Recently in chemical news, Researchers at Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) have enhanced the fatigue threshold of particle-reinforced rubber through a novel multiscale approach. This innovation enables the material to withstand high loads and resist crack propagation through repeated use. The implications of this development extend beyond prolonging the lifespan of rubber products, such as tires, to potentially reducing pollution caused by the shedding of rubber particles during usage. The study, which introduces this groundbreaking approach, is detailed in the journal Nature.
Rubber Fatigue Threshold
Natural rubber latex is inherently soft and stretchy. To enhance the properties of rubber for applications like tires, hoses, and dampeners, rigid particles such as carbon black and silica are incorporated. Despite significantly improving rubber stiffness since their inception, these particles have not effectively addressed the resistance to crack growth during cyclic stretching, known as the fatigue threshold.
Remarkably, the fatigue threshold of particle-reinforced rubbers has seen minimal improvement since its initial measurement in the 1950s. Consequently, despite advancements in tire wear resistance and reduced fuel consumption, the persistence of small cracks continues to release substantial amounts of rubber particles into the environment, contributing to air pollution and environmental contamination.
The Findings
In earlier research led by Zhigang Suo, the Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials at SEAS, the team successfully increased the fatigue threshold of rubbers by elongating polymer chains and enhancing entanglements. However, the question remained: could this approach be applied to particle-reinforced rubbers?
To address this, the team introduced silica particles to their highly entangled rubber, anticipating increased stiffness without affecting the fatigue threshold, as commonly believed. Contrary to expectations, the addition of particles resulted in a surprising tenfold increase in the fatigue threshold.
Jason Steck, a former graduate student at SEAS and co-first author of the paper, expressed their surprise at this outcome, stating that they did not anticipate the particles would have such a significant impact on the fatigue threshold.
In the team’s material, polymer chains are elongated and highly entangled, while particles are clustered and covalently bonded to the polymer chains. This unique combination and breakthrough in chemical industry, deconcentrates stress around a crack over two length scales: the scale of polymer chains and the scale of particles, effectively halting crack growth in the material.
The researchers demonstrated the effectiveness of their approach by repeatedly stretching a material with a deliberately introduced crack. In their experiments, the crack showed no signs of growth, validating the success of the multiscale stress deconcentration method.
Zhigang Suo, the senior author of the study, highlighted the potential of this approach to expand the range of material properties, offering possibilities for mitigating polymer pollution and constructing high-performance soft machines.
Yakov Kutsovsky, an Expert in Residence at the Harvard Office of Technology Development and co-author of the paper, emphasized the applicability of the design principles developed in this work across various industries, including high-volume applications like tires and industrial rubber goods, as well as emerging fields such as wearable devices.
The Harvard Office of Technology Development has safeguarded the intellectual property associated with this project and is actively exploring opportunities for commercialization.
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