Researchers Produce Eco-Aerogels from Pineapple Leaves

Enzymes, vitamins, and antioxidants are abundantly present in pineapples. Such fruits are regarded as one of the most significant ones in the world.

Associate Professor Duong Hai-Minh (center) and his team from NUS Mechanical Engineering developed a technique that converts pineapple leaf fibers into ultra-light, biodegradable aerogels. Image Credit: National University of Singapore.

But the harvesting of this healthy and delicious fruit leads to a large pile of pineapple leaves waste, which is often burned or left to rot. This may, consequently, discharge greenhouse gases and toxic chemicals that can lead to adverse environmental issues.

To deal with this problem, scientists from the National University of Singapore (NUS) have developed a simple and cost-effective technique in which the fibers of pineapple leaves are used to produce biodegradable, ultra-light aerogels.

When these biodegradable aerogels are coated with certain chemicals, they can be used to store fruits and vegetables for an extended period, and to eliminate harmful metals from wastewater, among an array of other applications.

Besides these applications, the eco-aerogels can also be used again, which would further decrease waste and enhance sustainability. Moreover, the eco-aerogels can be safely discarded into the environment without causing any pollution.

At NUS Mechanical Engineering, researchers have been searching for ways to decrease waste, and thus support environmental sustainability, by upcycling different kinds of waste such as rubber, plastic, textile, and paper—into multi-functional aerogels.

The team’s new project on eco-aerogels began earlier in August 2016 and took a total of three years to deliver encouraging results.

These eco-aerogels made from pineapple leaf fibres are very versatile. They are effective as oil absorbents and for heat and sound insulation. We have also demonstrated their potential applications in food preservation and wastewater treatment. This is a big step towards sustainable agriculture and waste management, and provides an additional source of income for farmers.

Duong Hai-Minh, Study Lead and Associate Professor, National University of Singapore

The NUS researchers had also used food and other agricultural waste, such as okara, coffee grounds, and sugarcane bagasse, to produce the eco-aerogels.

Low Cost, High Value

Eco-aerogels can be created easily, and this leads to a low production cost—for example, it costs less than S$10 to create a sheet of aerogel that measures 1 m2 in area and 1 cm in thickness. When an aerogel sheet of the same size reaches the market, it can be sold at a price range of S$30 to S$50.

The fabrication procedure differs based on the type of raw material employed. The major steps involve blending/shredding, combining with water and a trace quantity of safe chemicals, stirring, aging, freezing, and finally freeze-drying.

Around 12 hours is needed on average to create aerogels from the raw materials—this is approximately 18 times faster when compared to the traditional “sol-gel” technique used for producing commercial aerogels.

Food Preservation

To make sure that eco-aerogels perform the role of food preservation, they are altered with activated carbon powder to allow them to effectively absorb ethylene gas, also called the “fruit-ripening hormone.” This gas starts the ripening process in vegetables and fruits.

This is particularly pertinent to climacteric vegetables and fruits—such as tomato, potato, papaya, mango, and banana—that continue to ripen significantly after harvest.

Vast quantities of fresh agricultural produce are discarded due to inadequate post-harvest storage and processing facilities, as well as inefficient or disrupted transportation systems. Therefore, cutting down spoilage can go a long way in reducing waste. In our lab experiments, eco-aerogels modified with activated carbon can delay the rotting process by at least 14 days.

Nhan Phan-Thien, Professor, National University of Singapore

Professor Phan-Thien, who is also a senior member of the research group, continued, “The modified eco-aerogel can absorb six times more ethylene than commercial potassium permanganate ethylene absorbents. This is also a safer method compared to the conventional use of strong oxidising agents, and more efficient than non-toxic chemical sprays, for food preservation.”

Wastewater Treatment

Eco-aerogels produced from the fibers of pineapple leaves have more robust mechanical characteristics and can also be used in wastewater treatment.

When eco-aerogels are coated with a chemical known as diethylenetriamine (DETA), they are capable of removing four times more nickel ions in industrial wastewater, when compared to traditional techniques using synthetically doped graphene and naturally derived clay.

By adopting different types of chemical coatings, the eco-aerogels can be used to extract different kinds of heavy metals from aqueous solutions.

Due to its high porosity, eco-aerogels are highly efficient in removing metal ions, even in dilute solutions where the amount of metal ions is low. The treatment process is simple, cheaper and does not generate secondary waste. Eco-aerogels can also easily desorb the metal ions and be reused several times, further reducing costs.

Duong Hai-Minh, Study Lead and Associate Professor, National University of Singapore

Future Work

The research team, comprising nine members from NUS, has now filed a patent for producing the eco-aerogels made from pineapple leaf fibers for wastewater treatment and food preservation. The team is now planning to work with an industry associate to scale up and market this new technology.

Based on their potential outcomes, the team is currently seeking to expand their studies in several major domains.

Firstly, the researchers are identifying different kinds of chemical coatings to produce eco-aerogels that exhibit high and selective adsorption of varied heavy metal ions. Secondly, they are looking at how to efficiently recover heavy metals from the eco-aerogels following wastewater treatment, in addition to reusing the eco-aerogels.

Lastly, the researchers are performing research works to create sophisticated, economical non-woven methods to fabricate eco-aerogels constantly as a roll with infinite length. Non-woven methods eliminate the need for solvents and could create eco-aerogels more quickly, using cheaper equipment and less energy. Such an approach will considerably decrease the production cost relating to eco-aerogels.

NUS Invention: Eco-aerogels made from pineapple leaf fibres

Video Credit: National University of Singapore.

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