Environment

PET Bottles Have New Value as Aerogels Which Absorb CO2 and Withstand High Heat

Single-use plastic bottles made of polyethylene terephthalate (PET) have been of little use for recyclers, but all that could change thanks to a unique innovation created at the National University of Singapore.

Bottom of a PET (polyethylene terephthalate) single-use plastic bottle.

The PET bottles have the dual distinction of being non-biodegradable and up until now had almost no value as raw material for something else.

What the researchers at the National University of Singapore discovered was a way to convert the raw PET from bottles into a unique kind of aerogel.

Aerogels are materials with almost 100% air embedded inside the materials, in air pockets. With so much of the items being gas, not solid, they feel virtually weightless. For commercial industry, they are often used for insulation of one sort or another.

When PET is converted into an aerogel according to the new process, each bottle yields an aerogel sheet about the size of a single letter-sized piece of paper.

The new aerogels the researchers made from PET have two potential major uses. When protected with fire retardants (to keep them from burning), the aerogels can stay in their original shapes at temperatures up to 620 degrees Celsius (1148 degrees Fahrenheit). That’s over 7X what conventional thermal linings used in firefighter coats can handle. Further, being an aerogel, it weighs less than 1/10th what the coats normally weigh. They are also soft to the touch and highly flexible.

The PET-based aerogels also absorb high amounts of carbon dioxide and carbon monoxide. They therefore have major applications in inexpensive and lightweight masks to protect a user from areas with high air pollution.

As Hai Minh Duong, an associate professor connected with the PET-aerogel innovation said, “Masks lined with amine-reinforced PET aerogels can also benefit people living in countries such as China, where air pollution and carbon emission are major concerns. Such masks can be easily produced, and can also potentially be made reusable.”

Noting that the material does absorb carbon dioxide, some have speculated that the material might be usable for mass carbon-capture to help combat global warming. No experiments on that kind have begun yet, and the scientists are cautious about over-promising in that application.

Other places the new PET aerogel may be of use take advantage of the material’s other important properties in dampening sound and helping with thermal insulation. They could be used inside walls as a thermal insulator, and to prevent sound from traveling through the walls.

According to Associate Professor Duong, the material also appears to have an important application in mass-cleanup applications. “Based on our experiments,” he said, “they perform up to seven times better than existing commercial sorbents, and are highly suitable for oil spill cleaning.”

The next step the researchers are working on is to select the most promising near-term commercial applications for the material – and then begin making prototypes for funding consideration.