Groups unite at crunch time for tire recycling

Based on article published in the November/December issue of European Rubber Journal magazine.

What to do with the almost 1 billion tires produced in the world each year – equivalent of 13.5 million tonnes of raw materials – at the end-of-life stage remains a vexing question right across the industry supply chain.

The issue brought leaders of the main industry associations representing tire recyclers and tire manufacturers in Europe together for the first time in years, during the Bureau of International Recycling (BIR) World Recycling Convention, 26-27 Oct in Prague.

The forum was the BIR tyres & rubber committee meeting, where Fazilet Cinaralp of the European Tyre and Rubber Manufacturers’ Association (ETRMA) and Dr Valerie Shulman of the European Tyre Recycling Association (ETRA) shared a platform along with Dr Wilma Dierkes of the University of Twente.

Welcoming what he described as an “historic meeting of people who have not been meeting each other for years,” BIR tyre committee chairman Ruud Burlet emphasised the need for manufacturers and recyclers to unite to address common issues.

“The only way we can counter the threats and make use of the opportunities is if we cooperate, join forces and stand as one,” said Burlet, who is also managing director of recycling company Rubber Resources BV, based in Maastricht, The Netherlands.

Endorsing the call for unity, ETRMA secretary general Cinaralp listed shared challenges as including: producer responsibility; standardisation; and balancing the requirements of the EU’s circular economy agenda with the objectives of the REACH chemicals safety regulations.

“We are really entering a new era, where we have to organise ourselves to ensure this raw material [from end of life tires (ELTs)] is used in the best possible ways,” she said. “We need to find a way of truly working together and having a constructive dialogue.”

For the recyclers, ETRA secretary general Schulman emphasised the need for recyclers to have good quality market information, particularly on scrap tire arisings, and for clearer legislation.

“A lot of tire-related legislation appears to be somewhat outdated,” she said. “We have to look at [how that works] for recycling of tires and other products.”

Shulman went on to highlight the progress of the ETRA in helping to further develop applications of scrap rubber, for example in road-building and construction materials.

“We are not just doing the preliminary research,” she said. “We are following up with marketing and development. That is where we at ETRA feel we have to take the lead and move ahead with all of you.”

Level playing field?

The importance of unity among all sections of the industry is underscored by the European Commission’s soon-to-launch Circular Economy Package – a broad sustainability initiative to eliminate waste and return materials from end-of life products back to the manufacturing chain.

These worthy goals, however, raise some serious potential problems for industry, not least because they conflict with ongoing EU moves to tighten restrictions on chemicals under the REACH regulations.

A clear example here is EC-PAH Restriction on Consumer Products Regulation 1272/2013, which will ban the sale of articles containing 1mg/kg of listed PAHs from “skin contact” applications, from the end of 2015.

The EC’s list of articles covered by the regulation includes, among other products, sports equipment, household utensils, DIY tools, clothing, footwear and other products designed to be worn.

According to Burlet, there is particular concern that the banned products will include sports fields and other playing surface applications, which use large quantities of tire rubber.

“If that comes down, it will really be very difficult to use recycled tires in these applications. This is already on the verge of happening, so you really have to counteract this,” he told the BIR committee meeting in Prague.

There are still question marks over whether the regulation applies to synthetic turf and shock absorbing surfaces, which together make up over 54 percent of the market for recycled rubber granulate.

Sports fields are the biggest market for recycled rubber, with 1,300 fields installed annually and 1.1 million tonnes for ELTs processed for this application in Europe alone, noted Cinaralp.

“We cannot find any scientific evidence of concern, not in Europe, not in the US,” said the ETRMA leader. “Some studies have been carried out, showing that there are no significant health effect from playing on these surfaces.”

Media scare stories in the US, meanwhile, have prompted authorities there to initiate studies into potential health risks from playing on synthetic turf.

Whether or not these applications are included in the scope of new regulations – a decision in the EU was pending as ERJ went to press – there remains a wider concern about the decline in added-value applications for ELT rubber.

Use in synthetic turf itself, for example, has fallen from 43 percent in 2011 to 30 percent last year, while asphalt rubber fell from 4 percent to 1 percent – partly due to reductions in public spending by local authorities.

Another negative trend in the scrap tire market is a shift to burning tires for energy recovery at the expense of recycling. This, said Cinaralp, “indicates that we are reaching challenges in some important applications.

Similarly, Shulman voiced concerns about retreading rates, which she reported have fallen in the EU from 12 percent to 6.5 percent over recent years.

Recyclers, meanwhile, “are really disappointed by lack of government support for their own so-called green economy,” said the ETRA chief – pointing in particular to public procurement policies in EU member states.

“Perhaps if we work together to stimulate government to begin to look at these products as valuable results of the recycling society and material available for them to use, we might make some additional progress,” she commented.

Back to the routes

Burning tires for energy is at the lowest level of recycling, agreed Dierkes of the elastomer technology and engineering department at the University of Twente in The Netherlands.

The ultimate goal, she said, should be converting “tires back into tires” as this is the only way to considerably broaden the market for recycled rubber.

In the EU alone, around 2.4 million tonnes of rubber; 1.2 million tonnes of filler (carbon black and silica): and 681,820 tonne of steel and wire are used each year in tire production.

Reviewing current options for converting ELT waste streams back into valuable raw materials, Dierkes noted that tires can be ground down back into granulate of varying degrees of fineness.

However, she said, the quality can be low with the possibility of contamination, for example from tire cord, a common problem. Lower-cost, coarse rubber granulate is typically used in road construction, as well as floorings, artificial turf and lower quality rubber products.

Costs, however, increase exponentially with fineness and it can be a challenge to produce clean and consistent products, especially using materials from different parts of the tire, said Dierkes.

Many of these inherent problems can be overcome by devulcanising the rubber back to the starting polymer molecules. However, the heat and pressures involved often mean the end material is below the quality required for large-scale commercial use.

Researchers at the University of Twente have, therefore, been developing devulcanisation technologies for both natural and synthetic tire rubber, using lower temperatures and shearing forces to minimise polymer breakdown.

In tests, optimised compounds containing the recycled SBR – the most difficult rubber to devulcanise – at levels of 25-40 percent, more or less matched the tensile strength, modulus and hardness of virgin SBR compound.

Further improvement has been achieved using continuous devulcanisation of SBR in an extruder under a protective atmosphere and with intensive cooling of the devulcanisate – within a project called RecyBEM (see table left).

“This is quite promising and we are still working on this process,” said Dierkes, adding that R&D is now on-going to upscale the technology to a continuous extrusion process and address issues around the quality of feedstock needed.

Pyrolysis

Another approach is back-to-feedstock pyrolysis, which typically features large-scale batch facility that require high investment costs. It can also be difficult to control temperatures and other parameters during the process.

Pyrolysis char is often contaminated with silica, zinc oxide and burnt polymer and the structure and surface differs from virgin carbon black. There are also risks of contamination by aromatics and sulphur compounds.

“We need a quantum leap in the quality of the char to be able to have wider applications in tires,” Dierkes commented.

A promising development in the field of pyrolysis is flash liquefaction – a continuous, extremely fast conversion process, which requires relatively low process temperatures resulting in high-quality products. The process uses a catalyst swollen into the rubber by an oil that also accelerates heat transfer within the material.

Overall, though, Dierkes said that applications for grinding and pyrolysis were likely to remain limited and that the industry should concentrate more on devulcanisation “because then you can get the material back to the tire.”

The goal of reusing scrap rubber in tires is “a reality to come because we don’t have a choice in terms of resources, requirements from society and environmental policies,” concluded Dierkes. “This will become an obligation for rubber manufacturers.”