A way to dissolve the rubber used in car tires and recover the polymers to keep this typically single-use item out of landfill

About

Background

This technology addresses the enormous environmental burden posed by tires, approximately 3 billion of which were manufactured and purchased worldwide in 2019. Most of those will end up in massive landfills or storage facilities, ultimately leaching contaminants into the ecosystem.

Tires are a typical example of a product prepared for a single use from a non-renewable resource. While some are used as fuel in the cement industry or broken down into crumbs to use as fillers in asphalt, cement or artificial turf, there is no convenient method for recovering the petroleum-based polymers from which they are made so they cannot be easily reused, effectively repurposed, or recycled.

McMaster researchers describe a process to efficiently break down the polymeric oils by breaking the sulfur-to-sulfur bond.



Technology Overview

A team of chemists at McMaster has discovered an innovative way to break down and dissolve the rubber used in automobile tires, a process which could lead to new recycling methods that have so far proven to be expensive, difficult and largely inefficient.

This efficient and mild process uses silicone chemistry to break the sulfur-to-sulfur bonds that hold tires together. The silicones selectively cut the sulfur-sulfur connections, leaving only organic chains that can be easily isolated and reused to create new products. This process, originally designed to make new silicones using very small quantities of a catalyst, has been repurposed to address the sustainability of petroleum-based tires (Figure 1).

The chemical process first involves cutting tires into sections and then forming powdered crumb from them, steps that are currently used in commercial tire recovery plants. Then, a mild, rapid reaction produced by heating this material with specific silicones at 100C for 45 minutes converts about 90 per cent of the available organic materials into a readily processed pale yellow oil. The remaining substances — such as inorganic carbon, silica, metal and polyester cord fibres — are readily removed by filtration. The oils recovered from used tires are very similar in constitution to the virgin polymers initially used to make new tires.


Stage of Development

Recovered polymers were converted back into new rubbers, with the tire of the model toy car. The next steps will be to better establish the range of products that can be made from the recovered polymers and reduce the quantity of catalyst needed to improve the economics of the process.


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Applications

This new method could help to eliminate and prevent the major environmental concerns and dangers posed by stockpiled tires. The overall process offers an opportunity to close the loop on automobile tires, as the rubber can be efficiently degraded and then reused to make other useful materials. It provides a new strategy to re-purpose the valuable materials in used tires and simultaneously address a perplexing environmental problem.

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