How tyres are turning green

Tyres hide a feat of engineering beneath their nondescript black outer layer. Around 200 different raw materials come together to ensure car tyre performance, durability and safety. During recent years, the tyre industry has steered significant research and development efforts towards increasing the sustainability of these materials. Currently around 20% of materials in a typical car tyre are renewable or recycled with many of the rest derived from petroleum. Many manufacturers have pledged that their car tyres will contain 100% renewable or recycled materials by 2050.

One of the reasons for the slow paced transition is the complexity of tyre design. Each material in a tyre has a specific job within the broader matrix, explains Adam McCarthy, secretary general of the European Tyre and Rubber Manufacturers’ Association (ETRMA) in Brussels, Belgium. ‘It takes time to identify potential substitutes,’ he says, adding that the strong focus on safety also tends to put the brakes on progress. ‘The first and the last priority is always going to be safety.’

Compositions vary between manufacturers, tyre types, and price points, but most tyres share the same layered construction. There is the predominantly-rubber tread – the outer edge that makes contact with the road – and outer side wall. Beneath the tread is a supporting belt, often made up of steel cords. A skeleton layer, comprised of textile fibres, sits under the belt and the side walls. Then, there is a steel loop around the inner lip of the tyre where it meets the wheel.

Alternatives to nature

Rubber is the most abundant material in tyres. A car tyre is typically 20–30% natural rubber and a roughly an equivalent amount of synthetic rubber. The primary source of natural rubber is the sap of the rubber tree (Hevea brasiliensis) that grows in tropical regions. Despite being a natural polymer, rubber production has caused considerable environmental damage due to the deforestation of tropical rainforests to meet increased rubber demand.

In 2015, Michelin became the first in the tyre industry to commit to not using rubber from deforested areas. Today, more than 75 tyre and car manufacturers, including Bridgestone and Continental, and other interested stakeholders are working together to reduce the environmental impact of rubber plantations through the Global Platform for Sustainable Natural Rubber. This group educates farmers on more sustainable and higher-yielding production techniques, says Cyrille Roget, Michelin’s scientific and innovations communications director based in Clermont-Ferrand, France. Deforestation-free natural rubber ‘is a renewable material and sustainable’, he explains.

Over the past decade or so, some tyre manufacturers have explored the viability of two alternative natural rubber sources: the guayule shrub (Parthenium argentatum), that stores most its rubber in its bark, and Russian dandelion (Taraxacum kok-saghyz), that stores rubber in its roots. Both plants were researched during world war two, after Japanese forces seized Asian rubber plantations. Once rubber supplies from rubber trees became freely available again, interest in alternative sources of rubber dwindled for nearly 60 years.

A dedicated research center was opened by Bridgestone in the US state of Arizona in 2012 to restart the exploration of guayule’s potential. The aim is to ‘diversify the supply chain to make it more resilient’, explains Bill Niaura, executive director of sustainable innovation and circular economy at Bridgestone Americas, based in Ohio. ‘Hevea is grown in a concentrated part of the world using a single species of plant,’ he says, which puts global rubber supply at risk from disease, climate change and political instability.

Three years after opening the research centre, Bridgestone produced a guayule rubber demonstration tyre. Since 2022, a racing tyre with guayule rubber side walls has been used at IndyCar races. Today, research is ongoing as to how to scale production up. Bridgestone has a demonstration scale biorefinery at the Arizona site that processes guayule grown at on nearby farm. Ongoing research efforts include using genomic tools to grow more rubber in the crop, developing less destructive harvesting methods, and finding commercial uses for resin byproducts from the biorefinery.

Continental was the first to re-evaluate the viability of the Russian dandelion for industrial scale natural rubber production – in 2011. The long-term goal is ‘to grow a certain share of the rubber we consume next to our production facilities’, explains Pete Robb, marketing director at Continental in London, UK. Continental made its first demonstration tyre containing dandelion rubber in 2014 and opened a dedicated dandelion rubber research facility in Anklam, Germany in late 2018. Here, researchers are working on boosting rubber yields using conventional breeding methods and novel field machinery able to harvest dandelion roots without damaging them. ‘The aim is to harvest one metric ton of rubber per hectare of cultivated dandelions, which roughly corresponds to the yield from one hectare of traditional rubber trees,’ Robb says.

Read More: Here