New research sheds light on role of carbon black in strengthening rubber

Tampa, Florida – Scientists at the University of South Florida have “solved one of the oldest mysteries in materials science,” explaining how reinforced rubber works.

The breakthrough addresses a long-standing question behind rubber used in tires, automotive and aircraft components, industrial seals and medical devices, explained a 16 April statement by the university.

A team led by Professor David Simmons at USF’s College of Engineering has identified the mechanism of how adding carbon black strengthens rubber.

According to Simmons, reinforced rubber has been used for 100 years but scientists do not know how it “really works”.

Earlier theories, Simmons said, suggested that particles formed networks, acted like glue, or simply filled spaces within the rubber, but each theory failed to capture “the full picture.”

Using 1,500 molecular dynamics simulations – equivalent to around 15 years of computing time – the researchers unified the competing theories.

The key mechanism, according to Simmons, is a phenomenon called “Poisson’s ratio mismatch”, which “forces rubber to fight against its own incompressibility.”

Poisson’s ratio measures how materials change shape when stretched.

Simmons compared it to pulling back the plunger of a sealed, water-filled syringe: Water?doesn’t?compress easily, so the harder you pull the more resistance you feel.

Rubber, likewise, strongly resists changes in volume. Stretching?a normal rubber band makes it thinner as it lengthens, keeping its volume?largely unchanged.

“But when carbon black particles are added to rubber, they act like tiny supports, preventing it from thinning as much as it normally would,” explained Simmons.

When the material is stretched,?it’s?forced to increase in volume, something it strongly resists.

“In essence, the?[reinforced] rubber ‘fights against itself,’ producing a dramatic increase in stiffness and strength,” Simmons added.

The findings, he stressed, don’t?discard earlier?theories, they “unify them.”

The team found that previously proposed mechanisms – including particle networks, sticky?interactions?and space-filling effects – contribute to volume-resistance behaviour.

“Rather than competing explanations, they are pieces of a larger puzzle. By integrating them into a single framework, the researchers created the first comprehensive explanation of rubber reinforcement,” said the research lead.

The work could have direct implications for tire design, where manufacturers face the “magic triangle” of balancing fuel efficiency, traction and durability.

According to Simmons, until now, that process relied on “trial and error” to navigate the trade-offs, which is an expensive and time-consuming process.

“The struggle always is to get more than two of the three to be good,” Simmons said. “With these findings, we’re laying a new foundation for rationally designing tires.”

The impact extends beyond tires to critical infrastructure and aerospace systems, where rubber failure can have serious consequences.