Eco-Friendly Technique Converts Paper Waste into Useful Aerogels

A group of researchers from the National University of Singapore’s Faculty of Engineering have been the first to find a method to convert paper waste into green cellulose aerogels. These aerogels are water repellent, ultralight, non-toxic, flexible, and very strong, making them suitable for applications like packaging, heat insulation, and oil spill cleaning.

Aerogels can also be effectively used as smart materials for a number of biomedical applications, and as a coating material for drug delivery. The research group was headed by Assistant Professor Duong Hai Minh from the Department of Mechanical Engineering.

Aerogels, which are among the lightest solid materials known to man, are one of the finest insulation materials available. Traditional aerogels are mainly made of silica, which is not environmentally-friendly. In contrast, cellulose is low cost and makes up 75 to 85 per cent of recycled paper. Our team developed a simple, cost-effective and fast method of converting paper waste into aerogels. In addition to low thermal conductivity, these novel aerogels have several unique features, one of which is super high oil absorption capacity - it is up to four times higher than commercial sorbents available in the market. We are very excited about the potential applications of this new material.

Professor Duong Hai Minh, Department of Mechanical Engineering, NUS

Reduce environmental problems by recycling paper waste

On a global level, the production of paper is expected to rise to 500 million by 2020. The amount of waste generated because of paper will also increase annually and it becomes difficult to dispose of. This increase in paper-related waste production leads to forest destruction and also pollutes the environment. The environment can be conserved by creating useful products through conversion, or recycling of paper waste.
A more eco-friendly technique has been developed by the NUS team for the conversion of paper waste into aerogels.

Our fabrication process uses 70 per cent less energy, produces fewer polluting emissions into the air and water, as well as uses less dioxins in the chlorine bleaching process. It is also faster – the entire process only takes three days.

Professor Duong Hai Minh, Department of Mechanical Engineering, NUS

Four times more effective than commercial oil sorbents

The unique cellulose aerogels possess extremely high oil absorption capacity and are water repellant. The aerogels are coated with Trimethoxy-methylsilane (MTMS), and can absorb oil that is 90 times of their dry weight. Due to this property,  the aerogels are considered to be four times more effective than other oil sorbents that are commercially available. It is possible to recover more than 99% of the crude oil by squeezing the aerogels.

Oil spills are serious disasters that threaten marine ecosystems. Sorption has been considered one of the most effective ways to clean oil spills. Polypropylene (PP)-based absorbents are widely used for oil absorption but they are non-biodegradable, and their absorption capabilities are both low and slow. Our novel cellulose aerogels therefore serve as an attractive alternative to current methods of oil spill cleaning, which has a potential market size of US$143.5 billion.

Professor Duong Hai Minh, Department of Mechanical Engineering, NUS

Super heat insulation materials

The unique cellulose aerogels are also used as insulation materials for buildings.

It is observed that buildings in Singapore, consume about two-thirds of energy in air-conditioning, and about 25%-30% of heat losses in buildings are from doors, windows, roofs, and basements. As a result, there is a high demand in the market for environment-friendly sorbents, which possess water repellant properties and great absorbing capacity. The sorbents also provide effective heat insulation, and are less expensive to install. It is globally observed that, thermal insulation of buildings has a potential market of US$3.3 billion.

As a heat insulation material, our novel cellulose aerogels offer a few added advantages. Their water repellent property allows them to be adaptable to both dry and rainy weather and their structure remains stable for about six months in tropical climate. Being extremely strong, they increase building strength. In addition, these aerogels are lightweight and slim, resulting in slimmer walls, thus increasing building space.

Professor Duong Hai Minh, Department of Mechanical Engineering, NUS

Potential applications aplenty

The applications of these aerogels could be utilized in the packaging industry. The use of plastic-based packaging materials, like the bubble wrap, can now be replaced with advanced cellulose aerogel nanosheets or eco-friendly biodegradable aerogel-based foams.

The aerogels have high porosity and high surface area, and can be used as smart materials or coating materials in drug delivery.

The researchers have discovered a technique to expand the weight capacity of the aerogels. In this method, fibers of the cellulose aerogels are infused with a solution of metallic nanoparticles. This is followed by hammering the cellulose aerogels to make them flat, in order to remove a huge amount the air, and a magnetic thin film is obtained. This thin film has a weight capacity of more than 28 tonnes per square centimeter.

The hydrophilic property of MTMS-uncoated cellulose aerogels allows them to absorb and retain high volumes of polar fluids like alcohol and water. This property enables the MTMS-uncoated cellulose aerogels to be used in products like sanitary napkins and baby diapers.

Additionally, cellulose aerogels in the compressed form can be injected into the wound cavity to plug life-threatening wounds, like stabbing lesion and gunshot. The sponges present in the aerogel expand inside the cavity, and create pressure that is sufficient to block life-threatening haemorrhage and bleeding in 20 seconds or less. Survival rates can be greatly enhanced because of this incredible speed found in the cellulose aerogels.

From idea to market

The team have registered a patent for this new invention in Southeast Asia, India, China, and the U.S. For commercialization, this new technology has been licensed by the NUS Industry Liaison Office, which is part of NUS Enterprise, to Bronxculture Pte Ltd in November 2015. Bronxculture plans to manufacture the cellulose aerogels and then expand its applications in three areas, such as, oil absorption materials, insulating materials for packaging boxes, and insulating layer for winter garment.

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