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Nanotech Plastic Textile Dissipates Body Heat

Samples of heat-emitting materials

Samples of heat-emitting textile and intermediate materials (L.A. Cicero, Stanford University)

2 September 2016. A new plastic textile material developed at Stanford University is shown to reflect sunlight while allowing more heat from the body to escape, keeping people cooler. Researchers from the lab of materials science professor Yi Cui describe their discovery in today’s issue of the journal Science.

Cui and colleagues are seeking a material for clothing that helps keep people cooler, which could translate into less use of air conditioning and fewer carbon emissions from burning fossil fuels for electricity. “If you can cool the person,” says Cui in a university statement, “rather than the building where they work or live, that will save energy.” In fact, funding for the project came from Advanced Research Projects – Energy, or ARPA-E, part of the U.S. Department of Energy.

The Stanford team, joined by colleagues from SLAC National Accelerator Laboratory in Menlo Park, California, applied photonics, the study of light and energy, to the problem. The researchers investigated the interaction of heat from the human body emitted as invisible infrared radiation with light waves in the visible part of the spectrum. Regular fabrics, such as cotton, may block sunlight and allow perspiration to evaporate, but they often trap infrared radiation as well, preventing it from escaping and making the body feel warmer.

For a solution, the team looked into nanoporous form of polyethylene, a polymer plastic most commonly found in kitchen plastic wrap. In this case, nanoporous polyethylene has interconnected pores from 50 to 1,000 nanometers in diameter; 1 nanometer equals 1 billionth of a meter. At this size, the pores are comparable in size to visible light waves — 400 to 700 nanometers — which still enables the material to reflect back light. But the pores still make the polyethylene transparent to infrared, allowing radiation to escape and reducing the heat felt by the skin.

Cui’s lab, which conducts research on materials for batteries, started with a commercially-available nanoporous polyethylene used in batteries. That material has a structure that blocks visual light but still allows infrared radiation to pass through. The researchers then modified the chemical structure of the polyethylene to resemble more of a fabric, including the ability to let perspiration evaporate through the pores. The result was a thin nanoporous polyethylene, which the team configured into a textile, with 2 layers of nanoporous polyethylene separated by cotton mesh for strength.

The team tested the textile material with a device developed in the lab that simulates the skin’s heat output. The device includes a heating element that generates a constant temperature, with space for insertion of material swatches to measure the heat retained. The results show simulated bare skin temperature at 33.5 degrees C (92.3 F), and a swatch of the test material slightly higher at 34.3 C (93.7 F). By comparison, the heat retained by cotton measures at 37.0 C (98.6 F), even warmer than the home insulating and packaging material Tyvek at 36.4 C (97.5 F).

Cui and several co-authors filed a patent application for the discovery, but are still improving on the product and its manufacturing process. “If you want to make a textile, you have to be able to make huge volumes inexpensively,” Cui notes. To that end, he and lab colleagues are adding more colors and textures, as well as properties more like natural cloth fabrics to their material.

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