Page 65 - Plastics News May 2017

TECHNOLOGY

A low-cost plastic material could result in clothing that cools the wearerT

tanford engineers have developed a low-cost, plastic- material: It allows thermal radiation, air and water vapor
Sbased textile that, if woven into clothing, could cool your to pass right through, and it is opaque to visible light. The
body far more efficiently than is possible with the natural easiest attribute was allowing infrared radiation to pass
or synthetic fabrics in clothes we wear today. Describing through the material, because this is a characteristic
their work in Science, the researchers suggest that this new of ordinary polyethylene food wrap. Of course, kitchen
family of fabrics could become the basis for garments that plastic is impervious to water and is see-through as well,
keep people cool in hot climates without air conditioning. rendering it useless as clothing. The Stanford researchers
If you can cool the person rather than the building tackled these deficiencies one at a time.
where they work or First, they found a variant of polyethylene commonly
live, that will save used in battery making that has a specific nanostructure
energy,” said Yi Cui, that is opaque to visible light yet is transparent to
an associate professor infrared radiation, which could let body heat escape.
of materials science This provided a base material that was opaque to visible
a n d e n gin e e rin g light for the sake of modesty but thermally transparent
at Stanford and of for purposes of energy efficiency. They then modified
photon science at SLAC the industrial polyethylene by treating it with benign
National Accelerator chemicals to enable water vapor molecules to evaporate
Laboratory. This new through nanopores in the plastic, said postdoctoral
material works by scholar and team member Po-Chun Hsu, allowing the
allowing the body to plastic to breathe like a natural fiber.
discharge heat in two ways that would make the wearer
feel nearly 4 degrees Fahrenheit cooler than if they wore That success gave the researchers a single-sheet material
cotton clothing. The material cools by letting perspiration that met their three basic criteria for a cooling fabric. To
evaporate through the material, something ordinary fabrics make this thin material more fabric-like, they created
already do. But the Stanford material provides a second, a three-ply version: two sheets of treated polyethylene
revolutionary cooling mechanism: allowing heat that the separated by a cotton mesh for strength and thickness.
body emits as infrared radiation to pass through the plastic To test the cooling potential of their three-ply construct
textile.All objects, including our bodies, throw off heat versus a cotton fabric of comparable thickness, they
in the form of infrared radiation, an invisible and benign placed a small swatch of each material on a surface that
wavelength of light. Blankets warm us by trapping infrared was as warm as bare skin and measured how much heat
heat emissions close to the body. each material trapped. “Wearing anything traps some
heat and makes the skin warmer,” Fan said. “If dissipating
This thermal radiation escaping from our bodies is what thermal radiation were our only concern, then it would be
makes us visible in the dark through night-vision goggles.“40 best to wear nothing.” The comparison showed that the
to 60% of our body heat is dissipated as infrared radiation cotton fabric made the skin surface 3.6 F warmer than
when we are sitting in an office,” said Shanhui Fan, a
professor of electrical engineering who specializes in their cooling textile. The researchers said this difference
photonics, which is the study of visible and invisible light. means that a person dressed in their new material might
“But until now there has been little or no research on feel less inclined to turn on a fan or air conditioner.
designing the thermal radiation characteristics of textiles.” The researchers are continuing their work on several
To develop their cooling textile, the Stanford researchers fronts, including adding more colors, textures and cloth-
blended nanotechnology, photonics and chemistry to give like characteristics to their material. Adapting a material
polyethylene – the clear, clingy plastic we use as kitchen already mass produced for the battery industry could
wrap – a number of characteristics desirable in clothing make it easier to create products.

65 May 2017 | Plastics News