Weaker rubber crosslinks 'could reduce tire microplastics'

Durham, North Carolina – A research team in the US has developed a durable rubber material that can potentially reduce particle emissions from tires.

The researchers from Duke University in Durham and MIT carried out a study on the chemical reactions within elastomers, with a focus on weaker molecular bonds.

Working with polyacrylate elastomers, the team replaced the cross-links with ones that were five times weaker, using ring-shaped cyclobutane which breaks apart under strain.

Everything else being equal, said Duke chemistry professor Stephen Craig: "You’d think that linkers that break more easily should produce materials that are easier to tear.”

Instead, “surprisingly, the overall network got much stronger as opposed to weaker,” according to Craig.

In mechanical tests, the researchers loaded thin sheets of each material into a machine that measures the force it takes to rip a sample.

Both elastomer samples were similar in terms of stiffness and elasticity, but the one made with weak cross-linkers was up to nine times more difficult to tear than the one cross-linked with stronger bonds.

“The toughness enhancement comes without any other significant change in physical properties, at least that we can measure,” Craig said.

The feature, he went on to say, is brought about through the replacement of only a small fraction of the overall material.

Explaining the process, first author Shu Wang said tearing in a polymer material is essentially a chemical reaction.

Typically, the polymer strands that span the leading edge of the tear must break for the crack to spread.

But in their design the weak cross-links break first, leaving the main polymer thread 'uncinched' but otherwise intact.

“This helps the material resist breaking down further, even once small nicks and blemishes start to form,” he said.

The team has filed a patent on the approach with “much work to be done” to use the insights to develop tougher synthetic rubber, for tires for instance.

Citing previous studies, Craig said it is estimated that, each year, tires release some 6 million tonnes of dust and debris.

These emissions, he added, account for as much as 10% of the microplastics in oceans, and 3-7% of the particulate matter in the air.

“That’s just from tire tread wearing down on roads,” Craig said.

“If you could reduce that by even 10%, that's still 600,000 tonnes of microplastics you'd be keeping out of the environment.”