SINGAPORE: Imagine there’s a way to turn the plastic waste that ends up in oceans and landfills into a life-saving material, say, for making cheap fire-resistant jackets for all people.
It isn’t hard to do – at least, not any more – for a team of researchers in Singapore dreaming of reducing environmental waste and sharing their breakthrough with the world.
These scientists from the National University of Singapore and the Singapore Institute of Manufacturing Technology have converted polyethylene terephthalate (PET) bottles into a highly insulating and absorbent material called aerogel.
Aerogels, the lightest and most porous materials known to man, have existed since the 1930s – and were used to insulate the Mars Pathfinder rover in the 1990s.
But this is the first time an aerogel has been made from PET, the same plastic used for water and soft drink bottles.
And with an estimated eight million tonnes of plastic waste entering the world’s oceans each year, there is no shortage of material that could be recycled into aerogel products instead.
Their possible real-life applications include: As a lining for fire-retardant coats and carbon dioxide absorption masks that could be used during a fire; better heat and sound insulation in buildings; and cleaning oil spills.
NUS Associate Professor Hai Minh Duong, the co-leader of the research team, once used to wonder when he saw oil and plastic waste on the beach: “Can we use the rubbish on the beach to clean the oil spills?”
Fellow co-leader, Prof Nhan Phan-Thien, wanted to come up with a real product for everyone, after a lifetime of producing theories.
“We want everyone to have a (fire-resistant) jacket. For example, we all live in high-rise buildings, and the first thing is safety. And if there’s a fire … everyone can be safe,” he cites.
Now they have found a solution to these issues and more.
BETTER THAN WHAT’S OUT THERE
Over 95 per cent of an aerogel’s volume is made of air, hence the material’s high internal surface area and absorbent qualities.
Based on the team’s experiments, when their aerogel is coated with certain water-repellent chemicals, it absorbs up to seven times more oil than existing commercial sorbents can – and at a faster rate.
Owing to its insulating properties, it reduces sound more than any conventional insulation foam can, and insulates against heat many times better than fibreglass.
When coated with flame retardants, it can withstand temperatures of up to 620 degrees Celsius – seven times more fireproof than the thermal lining in conventional fire-fighting suits, but at about 10 per cent of the weight.
To explain why aerogels are given different coatings, or surface modifications, Dr Duong uses the metaphor of a video game. “That’s like an expansion pack when you buy the game,” says the 44-year-old.
“With the surface modification, you can get the wide range of applications, like if you coat the aerogels … with an amine chemical, they can absorb the toxic gases and carbon dioxide.”
The most common type of commercially available aerogel is silica aerogel, which he says sells for about S$40 per sheet (A4 size) and is used mainly in the aviation, car, gas and petroleum industries.
But his PET aerogel would cost about 50 cents to manufacture, with one recycled bottle producing one sheet.
Besides devising a more environmentally-friendly and cost-effective aerogel, his team has also shortened the production process – which typically takes up to seven days – to about eight to 10 hours instead.
It is all about the recipe used for “cooking” the materials. And Dr Duong has another metaphor handy for a complex process that starts with rendering PET down into fibres: It is like the chemistry between two people.
“It’s very similar to fibre and fibre. If you’d like (the bonding to be) strong and to hold, they need … the chemical reaction between them,” he says.
After swelling up the fibres with water and then freeze-drying them, the result is “one of the most promising materials in the 21st century”.
A SERIES OF WORLD’S FIRSTS
This is not the first time his team has created a new aerogel. Nearly three years ago, NUS announced their “world’s first” cellulose aerogel, made of paper waste.
In January, it was reported that the researchers had, in another pioneering development, turned unwanted cotton-based fabric into an even stronger aerogel.
The three aerogels have overlapping applications, although cellulose and cotton aerogels are more skin-friendly and thus could be used for personal care products like diapers, as well as in medical and battlefield settings, such as for rapid haemorrhage control.
Of the three, the PET version is the strongest and has the fastest absorption capacity. But Dr Duong’s team is not done yet with recycling environmental waste into “amazing” engineering applications.
In future, they hope to do the same with rubber waste, for example from tyres, food waste like coffee grounds and soya bean pulp, and even metal or electric waste.
People tend not to recycle now because they think waste cannot be more than low-value material, believes Dr Duong, who has been working at NUS for eight years.
“As long as they know the value of the waste, (that) they can convert it into a very high value, (then) they’d recycle,” he says.
But for now, before his team can get the world to really sit up and take notice, they must commercialise the technology for mass production.
They recently published their PET aerogel research in the scientific journal Colloids and Surfaces A, and filed for a global patent.
They had earlier licensed the cellulose aerogel technology, through the NUS Industry Liaison Office, to materials and engineering company Bronxculture, based in Singapore.
But it may still take three to five years before any commercial product is in the market, reckon Dr Duong and Prof Phan-Thien, 65.
Eager for that to happen sooner, they are in the process of starting their own company to manage their cotton and PET aerogels.
The aim is to get it up and running by the end of next year, with some 20 companies worldwide interested in partnering them already.
It is an unusual step for university professors, but on Prof Phan-Thien’s part, he is “fascinated” by this project.
“As an engineer, you need to focus on the products,” he says. “It’s good to lay your hand on something real, and this is it.”