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08/01/2020
Tire recycling still an unsolved issue

Recovering end-of-life tires represents a crucial activity in today’s industrial framework: what can be said about its future, also in the light of significant environmental issues?

Nicodemo Angì

Tires, we all know what they are. However, this familiarity can be quite deceptive: they are in fact sophisticated products, the result of huge investments in research, development and production. Furthermore, this commitment continues even after a tire’s first useful life: recycling/reuse is important in safeguarding the environment and salvaging precious raw materials.

Activities that are now consolidated, but how will they evolve over time? The question is important and the answers, as expected, are rather articulated.

In the USA, for example, forecasts speak of alternative ways of reusing recycled tires compared to what is happening today. According to data from the U.S. Tire manufacturers association (Ustma), the recovery of ELTs is producing good results: in 1991 stocks accounted for more than 1 billion tires but by 2017 these had been reduced to 60 million. At the same time recycling has increased. Although tire-derived fuel still represents the biggest business opportunity, its market share has been eroded by natural gas, cheaper and cleaner.

 

Rubber roads

Industry experts believe that other applications will soon become the norm, such as modified asphalts with rubber powder. And not only that. Some are already using ELTs for soundproofing, in constructing athletic tracks and special floors for animal farms. In Europe, in 2013, ELT recovery had reached 98% compared to 75% recorded in 2004, thus minimising stocks. Data from Etra (European tire recycling association) for 2016, tell us that the EU used 117,000 tonnes of ELTs for civil engineering and other purposes.

 

Innovative applications

The breakdown of the various types of treatments between 1995 and 2014 saw energy recovery fall from 53% to 37%; re-use and retreading of partially worn tires fell from 34% to 27% and recycling went up from 13% to 35%. More recent data, as of October 2018, indicate that 75% of European end-of-life tires are destined as raw material. As the European rubber granules market was quickly saturated a couple of years ago, new applications were needed to develop tire recycling. Among them, Etrma proposes to increase the use of these granules in the production of cement and asphalt, defined as a "very promising market", and athletics tracks. Other areas of interest are soundproofing, vibration damping and reusing recycled rubber in belt plies.

 

Expert’s opinion

We interviewed Giovanni Corbetta, general manager of Ecopneus, familiar with anything that relates to tires given his previous experience at Pirelli. We could not help starting our conversation from the recent decree that regulates the End-of-Life stage of several products which can become "second raw material" rather than waste. First diapers and tampons and now it's the turn of tires: a journey that lasted several years, at the end of which, the Ministry of the Environment, the Ministry of Health, the Higher Institute of Health, Ispra and CNR, all playing a major role, produced a specific regulation on the matter. The bill has also passed the examination of EU bodies and will shortly be published in the Official Journal.

What is now a state law will give new impetus to the use of recycled tires. Just think of granules and rubber powder: their use was previously granted thanks to agreements between a single company and local authorities, which established that these were not waste. Thus these measures had a non-national value.

 

The law that was missing

Geographical limitations have so far proved a real limitation for national bodies, such as Anas, as these could not deal with non-homogeneous local regulations. The Authority that manages the road system has always recognized the technical advantage of using asphalt mixed with rubber powder, however the quagmire of local regulations prevented the widespread use of that specific option. Now, with the new law, Anas will be able to use modified asphalt everywhere, capitalizing on the resistance and noise reduction as intrinsic benefits of this solution. Maintenance costs will drop, acoustic comfort will increase and the community as a whole will benefit.

The Regulations are rather strict, even when compared to other European countries, protecting the environment, and Corbetta hopes this technology will receive the attention it deserves. Its complexity will require some sacrifices, and some will likely try to get around it, that is why careful checks are required.

 

Promising experiments

Giovanni Corbetta described other methods of dealing with ELTs, talking about a process of hot decomposition in the absence of oxygen, called "pyrolysis". This process makes it possible to obtain a combustible gas, a liquid fraction and a solid residue, with the last two still being a problem when it comes to their use. The liquid is a heavy oil suitable for marine engines but hardly suitable for cars also because of its sulphur content, illegal and corrosive. Also its marine use is fast becoming an issue due environmental reasons, while the solid fraction appears to be quite promising, especially as rCB, recovered Carbon Black. The gas is used for heating and the idea, the object of an experiment conducted in Italy, is supplying energy through microwaves: rubber is a good insulator and thus heat spreads slowly, but with this method the material heats up from the inside uniformly, which speeds up the process and makes it more uniform.

 

Future scenario

On the other hand, decomposing tires through the use of a high pressure water jet (600 bar), has proved less promising due to a rapid loss of pressure a few inches from the nozzle. Once the belts are reached the process stops and further problems have been experienced even with very deep treads typical in farming and earthmoving tires. The rubber gets soaked and it is necessary to dry it, slowing down again a process that is currently able to manage only a few tires per hour against the 3/4 tons through a mechanical process.

The process is able to partially de-vulcanize the rubber, which can then be used in making new tires, but fortunately also the ultra-fine powder, from 400 to 75 microns, can be used directly in a new compound. The very small size in fact causes a partial fracture of the sulphur bonds, and this powder, produced for example by Lehigh Technologies, can be added up to about 10% of the total compound.

According to Giovanni Corbetta, in five years even sports facilities will be massively affected by recycled rubber; since these materials are so resistant, the renovation of sports surfaces will be less frequent. The End-of-Waste regulation will also give a significant impetus to the use of recycled rubber in road pavements. Some consider superior durability as a disadvantage for the industry, but there are so many roads that need maintenance that work will still be there for decades. Pyrolysis treatment to recover valuable Carbon Black as well as the use of micro-rubber-powder is expected to soar in the near future. The more applications we can find for used tires, the more profitable the recovery of these materials will be, which may reduce the waste disposal tax. Ecopneus, like other consortia, is non-profit organization, therefore the only goal behind recycling is the benefit this represents for motorists, reducing our dependence on producing countries and help the trade balance.

 

 

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