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The tire-to-tire model revealed

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The tire manufacturing industry is transitioning to a circular economy by adopting a cradle-to-cradle approach.

The drive towards sustainable production comes from EU regulations, increasing shareholder pressure, and consumer demand for clean, green products. Hence, the industry is setting ambitious targets to close the material loop with a tire-to-tire model. Keep reading to learn about the methods the tire industry is using to reach its targets.

What is the tire-to-tire model?

The tire-to-tire model closes the material loop in tire production. End-of-life tires (ELTs), dumped into landfills or incinerated for energy, are now being recycled using various techniques to recover materials. These secondary materials from tire recycling are then used to make new tires.

Material recovery from ELTs happens through mechanical recycling, and most products can also find applications outside the tire industry.

The tire-to-tire model reuses old tire materials to make new tires. ELTs are a valuable resource, and several technologies can be used to recover the materials as alternatives to standard virgin fossil fuels-based raw materials.

Table 1: Components of tires.

(Credits: Study on End-of-Life Tires (ELTs) Recycling, Strategy, and Application)

As shown in Table 1, though composition varies across countries, natural rubber constitutes less than 30 per cent of the materials used to make tires. The remaining 60 per cent comprises petroleum-based synthetic rubber, virgin Carbon Black (vCB), and textiles and steel that are easy to recycle.

Careful research, planning, and management are required to recover these material components from ELTs and ensure they reach an appropriate end-use. In addition, policy support and awareness will also be necessary for all stakeholders, including the public, which are one of the primary consumers of tires.

A shift to a circular tire-to-tire manufacturing model will require collaborations upstream and downstream between manufacturers, retailers, consumers, and tire recyclers to ensure efficient material supply management.

Though material recovery has improved globally in the last two decades and is up to 94 and 95 per cent in the USA and EU, respectively, recycling has not kept pace with the number of discarded ELTs. Therefore, there is room for disruptors in the tire recycling sector.

Tire-to-tire developments: targets for circularity

Some of the tire-to-tire approaches and targets of various manufacturers are discussed below.

  1. Pirelli aims to manufacture select tires using at least 40 per cent renewable materials, three per cent recycled materials, and less than 40 per cent raw materials from fossil fuels by 2025. Its tires currently contain less than 20 per cent recycled and renewable components. Pirelli uses the recycled product recovered Carbon Black (rCB) and regenerates it from unvulcanised rubber. The company hopes to use more of these materials as the mechanical properties of recycled materials improve to match its manufacturing needs.
  2. The Michelin Group’s 2050 target is to produce tires entirely from recycled, biological, or renewable sources. Currently, 30 per cent of the materials used in Michelin’s tires fit into these categories. Michelin Group partners with innovative startups, companies, governments, and public entities to promote the tire-to-tire manufacturing model. The company has also started its recycling plant with a partner to recycle ELTs. The Michelin group is also radically rethinking tire design through R&D efforts by making 3D-printed airless tires that will completely change the look, manufacturing, and disposal flow of tires.
  3. Rubber crumb of 0.1 to 0.45 mm, produced from mechanical recycling, is used in rubber mixtures to make new passenger and massive tires. Reclaimed rubber can be up to four times cheaper than new rubber, and its use in tire-to-tire models is widespread across the globe. However, only 5-20 per cent of existing rubber crumb is used as an additive for manufacturing new tires. At these proportions, the curing properties of fresh rubber and crumb mixture change only moderately. Also, not all rubber crumb is useful for tire manufacture: smaller particles produce better mechanical properties than larger ones.
  4. Devulcanisation attempts have been successful only in the laboratory. The commercialisation of the technology has been historically difficult to achieve so far. Tyromer, a Canadian firm, is setting up a new pilot plant in Arnhem, Netherlands, which can devulcanise natural and synthetic rubber from car tires, and industrial rubber to new rubber. Devulcanisation breaks down the sulphur bonds that make rubber stiff and prevent it from melting. Consequently, devulcanised rubber has a flow and malleability that matches virgin rubber.

The role of recovered Carbon Black in the tire-to-tire model

Another recycled product that shows great promise for use in tire-to-tire models is rCB.

Carbon Black (CB) is the second major tire component (see Table 1). It’s used as a filler in natural and synthetic rubber mixtures, along with additives and chemicals. CB’s mechanical properties are crucial in making tires strong and durable.

Most CB in tires is vCB made from fossil fuel products. However, to make tire manufacturing circular, prominent tire brands are replacing some of the vCB with rCB. This move has become possible due to the development of modern tire pyrolysis technology.

Tire pyrolysis decomposes ELT rubber crumb by applying high temperatures in oxygen-free atmospheres to yield the component raw materials like rCB, steel, pyrolytic oil, and pyrolytic gas. Each of the pyrolytic products has a use in the tire-to-tire model.

rCB can replace 20 per cent of medium-grade vCB without affecting tire properties. The direct use of rCB in tire-to-tire manufacturing makes it a huge win. Moreover, since CB makes up around 22 per cent of a tire, replacing 20 per cent of fossil fuel-based vCB with rCB has positive environmental benefits.

The pyrolytic oil produced during the tire pyrolysis process can be used to make a large to medium-grade vCB, ensuring that even more components of tires are circular and sustainable. The steel can also be reused to make new tire rims and wires. Tire pyrolysis processes can recycle 85 per cent of an ELT’s components into materials and the rest into gas. This gas can serve as a renewable fuel for the pyrolysis plant.

Contec’s role in the tire-to-tire model

There are not many tire pyrolysis plants in Europe. One of these is operated by Contec, which developed its own protected pyrolysis process. Contec is actively involved in the tire industry to push it toward circularity. For example, Contec supports the RCB Rubber initiative by tire manufacturers, which aims to incorporate rCB in their tire-to-tire model. We also actively maintain regional collaborations with tire industry stakeholders to recycle ELTs and make circular products. Get in touch to learn more about our sustainable solutions.

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