Tyres: A fresh look at recovery solutions for old tyres

April 3, 2019

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Tyres that have seen better days may be imputed as pollution contributors; however, new developments are changing this notion about end of life tyres (ELTs), says Angelica Buan in this report.

Worn-out tyres spell danger for millions of commuters and motorists who are at risk of road accidents. The World Health Organisation (WHO) estimates that nearly 1.4 million people figure in road traffic crash related fatalities each year.

Vehicles with worn-out tyres are thrice as likely to end up in a crash, according to US’s National Highway Traffic Safety Administration (NHTSA).

On a macro scale, worn out tyres not only pose traffic hazard, with a study revealing that worn out tyres also contribute to air pollution.

A recent Tire Industry Project (TIP) study has investigated the potential contribution of tyre and road wear particles (TRWPs), being non exhaust sources, as well as vehicle exhaust to airborne particular matter (PM or smaller than 2.5 micrometres in diameter) in several major urban centres. Based on the study, which covers analysis of urban roadside air samples from London, Tokyo and Los Angeles, tyre wear comprises a small percentage of total PM2.5 in ambient air.

Every time tyres are used on the road, TRWPs are produced by the friction between tyres and the road surface. TRWP are a mixture of tyre tread material and elements from the road surface. These tiny particles are readily inhaled, and thus have impact to human health.

According to the study: “Samples indicated that TRWP concentrations in the PM2.5 fraction were low, representing an average contribution to total PM2.5 of less than 0.3%. However, the study found significant differences in TRWP contribution to PM2.5 between the three cities, and no significant correlation between TRWP in PM2.5 and traffic count”.

For now, the findings are not conclusive. The authors emphasised that further research is needed, starting with additional sampling for TRWP in ambient air that would help establish the extent of how tyre wear contribute to non-exhaust PM emissions to ambient air.

As the study indicates that properly checked and inflated tyres not only prevent road mishaps but also air pollution.

Waste tyres as source of microplastic pollution

In yet another study, car tyres were assessed to contribute to the microplastic onslaught in the UK waterways and soils.

The UK study, Reducing Household Contributions to Marine Plastic Pollution, carried out by Eunomia Research & Consulting and Friends of the Earth (FOE) was published in November last year. It estimates that of the four major sources of microplastics, including plastic pellets, paint, and clothing, vehicle tyres release up to 68,000 tonnes/year of microfibres produced from tyre tread abrasion into the environment. Of this volume, between 7,000 and 19,000 tonnes enters surface waters.

The Netherlands-headquartered environmental organisation FOE indicated that vehicle tyres shed plastic particles that are a mixture of natural and synthetic rubber, and well as various additives, during driving; and are believed to be responsible for the greatest proportion of microplastic pollution entering Europe’s waters. Up to 10% of tyre wear is generated as airborne particles, which can also settle in the surrounding areas where their impact is not known. Since the particles vary in size and composition, identifying and tracking exactly where they go can be difficult as they can be widely dispersed around roads and washed away during rain, the study proponents said.

Additionally, their buoyancy in water varies and much of the particles would likely settle into river and estuary sediments where they may still interact with river wildlife.

To remedy this, FOE suggests a number of measures to tackle tyre car pollution, including car tyre levy, a standardised test to measure tyre tread abrasion rate, and integration into the current tyre labelling scheme. Moreover, the group seeks for an action plan that targets near zero plastic pollution by 2024.

Recovering the value of waste rubber with technology

At some point, worn out tyres will have to be done away with. Unfortunately, a significant bulk of end of life tyres (ELTs) is either landfilled or incinerated. Furthermore, run of the mill recycling facilities are not accepting tyres because they are not considered household wastes, not to mention their lack of applicable technologies to process them.

Globally, an estimated 1 billion/year waste tyres are generated, but only 10% or 100 million are recycled. Because the tyre’s design is made complex by the various materials that go into manufacturing it, it makes it difficult to recycle.

Nevertheless, new technologies for tyre recycling are being developed to serve the growing recycling market, poised to cross US$9.5 billion by 2022, according to a forecast by BCC Research.

One such new innovation is offered by Danish company, Eldan Recycling. The Twin Shaft Clean-Cut Shredder (TSCC) is developed for the production of clean-cut tyre chips from car or truck tyres.

It features two frequency converters to ensure a very flexible operation; and promises up to 50% power saving. The TSCC can produce clean-cut 50 mm chips from car or truck tyres at up to 6,000 kg/hour, or clean-cut 100 mm chips at up to 9,000 kg/hour.

China advances into green recycling

China is one of the world’s major producer of rubber products, tyres being the largest product segment due to its rapid motor vehicle production. The growing consumption also translates to increasing wastes.

Since China generates approximately 100 million pieces/year of waste tyres, the country takes recycling seriously. Apart from its adoption of internet-based or “smart” recycling hubs, it also has built the 7.5 million sq ft-Central China Rubber Resources Recycling Industrial Park located in Xiangyang, Hubei Province, which can process 400,000 tonnes of ELTs and converts rubber scraps for a variety of applications.

A more recent development in China’s recycling innovation is a smart industry 4.0 factory. It has been built by Chinese tyre manufacturer Doublestar in Runan, in the Henan Province.

Utilising a green pyrolysis and carbon black regeneration technologies, the facility is claimed to have the capability to recycle waste tyres without causing pollution. It will have a capacity of 200,000 tonnes/year of scrap rubber; and can process 100,000 tonnes of waste tyres, and produce 45,000 tonnes of pyrolysis oil and 35,000 tonnes of carbon black.

New use for old tyres in the construction sector

Old tyres and rubber scraps also find suitable applications in major industries. For example, fibres from old tyres can reinforce fire resistance of concrete, according to a study from University of Sheffield in the UK.

Using fibres extracted from the tyre’s textile reinforcement, the team added these fibres to the concrete mix to reduce the concrete’s proneness to fire spalling. The fibres, under the intense heat of a fire, would melt, while at the same time help reduce the pressure within the concrete to prevent it from breaking out explosively. Moreover, the fibres protect the steel reinforcements running through the concrete during a fire.

The Sheffield study showed that the fibres reclaimed from used tyres could perform as well as the raw materials like virgin polypropylene (PP) fibres, but with less energy than when producing the latter. The results are published in the journal Fire Technology.

Working with Twincon, a Sheffield-based company that develops solutions for the construction industry, the researchers also developed technologies that turn the tyre polymer fibres from waste to usable construction materials, and to ensure that they are dispersed uniformly in concrete.

Reportedly, the testing of the material on different ratios and with different types of concrete; as well as on the behaviour of the fibres to heat at the microstructure level, has been successful.

In a similar undertaking, German speciality chemicals group Evonik has also developed a new material called Vestenamer, a process additive for the rubber and construction sectors. With Vestenamer, rubber powder can be processed from scrap tyres to generate asphalt with rubber content. The recycled material is mixed into road construction bitumen or asphalt to improve the quality of the mixtures and to extend the service life of road surfaces.

Vestenamer not only enables extended road service life, but likewise helps to curb traffic noise by using the powder in porous low-noise asphalt. More significantly, according to Evonik, is Vestenamer’s capability to reduce the migration of organic compounds like hyrdocarbons and sulphur that are washed out by rain and reach the groundwater; and thus its use reduces the overall groundwater burden.

Elsewhere, old tyres are the main ingredient in this seismic innovation by a research team from New Zealand’s University of Canterbury. Led by Gabriele Chiaro, a UC senior engineer lecturer, the team worked on a project dubbed the “eco-rubber seismic-isolation foundation systems” that will improve the seismic resilience of low-rise buildings across New Zealand. It has been approved for funding of US$1 million by the Ministry of Business Innovation and Employment.

The seismic rubber system can be achieved by combining two critical elements, namely, a seismic-dissipative filter made of rubber-gravel mixtures placed underneath the foundation structure; and a flexible raft foundation made of steel fibrereinforced rubberised concrete.

These new advancements indicate that while waste tyres are increasing, this should not be inimical to the environment, if recycling and recovery solutions are in place to harness the value of old tyres, which is a cheap resource.

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