It’s now almost instinctive for many of us to recycle our paper, but a glut of paper waste still makes recycling a challenging economic proposition. Now an additional recycled paper use may help with the issue. A research team from the National University of Singapore’s (NUS) Faculty of Engineering has successfully converted paper waste into green cellulose aerogels that are non-toxic, ultralight, flexible, extremely strong and water repellent. This novel material is ideal for applications such as oil spill cleaning, heat insulation as well as packaging, and it can potentially be used as coating materials for drug delivery and as smart materials for various biomedical applications. The research team was led 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,” said Duong.
The NUS team has also developed a more eco-friendly process to convert paper waste into aerogels.
Duong said that their 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.
The novel cellulose aerogels developed by the NUS team boast super high oil absorption capacity. Coated with Trimethoxy-methylsilane (MTMS), the aerogels are water repellent and are capable of absorbing oil (excluding water) up to 90 times their dry weight, making them up to four times more effective than commercial oil sorbents. Furthermore, they can be squeezed to recover over 99 per cent of the crude oil absorbed.
According to Duong, 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. The novel cellulose aerogels serve as an attractive alternative to current methods of oil spill cleaning, which has a potential market size of US$143.5 billion.
Another important application of the novel cellulose aerogels is to serve as insulation materials for buildings.
In Singapore, air-conditioning of buildings take up about two-thirds of the energy consumption in buildings. About 25 to 50 per cent of heat losses are from windows, doors, basement and roof of the buildings. These have resulted in a high market demand for eco-friendly sorbents which have greater absorbency and water repellent properties, as well as effective heat insulation materials that are less costly to install. Thermal insulation of buildings is estimated to have a potential market of US$3.3 billion globally.
According to Duong, as a heat insulation material, the 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. Additonally, these aerogels are lightweight and slim, resulting in slimmer walls, thus increasing building space.
The aerogels could also signal a change in the packing industry. Plastic-based packing materials such as the bubble wrap could be replaced with biodegradable aerogel-based foam or advanced cellulose aerogel nanosheets, which are environmentally-friendly.
With high surface area and high porosity, the biodegradable aerogels could also be used as coating materials in drug delivery or as smart materials.
The NUS team also discovered a way of expanding the weight capacity of the cellulose aerogels. This is achieved by infusing the fibres of the cellulose aerogels with a solution of metallic nanoparticles. The cellulose aerogels are then hammered flat to remove most of the air, resulting in a magnetic thin film that has a weight capacity of over 28 tonnes per square centimetre.
MTMS-uncoated cellulose aerogels are hydrophilic — they can also absorb and retain huge volumes of polar fluids such as water and alcohol, making them appropriate for possible use in products such as baby diapers and sanitary napkins.
Duong mentions that compressed cellulose aerogels can be used to plug life-threatening wounds such as a gunshot or stabbing lesion by injecting them into the wound cavity. The sponges expand inside the cavity, creating pressure that can block bleeding and life-threatening haemorrhages in 20 seconds or less. This speed of blockage could greatly enhance wound-related survival rates.
The team has filed a patent for their invention in USA, China, India and Southeast Asia. The technology has been licensed by the NUS Industry Liaison Office to the Bronxculture Pte Ltd inNovember 2015 for commercialization. Bronxculture intends to manufacture the cellulose aerogels and further expand its applications in three areas, namely, insulating materials for packaging boxes, insulating layer for winter garment and oil absorption materials.