Cellulose film could help cool cars and homes without electricity

Alfonso Maruccia

Posts: 968   +293
Staff
Why it matters: Summer is coming, and A/C units will soon start humming to try and keep our homes and offices a bit cooler than the sunny hellscape waiting for us outside. But air conditioning comes with an enormous waste of electric energy, which in turns brings more greenhouse gases to an already boiling atmosphere.

As global warming is a phenomenon that sane-mind people can feel on their own skin, we are in desperate need for alternative cooling technologies that won't add any more harmful emissions to our overheating planet. A potential solution to this hot issue comes from passive daytime radiative cooling (PDRC), which is the ability of a surface to emit its own heat into space without it being absorbed by the air or atmosphere.

PDRC materials can become several degrees colder than the air around them, and with no need for electrical power or other external energy sources. Passive cooling surfaces could be embedded in buildings or cars, promoting a substantial cooling effect without using air conditioning units or other active, power-intensive methods.

Researchers from Cambridge University, UK, are working on a novel cellulose film with PDRC properties, a plant-based, two-layered material that gets cooler when exposed to direct sunlight. The film can also be treated to provide bright, iridescent colors, and a variety of textures which would help with integrating the material in home furniture or automotive applications.

The UK scientists presented their results during the ACS Spring 2023 hybrid meeting, explaining how cellulose is one of the few naturally occurring compounds that can promote a PDRC effect. Adding a color pigment to a material is detrimental to the aforementioned PDRC effect, as pigments absorb specific wavelengths of visible light and only reflect the color(s) we see. The absorbed electromagnetic radiation is then turned into heat.

To solve the heating issue, the researchers focused on natural structures that can show a colorful effect that doesn't require the presence of a pigment. Something like the prismatic effect seen on a soap bubble, which is the result of the way visible light interacts with the bubble's surface at the microscopic level.

The effect is known as structural color, and Ph. D. Silvia Vignolini (the project's principal investigator) found that plant-derived cellulose nanocrystals (CNCs) can be employed to produce iridescent, colorful films with no addition of external color pigments.

Vignolini's team added a second layer to the iridescent, CNC-based film, using a white-colored material made from ethyl cellulose and finally creating a colorful, bi-layered film with PDRC properties. When placed under direct sunlight, the film was nearly 7F cooler than the surrounding air. Sticking together the two cellulose layers was the most difficult part of the research, the UK scientists said, but the final result can be adapted to a standard manufacturing line for mass production.

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The temperature cooling is ok, but how about the HUMIDITY.
Sometimes, where I live, the temperature can be in the upper 70's, but the humidity level
in the 60%+ range, making it very sticky.
AC units not only cool the air, but remove the humidity.
Sometimes, the drain hoses look like a garden hose evacuating the water.
 
So, if you live in Riad (or Riyadh) and outside temperature is 52 °C (~126 °F), you put this special t-shirt on and your local temp drops to chilly 48 °C (~118 °F)?
 
The temperature cooling is ok, but how about the HUMIDITY.
Sometimes, where I live, the temperature can be in the upper 70's, but the humidity level
in the 60%+ range, making it very sticky.
AC units not only cool the air, but remove the humidity.
Sometimes, the drain hoses look like a garden hose evacuating the water.

70°? That temperature would result in instant death for any human being. When it hits 40-42° here, many more sensitive people already start to faint. lol
 
70°? That temperature would result in instant death for any human being. When it hits 40-42° here, many more sensitive people already start to faint. lol

70s Fahrenheit, which is relatively low, but the higher humidity makes it feel very uncomfortable since you feel like you're constantly damp and your body can't cool as effectively.

I grew up in 100+ (37+) summers with 100% humidity. That's when it gets really fun.
 
So, if you live in Riad (or Riyadh) and outside temperature is 52 °C (~126 °F), you put this special t-shirt on and your local temp drops to chilly 48 °C (~118 °F)?
Yes, but if you stuck it on a building you'd have that that 4 °C less cooling requirement, times however many buildings and cars. To be honest I have no idea if it'd be worth the trouble of installing it when it's that hot, but it would cut the cooling requirements (and power bill) by about 15%. If it's 90F out and you're cooling to like 75F (33C to 24C), then it's doing half the cooling for you (I don't know if it'd cut the POWER use in half since there's humidity to worry about too, but that's still going to save a lot).

I guess my question (as a few have brought up) is if it works if it's humid. To be honest, I *thought* plants just used evaporative cooling. Having a pre-installed swamp cooler on your building or car could be great in many climates, but here when it's 90-100 (32-38C) it's also usually 70-90%+ humidity so a swamp cooler won't do jack. That said, it's a sheet of cellulose, not a plant, so it does NOT sound like it's evaporative cooling, I guess it actually is some property of the cellulose. Cool! (Pun intended)
 
Yes, but if you stuck it on a building you'd have that that 4 °C less cooling requirement, times however many buildings and cars. To be honest I have no idea if it'd be worth the trouble of installing it when it's that hot, but it would cut the cooling requirements (and power bill) by about 15%. If it's 90F out and you're cooling to like 75F (33C to 24C), then it's doing half the cooling for you (I don't know if it'd cut the POWER use in half since there's humidity to worry about too, but that's still going to save a lot).

I guess my question (as a few have brought up) is if it works if it's humid. To be honest, I *thought* plants just used evaporative cooling. Having a pre-installed swamp cooler on your building or car could be great in many climates, but here when it's 90-100 (32-38C) it's also usually 70-90%+ humidity so a swamp cooler won't do jack. That said, it's a sheet of cellulose, not a plant, so it does NOT sound like it's evaporative cooling, I guess it actually is some property of the cellulose. Cool! (Pun intended)

We better let them develop the idea further, if they reach a difference of 8 degrees centigrade, that would be worth trying.
 
Durability will be an issue even if this tech is functional. Cellulose, the main component in wood tends to break down quickly.
 
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