Rubber tyres upcycled into multi-use aerogels

Researchers have converted waste rubber tyres into aerogels with a wide range of applications, an advance claimed to be a first by the team at the National University of Singapore.

The new rubber aerogels are claimed to be extremely light, highly absorbent, very durable, and efficient at trapping heat and sound. A patent has been filed for the novel technology, which the team said promotes a wider use of scrap tyres and offers an eco-friendly way to recycle used rubber. The team’s findings have been detailed in Colloids and Surfaces A: Physicochemical and Engineering Aspects. 

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Around one billion highly durable and non-biodegradable tyres are scrapped globally per year, with 40 per cent of them recycled into low-value-added products. A further 49 per cent are incinerated to generate energy, and at least 11 per cent end up in landfills.

“The rate of recycling worldwide remains low because processing used rubber is costly and energy-intensive, coupled with a lack of monetary incentive. Our team has decided to focus on creating rubber aerogels from used rubber tyres because they are a cheap and abundant source of raw materials. By converting waste rubber tyres into high-value aerogels, we could enhance the monetary incentive for recycling rubber and in turn, cut down rubber waste,” said Associate Professor Duong Hai-Minh, who led the research team from the Department of Mechanical Engineering at NUS Faculty of Engineering.

To create the rubber aerogels, recycled car tyre fibres are first blended into finer fibres. According to NUS, these fine rubber fibres are then soaked in water and a small amount of chemical cross-linkers. The mixture of rubber fibres and eco-friendly solvents is then dispersed uniformly using a stirrer for 20 minutes. The uniform suspension gel is then freeze-dried at minus 50^oC for up to 12 hours to produce rubber aerogels.

In a statement, Assoc Prof Duong said, “The fabrication process is simple, cost-effective and eco-friendly. The entire production process takes between 12 to 13 hours to complete and it only costs less than US$7 to produce a sheet of rubber aerogel that is 1m² in size and 1cm thick. The process can also be easily scaled up for mass production. This makes rubber aerogels a commercially attractive product.”

The aerogels are said to be extremely light and stiffer than commercial foam and 27 per cent more effective than the commercial foam sound absorber with the same thickness. They are also two times more absorbent than conventional absorbents such as the polypropylene mat, and a piece 2.54 cm thick is claimed to have a heat transfer limit that is equivalent to 25 standard glass windowpanes. When coated with methoxytrimethylsilane, the rubber aerogels become extremely water-repellent and they can be used to prevent moisture from corroding or damaging insulation equipment.

“Potential markets of aerogels are huge. For example, vehicle noise and thermal comfort are vital in vehicle designs – the global automotive heat and sound insulation solution market are expected to reach US$3.2bn by 2022. In addition, the global oil spill management market is expected to reach US$182.7bn by 2025,” said Professor Nhan Phan-Thien, a senior member of the research team.