Plastic waste frequently ends up in oceans and landfills, impacting marine life and contaminating groundwater.

Researchers from the National University of Singapore (NUS) are trying to solve the problem of plastic by converting it into something useful: Aerogels.

The resulting solidified gels, made from the bottle’s polyethylene terephthalate (PET), are lightweight, elastic, and durable.

To create the aerogels, the researcher convert the plastic waste into fibers. The fibers, after being mixed with cross-linker chemicals, are freeze-dried and cured to form the new material.

The NUS team can turn one plastic bottle into an A4-sized PET aerogel sheet.

“The fabrication technology is also easily scalable for mass production,” said Associate Professor Hai Minh Duong. “In this way, we can help cut down the harmful environmental damage caused by plastic waste.”

Duong led the research alongside Professor Nhan Phan-Thien from the Department of Mechanical Engineering at NUS Faculty of Engineering. The technology to produce PET aerogels was developed in collaboration with Dr. Xiwen Zhang from the Singapore Institute of Manufacturing Technology (SIMTech) under the Agency for Science, Technology and Research (A*STAR).

The NUS engineers were recently awarded first place in the Sustainable Technologies category of the 2018 “Create the Future” Design Contest, hosted by Tech Briefs Media Group.

In addition to being lightweight and flexible, the aerogels have strong thermal insulation and absorption capabilities. Such valuable properties could someday be used to support applications like heat and sound insulation, oil-spill cleaning, and firefighter protection.

By adding different surface treatments, the aerogel can also be customized for specific applications.

When incorporated with various methyl groups, for example, the PET aerogels can quickly absorb large amounts of oil.

“Based on our experiments, they perform up to seven times better than existing commercial sorbents, and are highly suitable for oil spill cleaning,” said Prof Nhan.

When coated with fire-retardant chemicals, a PET aerogel withstands temperatures of up to 620°C. The soft and flexible nature of the PET aerogel also provides greater comfort to the wearer, say the researchers.

When treated with an amine group, the PET aerogel swiftly picks up carbon dioxide from the environment. To illustrate a gas-mask application, the team embedded a thin layer of PET aerogel into a commercial fine particle mask to create a prototype mask that absorbs both dust particles and carbon dioxide effectively.

The NUS researchers are also exploring ways to modify the surface of the PET aerogels to better retain toxic gases such as carbon monoxide.

Prof. Duong spoke with Tech Briefs about the plastic problem – and the many aerogel possibilities that can emerge from it.

Tech Briefs: How did this idea come about?

Hai Minh Duong, Department of Mechanical Engineering, National University of Singapore (NUS) Faculty of Engineering: Plastic bottle waste is one of the most common types of plastic waste, and it has detrimental effects on the environment. I would like to use environmental waste to solve environmental problems.

Currently, the recycling of plastic waste is mainly for low-value applications and simple uses, so people tend not to appreciate the value of the raw materials they throw away. Hence, this inspired me to want to develop novel, high-value aerogel materials.

Additionally, there have been several high-rise building fire accidents in Vietnam where many people died. I wondered if there was any way to help them to escape safely.

Sound and air pollution are also critical problems in China and Vietnam which I hope to address as well.

Tech Briefs: Is the conversion process a complex one? Can it be easily implemented? How does it work?

Prof. Duong: The process to produce PET aerogels can be easily implemented, and is highly scalable and cost-effective. We only need the initial chemicals, sonicator, and the freeze-drying equipment for the whole process.

Hai Minh Duong, Department of Mechanical Engineering, National University of Singapore (NUS) Faculty of Engineering, Professor Nhan Phan-Thien, and the team at the National University of Singapore hold up demonstrations of aerogel products made from plastic waste. Khac Duyen Le, Research Engineer, Department of Mechanical Engineering, NUS Faculty of Engineering, Leung Hoe Inn, Ryan, final-year undergraduate student, Department of Mechanical Engineering, NUS Faculty of Engineering, Professor Nhan Phan-Thien, Department of Mechanical Engineering, NUS Faculty of Engineering, Associate Professor Hai Minh Duong, Department of Mechanical Engineering, NUS Faculty of Engineering, Dr Xiwen Zhang, Singapore Institute of Manufacturing Technology, Agency for Science, Technology and Research
The NUS team demonstrates how their aerogels can be used in a variety of applications, including heat insulation and carbon dioxide absorption. (Image Credit: NUS). From left: Research engineer Khac Duyen Le, Final-year undergrad Leung Hoe Inn, Professor Nhan Phan-Thien, Associate Professor Hai Minh Duong, and Dr Xiwen Zhang from the Singapore Institute of Manufacturing Technology, Agency for Science, Technology and Research.
Tech Briefs: What are the kinds of applications that are possible with this kind of aerogel?

Prof. Duong: The heat insulation property of the PET aerogels can be applied to various consumer products, such as cooler bags to keep food items fresh. I also foresee tremendous potential for other high-value applications like pipeline insulation and transportation of liquefied natural gas, which needs to be stored at a low temperature.

The PET aerogels can also act as a lightweight lining for firefighter coats and carbon dioxide absorption masks employed during fire rescue operations and fire escape. The masks can additionally be used in countries where air pollution and carbon emissions are of great concern.

The aerogels also support oil spill cleaning, as well as heat and sound insulation in buildings.

Tech Briefs: What kind of impact can this process have on the environment?

Prof. Duong: Globally, the annual consumption of plastic bottles has been rising steadily, and it is expected to exceed half a trillion tons per year by 2021. In the U.S., 1500 plastic water bottles are consumed every second, causing major problems for humans, the environment, and the animals on our planet. The UK is also facing a similar problem.

Plastic bottles are made from polyethylene terephthalate (PET), and most of them are not recycled. They either end up lying stagnant in landfills, leaching dangerous chemicals into the ground, or they infiltrate our streets as litter.

We hope to solve the global environmental problem by letting people know how raw materials like plastic waste can be turned into high-value materials for different applications, and encourage the idea of recycling them.

What do you think? Will plastic-bottle aerogels help to solve environmental problems? Share your comments and questions below.