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NUS researchers use pineapple leaves to preserve fruits, remove toxic metals from wastewater

SINGAPORE — The leaves of pineapples are typically burnt after the tropical fruit is harvested, sending vast amounts of carbon into the air.

NUS researchers use pineapple leaves to preserve fruits, remove toxic metals from wastewater

The National University of Singapore team behind a biodegradable aerogels project. From left: Doctoral students Goh Xue Yang and Thai Ba Quoc, team leader Duong Hai-Minh, research engineer Nguyen Thai Thien Phuc, and undergraduate Lim Zi En.

  • An NUS research team has turned pineapple leaves into biodegradable aerogels
  • This helps cut carbon emissions, since the leaves are typically burnt after harvesting
  • Aerogels made of pineapple fibre are sturdier than those generated by other food products
  • The team plans to mass-produce the aerogels in two years

 

SINGAPORE — The leaves of pineapples are typically burnt after the tropical fruit is harvested, sending vast amounts of carbon into the air.  

Researchers at the National University of Singapore (NUS) have recently found a novel way to reuse these leaves: To preserve fruits and vegetables for at least two weeks and remove toxic metals from wastewater.

The newfangled method of turning the leaves of pineapples, commonly harvested in parts of Southeast Asia, into biodegradable aerogels (or eco-aerogels), is a project by a nine-man team from the mechanical engineering department at NUS.

Aerogels — typically made of silica, a compound of silicon and oxygen — are considered one of the lightest solids in the world, are extremely porous and low in density, and have high thermal insulative properties.

They have various uses, most commonly in heat and sound insulation. 

Turning food products into environment-friendly aerogels is not new; the NUS team has done so with soya beans, used coffee beans and other agricultural byproducts since 2016.

In this case, Associate Professor Duong Hai-Minh, the leader of the team, said that aerogels made from the fibre of pineapple leaves are sturdier and more likely to remain intact when transported. 

Moreover, pineapple harvests generate a lot of waste. This was another reason the team chose to explore ways to use pineapple leaves more sustainably. 

“For every 1kg of pineapple harvested, 3kg of waste in pineapple leaves are generated," Assoc Prof Duong told reporters at an online briefing on Tuesday (Sept 8).

Apart from getting rid of pineapple leaves by burning them, producers may also convert the leaves into low-value products such as animal feed.

Assoc Prof Duong said that the use of eco-aerogels to preserve fruits is safer than other commercial methods. Right now, fruits and vegetables are sprayed with strong oxidising agents, such as potassium permanganate, which can result in byproducts that make them unsafe for consumption.

To preserve fruits or vegetables, bars of the eco-aerogel are coated with active carbon powder and placed next to the fruits or vegetables. The aerogel then absorbs ethylene, the gas responsible for hastening the ripening of fruits and vegetables. 

This keeps them from rotting for at least two weeks, Assoc Prof Duong said.

When coated with a chemical called diethylenetriamine, eco-aerogels can also remove nickel ions in industrial wastewater at a rate four times higher than conventional treatment methods using naturally derived clay and synthetically doped graphene, a form of carbon.

At present, commercial aerogels on the market are costly, and largely used for heat and sound insulation, Assoc Prof Duong said. The manufacturing process also releases toxic levels of carbon.

By comparison, eco-aerogels are non-toxic and can be discarded safely.

They are also faster and less costly to manufacture than commercially available aerogels. For instance, it takes only half a day to produce a batch of eco-aerogels, compared with a week for commercial ones, he said.

A 1sqm sheet of eco-aerogel, measuring 1cm thick, will cost less than S$10 to produce, and can be sold for between S$30 and S$50, the researcher added. An online check by TODAY showed that a commercially manufactured blanket thermal insulation sheet made from aerogels of about the same size can retail for more than S$300.

The NUS team is in talks with two companies to commercialise its eco-aerogel. Real estate firm Mapletree intends to use it for heat and sound insulation in buildings, while the United States-based DP Aerogels is set to use the product to clear oil spills, preserve food and for other purposes.

Assoc Prof Duong said that he hopes to mass-produce the eco-aerogel in two years.

CORRECTION: An earlier version of this article stated that the researchers' method can preserve fruits and vegetables for up to two weeks. This is incorrect. The duration should be at least two weeks. We are sorry for the error. 

Related topics

NUS toxic metals food preservation pineapple leaves

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