Halloysite clay: fool’s gold or a nanomaterial mother lode?

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June 23, 2006 – The story of a little nanotech company in Rochester, N.Y., caused a lot of excitement recently when a newspaper wrote about a new type of paint that could use copper filled nanotubes to block cell phones signals, ostensibly creating a much-longed-for way to prevent annoying ring tones from interrupting meetings, movies and candlelit dinners.

The two-year-old company, called NaturalNano, doesn’t actually make the paint and is still researching the many applications for its nanotube technology. In fact, the company’s claim to fame is not that its nanotubes can be used to block radio frequencies, but that the tubes themselves are a naturally occurring material found in a halloysite clay mine in Utah.

“What’s exciting about these nanotubes is that they exist in the earth and people were completely unaware of them,” said Michael Riedlinger, president of NaturalNano. “Nature is a master of nanoscale manipulation, and there are likely many more sources for these naturally occurring nanotubes that are yet to be discovered.”

The mine’s halloysite clay has historically been used to make fine china and ceramics. A few years ago, one of the ceramics manufacturers wanted to find out what made this clay produce such delicate yet durable china. Its ensuing research showed that the clay was filled with millions of nanotubes that held interesting properties.

The halloysite nanotubes are ultra-tiny hollow tubes with diameters smaller than 100 nanometers. They range in lengths from about 500 nanometers to over 1.2 microns. But unlike carbon nanotubes, they are composed of aluminum, silicon, hydrogen and oxygen and are formed naturally in the Earth by surface weathering of aluminosilicate minerals.

“The result is a natural nanotube that is extremely good at storage and for controlled release uses,” Riedlinger said.

That storage capacity is what makes the nanotubes intriguing, says Emmanuel Giannelis, the Walter R. Reed professor of engineering and director of materials science and engineering at Cornell University. Giannelis, who is recognized as a pioneer in polymer nanocomposites, said that while organic materials from clay have been used in polymers for years, the discovery of nanotubes in the clay offers intriguing new possibilities. “The halloysite nanotubes appear to perform as well as clay composites with the added benefit that you can load them with various materials to add additional function with minimal impact,” he said.

The tubes have many potential applications, according to the company. They can be coated with metallic and other substances to achieve a wide variety of electrical, chemical, and physical properties, and they can be filled with such things as coatings, antifouling paint, antiscalants, pesticides, fragrances, pharmaceuticals, and other agents that could benefit from a controlled release. They might one day be used for odor masking in household products or to add scents to cosmetics; to create lighter weight durable plastics and polymers for cars, airplanes, and computers; to developing timed-release drug delivery using non-synthetic delivery vehicles; and of course, to create radio frequency blocking paints.

The paint, said Riedlinger, could be made by filling the hollow nanotubes with signal blocking copper then blending them into regular paints. The properties of the paint would remain unchanged and could be used on any wall to create spaces that block radio frequency signals.

While perhaps not the most compelling application, Riedlinger thinks there was excitement about the paint because it gave consumers a tangible way to imagine how nanotechnology research could directly impact their lives.

While these applications may not all result in marketable products, Giannelis believes that they are all feasible. “This is realistic science and these are sound uses for natural nanotubes,” he said. He also expects them to be cheaper than carbon nanotubes to use. “Because of the potential price advantages, it’s likely that researchers will pursue these applications.”

Giannelis is most excited about using the natural nanotubes to add antimicrobials, pesticides and flame retardants to other materials, but admits that has more to do with his own work at Cornell in these fields. “These applications resonate with me,” he said.

In the meantime, NaturalNano has already licensed technology that allows for selectively turning on or off access to radio signals, such as those used by cell phones or wireless computer networking devices, which is the next step in enabling the company to market the copper loaded halloysite nanotubes as a radio frequency shielding product. He doesn’t expect any paint product using the halloysite clay nanotubes to hit the market for at least two years.


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