Dr Shigetaka Hayano | The Rubber Revolution: Cracking the Code for Tire Recycling!

Traditionally, rubber waste was nearly impossible to recycle due to crosslinked sulphur bonds. But a team of researchers led by Dr Shigetaka Hayano from Zeon Corporation, in Japan, have achieved a groundbreaking feat in rubber recycling. Using mild conditions for the reaction, scientists have overcome the unfavourable cross-linked structure and have achieved recovery of rubber’s original monomers. This process restores cyclopentene monomers with 90% efficiency, allowing old tires and industrial rubber waste to be chemically recycled into high quality materials. If scaled up, this innovation could revolutionise waste management, reduce environmental pollution, and enable a circular economy for rubber production.

Revolutionary Rubber Recycling: Unlocking a Circular Economy

Rubber is everywhere—essential in car tires, medical devices, industrial machinery, and household goods. Yet, its biggest flaw is its resistance to recycling. Unlike plastic, which melts and reshapes, rubber’s vulcanisation locks its structure in place, making it nearly indestructible. Millions of tons of rubber waste accumulate each year, with few options beyond burning, shredding, or dumping.

That might be about to change.

In Japan, Dr Hayano and colleagues have just achieved the impossible – or at least, what the industry once thought was impossible. They have reverse engineered vulcanised rubber, breaking it down into its original building blocks. Even better? They did it using mild heat, a clever catalyst, and smart chemistry: no extreme conditions, no blast furnaces, no harmful by-products.

This groundbreaking discovery means old tires and industrial rubber waste could soon be fully recycled, and not into low value scraps, but back into high quality raw materials for new rubber products. It’s the kind of scientific leap that doesn’t just improve a process; it could transform industries and reshape environmental policies around the world.

Why Rubber Recycling Has Always Been So Difficult

Most plastics can be remelted and reshaped because their polymer chains stay intact. Rubber, however, undergoes vulcanisation, where sulphur crosslinks its molecules, locking the structure. This makes rubber strong, heat-resistant, and durable, ideal for uses like tires and seals. But once vulcanised, rubber can’t be remelted or remoulded, making it hard to recycle traditionally. This toughness is exactly why rubber is used in high impact environments, from tires to industrial gaskets. But once rubber is vulcanised, it can’t be melted or reshaped – it’s chemically stuck.

As a result, recycling rubber has always been a challenge. Currently, old rubber products are mostly:

• Burned for fuel, releasing harmful emissions.
• Shredded for filler, like in playgrounds.
• Dumped in landfills, where they don’t decompose.

Millions of tons of rubber waste are generated yearly, with little chance of reuse. Scientists have long sought a way to reverse vulcanisation, but until recently, none had done so efficiently.

The Molecule That Made It Possible: Cyclopentene

At the core of this breakthrough is cyclopentene, a simple hydrocarbon molecule. Through ring-opening metathesis polymerisation (ROMP), it forms rubber polymers; under the right conditions, the process can reverse, restoring the original monomer. It’s like hitting ‘Undo’ at the molecular level.

While this reaction worked in laboratories, applying it to tough, vulcanised rubber that often contains additives (such as carbon black) was a challenge – one that scientists at Zeon Corporation in Japan set out to overcome.

Turning Tires Back into Monomers

In their groundbreaking study, the Zeon team tested three types of cyclopentene rubber that can be applied for high performance tires of passenger cars/large vehicles, special sealants, rubber parts with specific performance requirements, and even aerospace applications:

1. Poly(cyclopentene) (poly(CP)) – a homopolymer

• Made entirely from cyclopentene
• Has consistent properties, like flexibility, durability, and cold resistance.

2. Poly(norbornene-ran-cyclopentene) (poly(NB-ran-CP)) – a copolymer

• A blend of norbornene and cyclopentene.
• Norbornene adds toughness, while cyclopentene provides flexibility.

3. Poly(dicyclopentadiene-ran-cyclopentene) (poly(DCP-ran-CP)) – another copolymer

• A combination of dicyclopentadiene and cyclopentene.
• Dicyclopentadiene increases strength and heat resistance, while cyclopentene enhances flexibility.

They first synthesised these materials and vulcanised them at 160°C, creating rubber sheets identical to those used in real-world products. Then came the big test. The researchers used a ruthenium-based catalyst, which gently breaks the vulcanised rubber without damage. Instead of harsh heat or chemicals, it triggers a reaction that restores the rubber’s original building blocks and leaves the sulphur moiety.

For the non-crosslinked poly(CP), the reversal was almost effortless: one hour at room temperature was enough to convert the rubber back into cyclopentene monomer. Crosslinked rubber took a little more effort (60°C and 24 hours), but it still worked. And the results were stunning: around 90% of the original cyclopentene monomer was recovered, along with leftover fillers like carbon black, which could also be reused. This isn’t just another recycling method, it’s true chemical recycling.

Why This Breakthrough Matters

Imagine a future where old tires, industrial rubber, and discarded materials don’t go to waste. Instead, their building blocks are reused over and over again to make new, high-quality products. This closed loop system has been dreamed of for decades.

Now, for the first time, scientists have found a way to fully break down vulcanised rubber, recovering its original monomers without extreme conditions or harmful processes. Instead of burning rubber waste or dumping it into landfills, manufacturers could turn it back into usable materials, dramatically reducing pollution and carbon emissions.

To conclude – A Greener Future for Rubber

There’s still work to be done before this method can be used on a commercial scale. Researchers are now focusing on reducing catalyst usage to make the process more cost effective, improving energy efficiency for large scale applications, and developing strategies to recycle fillers, solvents, and catalysts for an even greener process. They are also exploring potential uses for leftover copolymers, which could have their own unique applications. Most importantly, scientists are figuring out how to scale up this process for industrial use. If this technique can be applied in large scale recycling plants, it could completely transform how the world handles rubber waste.

This discovery proves something astonishing: the chemical bonds in vulcanised rubber aren’t as permanent as we once thought. With the right approach, we can break them and build them back up again. It’s a glimpse into a more sustainable future, one where materials long thought to be beyond recycling can be reborn, not as mere remnants or downgraded fillers, but as the very substances from which they were originally made.

By challenging conventional limits, Dr Hayano and his team from the Zeon Corporation have pave the way for a circular economy in rubber manufacturing, offering industries a chance to move beyond temporary fixes and embrace a fully regenerative system. If this technology can be scaled up and industries adopt its principles, then discarded tires, industrial rubber, and thousands of other products won’t have to meet an end in landfills or incinerators. Instead, they can be repurposed again and again, drastically cutting waste and making rubber production more environmentally responsible.

A future without rubber waste is no longer an abstract dream — it’s a real possibility. And this discovery may well be the first step in bringing that future to life.