Technological breakthroughs

Compiled by Bao Hien

Researchers at Harvard University in the US have found a way to blend silica into natural rubber without breaking the polymer chains, making the material roughly 10 times more resistant to cracking while keeping it stiff.

The work was published in the journal PNAS on March 23 by the group of Professor Zhigang Suo, with Matthew Wei Ming Tan as first author. The university publicized the findings at the end of April.

Natural rubber, combined with silica or carbon black, is the main material in truck, bus and aircraft tires. According to the team, the weakness lies in the familiar manufacturing step. Dry rubber is kneaded with filler and additives in high-intensity equipment. The strong shear spreads the filler evenly but also breaks the long polymer chains, the part that gives rubber its elasticity. Shorter chains leave the material less elastic, less tolerant of cold and more prone to cracking.

Dissolve first, mix later

To avoid this, the team reversed the sequence. Natural rubber latex consists of tiny spheres suspended in water, and silica particles cannot enter them. The scientists used toluene, a common industrial solvent whose polarity matches that of rubber, to dissolve the chains out of the latex particles, producing a uniform solution of individual chains.

Silica was then stirred into the solution at low intensity, enough to disperse the particles without cutting the chains. The mixture was dried into a solid, molded and cured. In the final step the chains are only sparsely cross-linked to one another and to the silica particles.

Tougher, yet still stiff

Measurements show that toughness, the energy the material absorbs before a crack starts to grow, rose from about 2 to 44 kJ/m². The team describes the increase as about an order of magnitude, or roughly 10 times. The modulus, a measure of stiffness, reached about 19 MPa, a high level. The two properties usually trade off: the stiffer a material, the more easily it cracks.

The team says the approach is not limited to one filler. It has been tried with several grades of silica and with carbon black.

First target: truck, bus and aircraft tires

The researchers say the material is aimed at tires that already use a lot of natural rubber. In the longer term, passenger-car tires made largely from bio-based rubber are feasible if cost and supply can be solved. Industrial belts, seals and soft robotic parts that must flex repeatedly are other potential uses.

According to co-author Yakov Kutsovsky, the need grows as electric vehicles spread. “Electric cars are heavier than ordinary cars, and larger loads on the car is going to make the tires wear out faster,” he said. This is his opinion, not a result of the study.

Much work remains

The study has so far measured fracture and fatigue resistance, not abrasion or tire lifetime directly. High crack resistance generally goes together with better wear resistance, but that is an inference, not something verified. No tests on actual tires have been reported, and cost and supply at industrial scale remain open questions.

Toluene is volatile and toxic. The team says it can be run in a closed, recovered loop, but the sources do not describe the energy use or environmental impact of the dissolving and drying steps. The silica content, mixing time and curing conditions were also not given in the reports.

It should be noted that the reports cross-checked here all stem from the same university press release, so they agree on the content but are not independent verification.

References
1. Tan, M. W. M., Nian, G., Chen, Z., Bao, X., Suo, Z., & Kutsovsky, Y. (2026). Amplifying toughness in silica-reinforced natural rubber by preserving long chains. Proceedings of the National Academy of Sciences. https://www.pnas.org/doi/10.1073/pnas.2530834123
2. Harvard John A. Paulson School of Engineering and Applied Sciences. (2026, April 27). Toward tougher, longer-lasting, more sustainable tires. https://seas.harvard.edu/news/tougher-longer-lasting-more-sustainable-tires