Recycled Rubber, Rice Husks and Plastic Bottles: Sustainable Materials in Tyre Production
Car tyres are round, black and made of rubber.
Image supplied by Continental Tyre South Africa
Look closer, however, and you’ll see that the design of tyres and the interaction of the various materials that go into making them are extremely complex. But for some time now, the material experts and tyre engineers at Continental have been bringing about a silent revolution. By 2050 at the latest, all tyres are to be made of sustainable materials. There is still a long way to go until then. But step by step, it is already becoming apparent which raw materials will find their way into tyre construction in the future. These include waste products from agriculture – such as the ash from rice husks – rubber from dandelions, recycled rubber or PET bottles.
Claus Petschick, Head of Sustainability at Continental Tires, is clear about Continental’s mission, saying,
“Continental is on the road toward becoming the most progressive manufacturer in the tyre industry in terms of sustainability. We aim to use 100 percent sustainable materials in our tyre products by 2050 at the latest.”
He adds,
“Our innovative power enables us to break new and even more sustainable ground. This encompasses everything from the origin and sourcing of our materials through to the reuse and recycling of our tyres.”
Already today, around 15 to 20 percent renewable or recycled materials are used in a standard passenger car tyre from Continental. To further increase the proportion of sustainable materials and conserve valuable resources, Continental continuously analyses and reviews all raw materials used in tyre production.
Perfect material matching for maximum safety
Depending on the application, season and environment, tyres have to fulfil specific requirements. This can be seen in, for example, the tread design. But in other areas – the composition of the rubber compound, for example – these changes are not so readily visible. Passenger car tyres from Continental consist of as many as a hundred different raw materials.
Their precise composition has a major impact on the tyres and their handling characteristics. The ability to deploy the various materials with their unique properties and interdependencies in specific ways is a complex balancing act for Continental’s engineers and material experts. Only when all the materials are ideally matched to each other can safe, energy-efficient and durable high-performance tyres be created.
Natural rubber still essential thanks to its exceptional properties
Natural rubber is essential for ensuring outstanding tyre performance. This natural product accounts for between 10 and 40 percent of the entire weight of modern high-performance tyres. Its special properties include the high level of strength and durability, which are caused by the strain-induced crystallization of the rubber.
The tyre industry is the biggest consumer of global rubber production, accounting for more than 70 percent. However, Continental considers natural rubber a sustainable material only if it is sourced responsibly. Therefore, the company employs an integrated approach aimed at making the complex and fragmented supply chains for natural rubber more sustainable, including using cutting-edge digital technology, local involvement and close collaboration with capable partners with the goal of improving transparency and traceability along the entire value chain.
Meanwhile, with its Taraxagum project, Continental is pursuing an innovative approach to ensure that it can become less dependent on natural rubber grown primarily in southeast Asia. The tyre manufacturer is working alongside partners on industrializing the extraction of natural rubber from specially cultivated dandelion plants.
Sustainable plant-based fillers
In addition to rubber, fillers such as silica are essential to tyre assembly. Silica, for example, helps to optimize characteristics such as grip, rolling resistance and tyre life. In the future, rice husks will be used as the source material for sustainably produced silica. Rice husks are a waste product of rice production and cannot be used as food or animal feed. Silica derived from the ash of rice husks is more energy-efficient when used in manufacturing than that obtained from conventional materials such as quartz sand.
Plant-based oils – such as rapeseed oil and resins based on residual materials from the paper and wood industries – already offer an alternative to crude oil-based fillers in Continental's tyres. Only oils that meet technical quality standards and are not suitable for consumption are used. Oils and resins allow for flexibility in terms of tyre compounds, and so improve the material’s grip.
Expanding the circular economy
Continental is aiming for fully circular operations in its tyre production by 2050 at the latest. In addition to the use of renewable materials, the company is working systematically on using recycled raw materials in tyre production. This is intended to ensure that carbon black – another crucial filler in rubber compounds – can be obtained on a large scale in the future. Continental recently signed a development agreement with Pyrum Innovations with a view to further optimizing the recycling of materials from old tyres.
To do this, Pyrum breaks the old tyres down into their constituent parts in an industrial furnace using a special pyrolysis process. In this way, valuable raw materials contained in end-of-life tyres can be extracted and recycled. Both companies are working towards obtaining high-quality raw materials from the pyrolysis oil obtained for Continental's tyre production in the medium term, in addition to the direct use of high-quality carbon black. In the long term, the premium tyre manufacturer and Pyrum are aiming to establish a closed-loop circular economy concept for the recycling of old tyres.
Recycled rubber from end-of-life tyres
In addition to pyrolysis, Continental is also making use of mechanical processing of end-of-life tyres. Rubber, steel and textile cord in particular are separated, in a highly sophisticated process, from one another. The rubber is then prepared for re-use as part of new rubber compounds.
Continental has a long history of working consistently to introduce end-of-life tyres into the circular economy to conserve resources and the environment. A material known as “Conti-Reclaim” has been obtained as part of the truck tyre retreading process at the company’s plant in Stöcken in Hanover since 2013. It has been used in tyre production at Continental for years. To expand the range of applications for the recycled rubber and optimize the properties for the various fields of application, Continental uses not only “Conti-Reclaim” but also recycled rubber from other suppliers.
Recycled plastic bottles in tyre casing
“Recycled raw materials are going to play a big role in making tyres more sustainable. We use recycled materials whenever possible. Comparable quality and material properties to conventional raw materials are crucial for us,”
says Petschick.
For example, Continental is working with partners to obtain high-quality polyester yarn for its tyres from recycled PET bottles. PET bottles often end up in incinerators or landfills otherwise. With its ContiRe.Tex technology, the tyre manufacturer has developed a more energy-efficient and eco-friendly alternative that allows it to reuse between nine and fifteen plastic bottles for each tyre, depending on the tyre size. The recycled PET has already replaced conventional polyester in the structures of some tyre casings. The PET bottles used are sourced exclusively from regions where there is no closed recycling loop.
Systematically moving toward greater sustainability
Continental is working tirelessly to advance innovative technologies and sustainable products and services throughout its entire value chain, from sourcing sustainable materials to recycling end-of-life tyres. The company is aiming to achieve 100 percent carbon neutrality by 2050 at the latest.
