The production of safer, more durable, and more efficient tyres has come far since the first tyre.
One area now receiving more attention is recycled materials in tyre manufacturing. With concerns over environmental impact and sustainability, the tyre industry is looking for ways to reduce its carbon footprint and minimise waste. Using recycled materials in tyre production is one way of achieving these goals.
The most used material in tyre production is natural rubber sourced from the rubber tree sap and synthetic rubber made from petroleum. In addition to these materials, tyres contain other components such as steel, nylon, and carbon black. These latter elements improve performance and durability.
Recycling is an effective way to reduce waste and the use of raw materials. The most used recycled material in tyre production is crumb rubber. Crumb rubber, alternatively known as ground rubber, is made by grinding up used tyres into small pieces.
However, some companies are taking this even further, and for some time, 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% sustainable materials in our tyre products by 2050.
Already, around 15% to 20% renewable or recycled materials are used in a standard passenger car tyre from Continental. To increase sustainable materials proportions and conserve valuable resources, Continental continuously analyses and reviews all raw materials used in tyre production.
Considering the application, season and environment, tyres must fulfil requirements. For example, the tread design meets these requirements. 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 impacts the handling characteristics of tyres. The ability to deploy the various materials with their unique properties and interdependencies in specific ways is a complex balancing act for engineers and material experts. Only when all the materials combine can safe, resistant optimum tyres are created.
Natural rubber is essential for ensuring outstanding tyre performance. This natural product accounts for between 10% and 40% of the entire weight of modern high-performance tyres. Its unique properties include a high level of strength and durability, which emanate from the strain-induced crystallisation of the rubber.
Crumb rubber is a multipurpose, versatile material. Apart from tyre manufacturing, it is suitable for asphalt and other construction materials, as well as for playground surfaces and other applications.
One advantage of crumb rubber is that it reduces carbon footprint and waste. Used tyres are a significant source of waste and recycling them reduces the amount of waste in landfills.
Another advantage of using recycled materials in tyre production is that it can make the tyres more durable. Crumb rubber is a strong and resilient material that can withstand heavy use and extreme conditions.
In addition to rubber, fillers such as silica are essential to tyre assembly. Silica, for example, helps to optimise characteristics such as grip, rolling resistance and tyre life. The future will see rice husks as the new source of material for sustainably produced silica.
Rice husks are an unwholesome waste product of rice production. Silica derived from its ash is more energy-efficient 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 tyres. Manufacturers only use oils that meet technical quality standards and are unsuitable for consumption. Oils and resins allow for flexibility in tyre compounds and improve grip.
Carbon black, another crucial filler in rubber compounds, is also under the spotlight. Continental recently signed a development agreement with Pyrum Innovations to optimise recycling materials from old tyres.
To do this, Pyrum breaks the old tyres into their constituent parts in an industrial furnace using a pyrolysis process. 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 tyre production in the medium term, in addition to the direct use of high-quality carbon black. With the future in mind, Continental and Pyrum plan to establish a closed-loop circular economy concept for recycling old tyres.
“Recycled raw materials will 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.
Recycled PET has already replaced conventional polyester in the structures of some tyre casings. The PET bottles are sourced exclusively from regions with no closed recycling loop.
