor Juan P. Hinestroza, associate professor of fiber science and director of the Textiles Nanotechnology Laboratory at the College of Human Ecology of Cornell University, Ithaca, N.Y.
“One of the things we do is to use objects that have those dimensions [below 100 nanometers] to coat existing fibers, such as cotton, polyester and nylon. But also the same [nanotechnology] term can apply to making fibers with smaller diameters—less than 100 nanometers.
“The first aspect [coatings] is where we modify the existing materials to make them behave in a way that they don’t like to behave,” Hinestroza says. “For example, we make cotton conduct electricity and/or kill bacteria or create color without using dyes. These are properties we can manipulate by controlling the interfaces between the small materials and existing materials.”
The other aspect—manipulating the size of fibers—results in capturing particles in the air. “We developed technology to capture industrial toxic chemicals as well as chemical warfare agents,” Hinestroza says. “This is possible because of the combination between the small molecules we developed and the small size of the fibers.”
The environmental dangers associated with the use of fluorocarbons are driving scientists to find new ways to coat fabrics for soil and oil resistance. “The international restrictions of fluorocarbons were the main reason for our investment and development activities,” says Oliver Sonntag, head of international sales of Nano-Care AG, Saarwellingen, Germany. “By the latest technologies it is now possible to manufacture environmentally friendly and food-safe textile finishings that have no impact on the touch—or feel—of the textile. These finishings are based on a natural raw material: silicon dioxide [SiO2].
“Due to their nonstick characteristics, they can save cleaning efforts. Furthermore, they come in water-based solutions so they are environmentally friendly and easy to handle regarding worker protection.” Sonntag points out additional benefits that are the result of SiO2 coatings’ ability to be delivered in concentrated forms: shipping cost savings and, in turn, reduced CO2 emissions.
Using the sol-gel method (a chemical process that deposits coatings on a substrate) Nano-Care is developing self-drying SiO2, that is ultra thin; the average coating size is 100 nanometers. Because the finishes dry at room temperature and are easily applied (by spraying), Nano-Care expects the product to be marketed to consumers as dirt protection for home textiles.
One step further than coatings that repel stains is bacteria-killing coatings. Dr. Manfred Heuberger, head of the Laboratory for Advanced Fibers at Empa, an interdisciplinary research and services institution for material sciences and technology in Switzerland, is working on a nano-composite coating with antimicrobial properties. “We have implemented the generation of a novel nano-composite coating using plasma technology,” Heuberger says. “While a thin polymer layer is grown on a surface, nanoparticles of silver are produced inside the polymer layer. These coatings have strong antimicrobial action during short times—hours to days—until all silver is consumed. Hence, no silver is wasted and only very small overall amounts of silver are used, which makes this method economical and environmentally friendly.”
Perhaps a clue to what some applications might be for nanotechnology and textile coatings lies in who’s funding the research. “We get a lot of funding through the Department of Defense, Department of Commerce, the National Science Foundation and the Defense Threat Reduction Agency,” Hinestroza says. “And now more and more we are getting funding from overseas.”
Military and threat reduction applications are among those currently in use, products that protect users from contaminants and provide high-tech camouflaging properties.
“We’ve developed technology to capture industrial toxic chemicals as well as chemical warfare agents,” Hinestroza says. “Companies take our technologies to incorporate them into products such as uniforms and tents that can capture gases, and for filters in mass transportation.”
Hinestroza’s work is also used in military interactive camouflage. “Interactive camouflage is clothing that can change color as a function of the environment,” he says. “If you are in the jungle the uniform becomes greenish and if you’re in the desert it becomes a sandy color.” The color change is a result of controlling the interactions between the particles and the light.
Dr. Joshua Windmiller, who completed his postdoctoral fellowship in the Department of Nanoengineering at the University of California, San Diego, in June, founded his own company shortly thereafter—Electrozyme LLC. The company is working to print biosensors directly on the surface of textiles, using inks that provide chemical selectivity toward various compounds of interest. Products the company is working on include those for fitness assessment healthcare monitoring and environmental sensing.
“We’ve developed a wetsuit that contains sensors to detect contaminants in sea water,” Windmiller says. “The sensors have the ability to quantify trace heavy metals such as copper, arsenic and lead, in real time, as well as the ability to detect underwater munitions and explosives, and pollutants such as phenols.”
New printing techniques
Printing techniques for applying nano-coatings to textiles are as much a part of the research and development as the coatings themselves. “Since the sensors are printed, they’re intrinsically very low in cost,” Windmiller says. “The printing technique we leverage is analogous to screen printing except that our inks are effectively nano-engineered to be chemically selective toward various analytes of relevance to the application. By printing on clothing, we can enable a centralized sensing platform directly on the body.”
As a part of his research, Hinestroza also works with 3-D printing, “to assemble the molecules on top of the fibers,” he says. “Before we had to immerse the fabric or the fiber into a solution that had the molecules we wanted to attach. Now with this technology, we can print the molecule on top of the fiber and we can layer one on top of another.” He cites the benefits of printing as the ability to produce small batches for samples and the ability to apply coatings to only those areas intended to perform a specific function. For instance, odor-fighting coatings can be applied to the underarms of a T-shirt and UV-resistant coatings to the remainder of the shirt.
As with any new technology, there are concerns about what the long-term effects of the products and processes will be. “There is an ongoing discussion about the safety of nanotechnology, which strongly affects market introduction,” Heuberger says. “Manufacturers and consumers consider the reputation of nanotechnology in the society, which has become a delicate balance between the fear of adverse effects and the enthusiasm for new opportunities. Scientists know today that nanotechnology is a safe technology if basic precautions are taken.”
Windmiller agrees. “Extensive research that has been conducted in the safety of nanotechnology has yet to suggest that this class of compound is deleterious to your health,” he says. “Moreover, in most applications these materials are embedded in polymers that effectively entrap and aggregate these compounds so there’s a minimal risk of leaching from the matrix.”
From possibility to product
Taking products from the lab to the consumer requires initiative and the manufacturers’ own brand of research. Sometimes manufacturers work directly with scientists in the lab but most often the product development work happens after the discoveries are made. “Most of the time we work with small companies that can translate these discoveries from the lab to large production scale,” Hinestroza says. “They only need access to a specific discovery, so we develop the process and the company licenses the patent.” Hinestroza advises that the best—and most common—way to develop products based on the discoveries is for the manufacturer to hire the student who was working on the project.
Nanotechnology and textile coatings are a continually emerging reality with seemingly limitless opportunities on the horizon. They can seem too daunting for small companies to consider, but when the need, the technology and the price fit they can be a turning point for companies and clients as well. “In the long run, we will find nanotechnology only in products if there clearly is added value and where the cheaper conventional alternatives have disadvantages,” Heuberger says.