Scientists develop cool new fabric that reflects Sun and pushes out body heat

By Stephen Beech via SWNS

A new form of cooling fabric has been created using a chalk-based coating.

The "durable" coating cools air underneath the treated fabric by up to 8 degrees Fahrenheit, say American scientists.

While some textiles reflect the sun’s rays or transfer heat away from the body, current options require boutique fibers or complex manufacturing processes.

Professor Trisha Andrew, a chemist and materials scientist at the University of Massachusetts, Amherst , said: “If you walk out into the sunlight, you will get increasingly hot because your body and clothing are absorbing ultraviolet and near-infrared light from the sun.

“And as long as you’re alive, your body is generating heat, which can be thought of as light, too.”

To make people more comfortable outside, researchers have been developing textiles that simultaneously deflect the sun’s rays and push out natural body heat - a process known as "radiative cooling".

Andrew says some of those materials have light-refracting synthetic particles, such as titanium dioxide or aluminum oxide, embedded into spun fibers.

Others use organic polymers, such as polyvinylidene difluoride, which require perfluoroalkyl and polyfluoroalkyl substances - known as PFAS or "forever chemicals" - in their production processes to create light-reflective textiles.

However, Andrew said scaling the manufacturing of those materials for commercialization isn’t sustainable.

She challenged research team members Evan Patamia and Megan Yee to develop a textile coating that does the same thing using natural or environmentally benign materials.

Andrew and her colleagues previously created a simple technique to apply durable polymer coatings on fabric called chemical vapor deposition (CVD).

That method combines synthesis and deposition into the same step: grafting a thin polymer layer onto commercial textiles with fewer steps and less environmental damage than other ways to attach coatings.

Inspired by crushed limestone-based plaster used historically to keep houses cool in extremely sunny places, the duo worked on innovating a process to integrate calcium carbonate - the main component in limestone and chalk — as well as bio-compatible barium sulfate onto the polymer applied by CVD.

They explained that small particles of calcium carbonate are good at reflecting visible and near-infrared wavelengths, and barium sulfate particles reflect ultraviolet (UV) light.

Treating small squares of fabric, the researchers applied a five-micrometre-thick poly(2-hydroxyethyl acrylate) layer and repeatedly dipped the polymer-treated squares into solutions containing calcium or barium ions and solutions containing carbonate or sulfate ions.

With each dip, the crystals become larger and more uniform, and the fabric develops a chalky, matte finish.

Graduate student Patamia says that by changing the number of dipping cycles, the particles can be tuned to reach the ideal size distribution - between one and 10 micrometers in diameter - for reflecting both UV and near-infrared light.

The researchers tested the cooling abilities of treated and untreated fabrics outside in sunny weather when the temperature measured more than 90F (32.2 Celcius).

They found that air temperatures underneath the treated fabric registered 8F cooler than the ambient temperature in the middle of the afternoon.

The difference was even greater, a maximum of 1 F, between treated and untreated fabric, which heated the air underneath the sample.

Patamia said: “We see a true cooling effect.

“What is underneath the sample feels colder than standing in the shade.”

As a final evaluation of the mineral-polymer coating, the researchers simulated the friction and impact of laundry detergent in a washing machine.

They found that the coating didn’t rub away and the material retained its cooling ability.

Andrew said: “So far in our processes, we’ve been limited by the size of our laboratory equipment."

She’s now part of a start-up company that’s scaling the CVD process for bolts of fabric, which are around five feet wide and 100 yards long.

Andrew says that the venture could provide a way to translate Patamia and Yee’s innovations into pilot-scale production.

Patamia said: “What makes our technique unique is that we can do this on nearly any commercially available fabric and turn it into something that can keep people cool."

He added: “Without any power input, we’re able to reduce how hot a person feels, which could be a valuable resource where people are struggling to stay cool in extremely hot environments.”

He presented the findings at a meeting of the American Chemical Society in Denver, Colorado.

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