Keeping it cool – scientists achieve room-temp tire recycling

Recycling old tires could become much more energy-efficient, plus the recycled rubber would be of higher quality

Researchers at Durham University in the United Kingdom have developed an approach to breaking down rubber in materials at room temperature. The chemical process uses catalytic disassembly, eliminating the energy-intensive methods of currently-used tire recycling methods.

In a paper published in the journal Green Chemistry, the Durham researchers explain how the process works and how it could be used to recycle vehicle tires, latex gloves, and other polymer-based items which are manufactured in the millions of tons every year. The long-chain hydrocarbon molecules and unsaturated carbons in these rubbery materials are traditionally very difficult to recycle or reprocess easily; especially vehicle tires.

The traditional method for reprocessing rubber is to drastically change the temperature of the rubber compounds to break them down, either by heating them for milling, or freezing them to fracture them. These are energy-intense and leave a crumb product which is then mixed with new elastomers to produce new material, often with a loss in hardness or malleability.

These losses mean that most recycled rubbers are not re-used for the purpose they were originally formed, but are instead recycled into other products lower down the use chain. This often means that the cost-benefit for recycling is diminished.

The Durham researchers believe that their chemical process may be used to allow the materials to be recycled back into their original use – so a recycled tire could be made into a new tire. Their cross metathesis reaction breaks down rubbery polymers into viscous liquids that can then be reformed without degradation. The process could also be used to create the crumb now commonly produced, but at much lower cost.

The process discovered uses Grubbs' catalysts to break down polybutadiene (PBd) networks at their double bonds via cross-metathesis (CM) reactions to produce readily soluble molecules. As the chains fragment, the material disintegrates into rubber crumb at room temperature. Grubbs' catalysts are easily synthesized and readily-available commercially.

The researchers also discovered that increasing temperature and reaction time improved the breakdown process, also offering a faster way to facilitate rubber compound breakdowns when producing crumb. The resulting oil is low in molecular weight and non-polymers (oligomers), both conducive to easy re-use of the polymers being recycled.

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