USF scientists solve century-old mystery of what makes rubber stronger

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USF scientists solve century-old mystery of what makes rubber stronger

August 27, 2026

RubberWorld

Tampa, FL — Scientists at the University of South Florida say they have solved a long-standing mystery about why adding tiny particles of carbon black can transform soft rubber into a material strong enough to withstand extreme loads.

The discovery could help manufacturers design stronger, safer and longer-lasting rubber products, including tires, industrial seals and components used in aerospace and energy systems, according to the university.

The research team, led by USF College of Engineering professor David Simmons, used 1,500 molecular dynamics simulations to examine how hundreds of thousands of atoms interact inside reinforced rubber. The simulations represented about 15 years of computing time and were conducted using USF’s large computing cluster.

The findings, published in the Proceedings of the National Academy of Sciences, resolve competing theories that have surrounded rubber reinforcement for decades, the university said.

Carbon black, a form of fine carbon commonly used to reinforce rubber, has been added to rubber products for nearly a century. The practice is especially important in tire manufacturing, where reinforced rubber must withstand heat, wear and repeated stress.

Yet scientists had not reached a comprehensive explanation for why the particles make rubber dramatically stronger.

Simmons and his colleagues — postdoctoral scholar Pierre Kawak and doctoral student Harshad Bhapkar — found that the key involves a property known as Poisson’s ratio, which describes how a material changes shape when it is stretched.

Rubber naturally resists changes in volume. When an ordinary rubber band is stretched, it becomes thinner while maintaining roughly the same volume. Carbon black particles interfere with that normal thinning, effectively forcing the rubber to resist an increase in volume when stretched.

The resulting conflict causes the material to become substantially stiffer and stronger, the researchers found.

Simmons compared the effect to pulling the plunger of a sealed, water-filled syringe. Because water is difficult to compress, the resistance increases as the plunger is pulled.

The researchers call the underlying mechanism a “Poisson’s ratio mismatch.” Their findings also bring together several earlier explanations for rubber reinforcement, including theories involving particle networks, interactions between particles and the amount of space occupied by the particles.

The breakthrough could have significant implications for the tire industry, where engineers have long struggled to simultaneously maximize fuel efficiency, traction and durability — a challenge sometimes known as the “Magic Triangle.”

Manufacturers have traditionally relied heavily on testing and trial and error to balance those characteristics. A better un

*Source: Rubber World. For reference only.