Irish start-up advances oxidative devulc process for full tire recycling

Prague – An Irish materials technology start-up has presented a chemical recycling process that it says can recover up to 98% of the materials in end-of-life tires, including rubber, carbon black, steel and textiles.

The company, founded in Ireland in 2020, is building an intellectual property portfolio focused on tackling major global challenges, including rubber recycling, explained Dr Fergal Byrne, chief technology officer at Addible.

Addible's OxyCycle rubber recycling technology involves a chemical oxidative devulcanisation process based on TMO2, a “mild, bio-based oxidant,” and a solvent, he said during the Future Tire Conference 2025, held in Prague in November last year.

The process, according to Byrne, is carried out in four main steps.

In the first stage, shredded or whole tires are placed in the TMO2 solvent. Because vulcanised rubber is cross-linked by sulphur, it does not dissolve, but it swells.

This causes processing oils, plasticisers and waxes to be extracted into the solvent, explained Byrne, noting that around 10–15% of the tire mass is removed at this stage.

Furthermore, the tire structure begins to delaminate, with layers separating around the textile reinforcement.

In the second stage, TMO2 is added, which “selectively attacks” sulphur bridges in vulcanised rubber.

Once those sulphur crosslinks are broken, the rubber polymers are free to dissolve into the solvent.

The tire therefore disintegrates into a liquid rubber solution, while carbon black, steel and textiles remain as solid particles suspended in the liquid.

The mixture is then filtered to produce a “clear to pale yellow” solution of dissolved polymer.

Carbon black, meanwhile, is recovered as a fine powder, steel is removed magnetically and textile reinforcements are recovered intact and clean, retaining their original colour and structure.

In the final step, the system is washed to remove residual oxidant, using hydrogen peroxide as the oxidising agent.

At this stage, Byrne explained, sulphur removed from the rubber is converted into a weak sulphuric acid solution.

The solvent (TMO) is then recovered and recharged with hydrogen peroxide to regenerate TMO2, allowing it to be reused in “a closed loop.”

According to Addible, the process achieves about 98% material recovery, with only around 1% lost, mainly as oxidised sulphur.

Processing oils are also recovered and can be separated by distillation.

The carbon black obtained through the process is produced without the formation of char, unlike pyrolysis, and was described as “extremely fine and undamaged.”

NMR and infrared analysis presented at the conference showed that the carbon–carbon double bonds in the rubber backbone remain intact, confirming that only sulphur crosslinks are broken during the process.

Addressing questions from the audience, Byrne said the process can handle the multiple rubber types found in tires, such as natural rubber, butadiene rubber and butyl rubber in inner liners.

These, he said, can be separated in two ways: mechanically, because tire layers delaminate early in the process, allowing inner liners to be removed before dissolution.

A chemical process can also help separate the rubbers, as different rubbers devulcanise at different rates. By controlling reaction time and conditions, individual rubber types can be selectively dissolved and recovered.

Furthermore, the severity of the process can be tuned to leave more or less sulphur on the polymer chains, depending on what downstream users require.

In terms of development status and partnerships, the technology has been validated at TRL 3 (technology readiness level) on a kilogramme scale in the company’s laboratory.

It recently won a prize from Repak, Ireland’s recycling body, and is now seeking to scale up to TRL 4 and 5, which validate the technology in a lab environment and in an “industrially relevant environment”, respectively.

Byrne concluded by saying that Addible is actively looking for industry partners, particularly tire manufacturers, to test the recovered rubber and carbon black and to help define product specifications.

The goal, he noted, is full circularity, with recovered materials going back into new tires.