According to the National University of Singapore (NUS), only 40 percent of discarded tires are recycled – the rest are either burned to generate power, or thrown in landfills. Now, however, the university has developed a method of converting old tire rubber into a high-value aerogel.
First of all, just what are aerogels? Generally speaking, they're porous, ultra-lightweight synthetic materials that are derived from a gel, although the liquid component of that gel has been replaced with a gas.
Led by Assoc. Prof. Duong Hai-Minh and Prof. Nhan Phan-Thien, an NUS team started by shredding discarded car tires into fine rubber fibers. Those fibers were then soaked in a solution consisting of water and a small amount of "eco-friendly" solvents, the latter of which caused the fibers to cross-link with one another.
That mixture was mechanically stirred for 20 minutes, forming a gel in which the linked fibers were uniformly suspended. That gel was then poured into moulds and freeze-dried at a temperature of -50 ºC (-58 ºF) for up to 12 hours.
The resulting solid rubber aerogel is said to be very lightweight, highly absorbent (it could be used to soak up oil spills), and to offer excellent thermal and acoustic insulation. Additionally, unlike traditional aerogels which tend to be brittle, this one is claimed to be highly durable. It can also be made water-resistant, if coated with a chemical known as methoxytrimethylsilane.
"The fabrication process is simple, cost-effective and eco-friendly," says Hai-Minh. "The entire production process takes between 12 to 13 hours to complete and it only cost less than S$10 [about US$7] to produce a sheet of rubber aerogel that is 1 sq m [10.8 sq ft] in size and 1 cm [0.4 in] thick. The process can also be easily scaled up for mass production. This makes rubber aerogels a commercially attractive product."
A paper on the research was recently published in the journal Colloids and Surfaces A: Physicochemical and Engineering Aspects.
Prof. Hai-Minh and colleagues, incidentally, have previously developed aerogels made from discarded plastic bottles and paper waste.
Source: NUS
