Bridgestone Achieves Breakthrough in Room-Temperature Recycling of Vulcanized Rubber

Bridgestone and the National Institute of Advanced Industrial Science and Technology (AIST), a Japanese national research and development corporation, have jointly developed a two-stage chemical recycling process that can decompose vulcanized tire rubber under room temperature conditions.

When announcing the achievement on December 4, the two parties stated that the new technology realizes the chemical decomposition of vulcanized polyisoprene through the "rearrangement" of carbon-carbon double bonds via "metathesis reaction", followed by thermal decomposition treatment.

The products of this process include isoprene, carbon black, and BTX (benzene, toluene, xylene) which can be used as chemical raw materials.

It is reported that polyisoprene such as natural rubber can be easily decomposed through catalytic metathesis reaction, but Bridgestone pointed out that vulcanized polyisoprene rubber in waste tires is difficult to break down.

The company explained that this is because the sulfur component in vulcanized rubber inhibits the progress of the metathesis reaction.

Researchers said that selecting "suitable catalysts and solvents" for tire rubber enables the chemically decomposed of cross-linked polyisoprene under "mild conditions close to room temperature".

When explaining the process principle, Bridgestone mentioned that during the intermolecular metathesis reaction, the carbon-carbon double bonds between polyisoprene molecules undergo rearrangement.

However, the polyisoprene molecular chains generated by the reaction are of varying lengths, making it impossible to obtain only short molecular chains.

Therefore, the research team focused on achieving the chemical degradation of polyisoprene through "intermolecular metathesis between polyisoprene and low-molecular reactants containing carbon-carbon double bonds".

On the other hand, Bridgestone stated that when intramolecular metathesis reaction occurs in polyisoprene, cyclic polyisoprene is generated, thereby shortening the polyisoprene molecular chains.

In the study, the two parties confirmed through experiments that adding appropriate catalysts and solvents to vulcanized polyisoprene rubber can "significantly shorten the polyisoprene molecular chains within several hours at room temperature".

To clarify this mechanism, they conducted detailed structural analysis of the reaction products and found that the main component of the liquid polymer is a "cyclic compound with cyclic isoprene tetramer as the core".

In addition, researchers isolated and purified cyclic isoprene tetramer and conducted single-crystal X-ray structural analysis, "for the first time clarifying its molecular structure including the three-dimensional structure".

Bridgestone pointed out that when the generated liquid polymer is subjected to thermal decomposition treatment, isoprene is the main product.

AIST and Bridgestone stated that this research achievement has laid a scientific foundation for the chemical recycling of waste tires, solving the long-standing recycling problem caused by the complex sulfur cross-linking structure of vulcanized rubber.

The two parties plan to expand the technology to other rubber types such as butadiene rubber, explore application scenarios for the newly separated cyclic isoprene tetramer, and advance process scale-up research, with the goal of achieving commercial application in the 2030s.