McMaster University chemists claim breakthrough in rubber recycling

HAMILTON, Ontario — A team of chemists at Canada's McMaster University has discovered what the university is calling an "innovative way" to break down the rubber used in tires.

The process — described as "reductive silylation" — could lead to new recycling methods that have so far proved to be expensive, difficult and largely inefficient, McMaster said.

In a paper published by the journal Green Chemistry, Michael Brook, lead author and a professor in the department of chemistry and chemical biology at McMaster, claims the process efficiently breaks down the polymeric oils by breaking the sulfur-to-sulfur bond in tire rubber.

"The chemistry of the tire is very complex and does not lend itself to degradation — for good reason. … The properties that make tires so durable and stable on the road also make them exceptionally difficult to break down and recycle," he said.

Mr. Brook likened the structure to a piece of fishnet.

"We have found a way to cut all the horizontal lines so instead of having a net, you now have a large number of ropes, which can be isolated and reprocessed much more easily," he explained.

In a video posted on the McMaster website, Mr. Brook likened the process to "molecular scissors" that can cut through the sulfur bonds.

In the paper's abstract, the researchers claim the one-step process yielded recovery rates of 56% for "complex" mixtures of rubber crumb from ground tires to 93% for butyl rubber inner tubes.

The abstract also states the recovered polymeric oils — after the removal of inorganic materials by filtration — were cross-linked to generate new elastomers that could be reinforced with the solids recovered in the initial reduction procedure.

According to the researchers, the new method could help to eliminate and prevent the major environmental concerns and dangers posed by stockpiled tires.

While promising, researchers cautioned that the new method had some limitations as it was expensive for industrial applications.

"We're working on it, but this is the first major step. This process closes the loop on automotive rubber, allowing old tires to be converted into new products," Mr. Brook added.