Intelligent processing solution for complete recycling of end-of-life tires

When recycling end-of-life tires, one last piece had always been missing – the textile fibers. Up until now, they had largely been processed into alternative fuels and combusted. A new process now converts these textile fibers into a novel product that can be used in road construction. And the best part: it makes roads more durable and safer. A win-win situation for recyclers and the environment:

While there are good applications for rubber and metal from end-of-life tires, the textile fibers have been excluded from the tire recycling process up until now. This portion – which accounts for around ten percent of the tire – was mostly processed via thermal recycling as an alternative fuel for the cement industry.

However, for some time now, recycling companies have been facing new challenges, as sectors such as the cement industry are no longer absorbing the full volume of alternative fuels due to the downturn in the construction industry. This then means that recycling companies are left with the textile fibers. At the same time, their approved storage capacity is rapidly dwindling, and the fibers also pose a considerable fire risk.

Unutilized capital is tied up in the textile fibers. Plant engineering specialist Zeppelin Systems has many years’ experience as a solution provider for the rubber and tire industry and has set itself the goal of making tomorrow’s tire production more sustainable today.

The company launched the Zeppelin Sustainable Tire Alliance and acts as its patron. Together with its international partners, the technology alliance pursues the mission of making tire production, including tire recycling, sustainable.

Extracting high-quality secondary raw materials

Under the umbrella of the Zeppelin Sustainable Tire Alliance, which was founded in March 2023, international partners work together along the value chain in the rubber and tire sector.

From mechanical recycling to feedstock recycling and the cleaning and refining of recyclates to increase the quantity of high-quality secondary raw materials, the aim is to close the loop for the recovery of valuable raw materials and to use high-quality recycled materials to produce new tires.

Eight marketing, technology, and process partners are currently members of the technology alliance. One of these partners is the Polish Recykl Group, which worked with Zeppelin Systems to commercialize develop a patented recycling solution for textile fibers in end-of-life tires.

What to do with the textile fibers in end-of-life tires?

The Polish company Recykl Organizacja Odzysku S.A. is part of the large group of companies Recykl Group (GRC) and has been working intensively on the reprocessing of end-of-life tires since 2004.

The company processes over 120,000 metric tons of used tire material every year, making it one of the largest enterprises of its kind in Central and Eastern Europe.

It has developed an innovative product from leftover textile fibers from end-of-life tires: the additive that goes by the brand name SMAPOL. This stabilizes and reinforces the asphalt binder and the structure of asphalt mixes to obtain homogeneous and durable road pavements.

The raw material for the production of SMAPOL comes from the high-quality textile fibers arising during the mechanical crushing of used tires. The multi-fiber mix of polyester, polyamide, aramid, and viscose fibers are activated, modified and compressed.

The procedure developed is a multi-stage mechanical cleaning and compaction process supported by surfactants and other additives.

Among other things, the development work focused on the end product’s bulk density, long term storage, resistance to weather conditions and ability to create homogenous asphalt mixes so that customers can rely on standardized product characteristics and consistent quality. This has also been tested and confirmed by TÜV, SGS and the Polish National Technical Assessment for construction products.

Industrial production of asphalt

Application of the product is simple: SMAPOL is produced in the form of pellets, which are delivered directly to production facilities in the asphalt industry in big-bags.

The proportion of SMAPOL is between two and six kilograms per metric ton of asphalt mix, depending on the properties of the bitumen used, the grain size of the aggregates and required properties of the asphalt pavements. Dosing generally takes place during asphalt production directly from the big-bags using pneumatic dosing systems or screw conveyors.

A Recykl production plant in Che?m, Poland, currently produces 500 kg of SMAPOL per hour. The product boasts impressive characteristics in terms of its workability and performance.

The pellets are a direct substitute for cellulose-based stabilizers, which are widely used for SMA asphalt mixes. The product is incorporated into the asphalt mix in the same way as cellulose-based stabilizers.

This means no changes are required in the asphalt mixes production process. At the same time, unlike cellulose-based additives, SMAPOL is a universal additive and can be used to improve the properties of all types of asphalt mixes. 

During the refinement of the SMAPOL production process, care was taken to ensure that it integrates seamlessly into existing recycling facilities. The system covers an area of approximately 80 m² and can be operated independently or integrated into existing recycling facilities. The Zeppelin design of the SMAPOL-line encompasses the production capacity of up to 1000 kg/h of SMAPOL additive.

SMAPOL makes roads safe

The development of the innovative additive SMAPOL has not only closed the loop in the processing of end-of-life tires, it has also created a useful way of recycling a residual material. In practice on the roads, it has further advantages over cellulose-based stabilizers, which have been widely used in road construction up until now.

Although the previously used products are good stabilizers for SMA asphalt mixes, they do not provide any significant mechanical reinforcement effects within asphalt pavement, for example regarding water ingress, fatigue, thermal cracking and rutting. By contrast, SMAPOL creates a new structure of asphalt mix, harnessing the advantages of the different types of synthetic fibers.

Studies have shown that road pavements, for example, made of Stone Mastic Asphalt (SMA) modified with SMAPOL are characterized not only by higher structural uniformity, but also by higher resistance to rutting, thermal cracking, and fatigue. Compared to stabilizing additives based on cellulose fibers, an optimal degree of bitumen absorption is reached.

This makes it possible to achieve not only higher strength and deformability indicators with a lower bitumen content, but also higher indicators for water and frost resistance (including corrosion resistance).

Cost Reduction through CO2 Transparency

CO2 taxes, CO2 certificates, and many other aspects have been brought to our attention once again, not least due to recent decisions by the federal government. These affect all of us, both in our private lives and in the business environment.

Therefore, it is essential to ensure the best possible transparency of the Product Carbon Footprint (PCF) right from the start when developing a new product like SMAPOL. Up to 90 percent of CO2 emissions do not occur in the actual production process but along the supply chain.

However, it is crucial to demonstrate, especially in recycling, how the use of waste materials positively impacts the overall energy balance compared to the exclusive use of new materials. Nevertheless, capturing the entire PCF seamlessly can be challenging at times.

The Emissions Management system SiGREEN aims to help overcome this challenge by creating data interfaces to all suppliers, thus providing verifiable transparency. Enriched by the CO2 consumption in the plant designed by Zeppelin Systems during the SMAPOL manufacturing process, Recykl can provide its customers with batch-specific evidence of the PCF of this batch, offering them a financial advantage.

Siemens-developed software SiGREEN is already successfully used in the automotive industry today. Its implementation in the CO2-intensive tire industry is planned.

Summary and outlook

SMAPOL closes the last gap in the recycling process for end-of-life tires. The textile fiber portion, which lacked a sensible and sustainable use in the past, can now be employed as a stabilizer and reinforcing additive for asphalt mixes of different types.

In such applications, it demonstrates impressive increases in resistance to weather influences and mechanical loads. Leading road construction companies have been closely involved in SMAPOL’s development. Everything is therefore in place for its use in road pavements on highways, city streets, and driveways, at airports or even in parking lots in all road climate zones.