Old tires are known to have a huge negative environmental impact if disposed of carelessly. It is often that these end up in landfills, or get burnt, emitting alarming amounts of hydrogen chloride, carbon monoxide and hexavalent chromium- all toxic gasses contributing to climate change.
Current methods for recycling tires are energy intensive. They require extreme temperatures (very high or very low) to change the compounds in the tires. These are broken down by milling or fracturing, depending on whether they are heated or frozen. The byproducts are then mixed with other materials to produce a new material, which is less hard and less flexible. Consequently, the benefits from such process in terms of costs are not too high.
British researchers from University of Durham, the UK, have found a way to efficiently recycle old tires. Not only that, they actually found a way to turn the old tires into new ones. The process is chemical, and it uses catalytic disassembly instead of energy consuming temperature changing procedures.
In more detail, using a cross metathesis reaction, the rubbery polymers are broken down to produce viscous liquids. These can then be reused and reshaped without experiencing any degradation in quality. This essentially results in great reductions of costs.
The catalysts used to break down the polybutadiene (PBd) networks are Grubbs catalysts. These are easily synthesized and are readily available for commercial purchase. The way they act is by attaching to the PBd at their double bond via the so called cross-metathesis reactions. The final products are essentially soluble molecules. At room temperature, the chains fragment, and the material disintegrates into rubber crumb.
The method is not only applicable to rubber tires. It can also be successfully used to recycle all rubber materials and polymer-based items, including latex. The team also found that if the temperatures are increased slightly and the breaking down process is optimized, the rubber compounds produce crumb faster. There is also residual oil, which has very low molecular weight and non-polymers, enabling easy reuse of the polymers.
The study is published in the latest issue of Green Chemistry.
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