End-of-life Tires Research Articles

Overview of the Effective Utilization of End of Life Tyres (ELTs) and Initiatives to “Reduce”

Overview of the Effective Utilization of End of Life Tyres (ELTs) and Initiatives to “Reduce”

Emerging investigator series: in-depth chemical profiling of tire and artificial turf crumb rubber: aging, transformation products, and transport pathways.

Crumb rubber generated from end-of-life tires (ELTs) poses a threat to environmental and human health based on its widespread use. Of particular concern is the use of ELT crumb rubber as infill for artificial turf fields, as people are unknowingly exposed to complex mixtures of chemicals when playing on these fields. Additionally, there is concern regarding transport of rubber-related chemicals from artificial turf into the environment. However, existing knowledge does not fully elucidate the chemical profile, transformation products, and transport pathways of artificial turf crumb rubber across different ages. To address these knowledge gaps, we utilized a multi-faceted approach that consisted of targeted quantitation, chemical profiling, and suspect screening via ultra-high performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS). We collected and processed 3 tire and 11 artificial turf crumb rubber samples via solvent extraction, leaching, and a bioaccessibility-based extraction. Nineteen rubber-derived chemicals were quantified using parallel reaction monitoring and isotope dilution techniques. In solvent extracts, the most abundant analytes were 1,3-diphenylguanidine (0.18-1200 μg g-1), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD, 0.16-720 μg g-1), 2-mercaptobenzothiazole (0.47-140 μg g-1), and benzothiazole (0.84-150 μg g-1). Chemical profiling assessed changes in sample diversity, abundance, polarity, and molecular mass. Suspect screening identified 81 compounds with different confidence levels (16 at level 1, 53 with level 2, 7 at level 3, and 5 at level 4). The formation rate of transformation products and clustering analysis results identified time-based trends in artificial turf field samples. We found that the first two years of aging may be critical for the potential environmental impact of artificial turf fields. Our analysis provides insight into the chemical complexity of artificial turf crumb rubber samples ranging from 0-14 years in age.

Study of the Viscoelastic and Rheological Properties of Rubber-Bitumen Binders Obtained from Rubber Waste.

According to scientific research from different countries, crumb rubber obtained from end-of-life tires (ELT) during processing can improve the properties of the asphalt mixture, thereby extending the service life of the road surface. This paper presents the modification of bitumen with industrial rubber waste. The modification of bitumen for roads is considered one of the most suitable and popular approaches. This research paper describes the details of using different types of crumb rubber as bitumen modifiers. The modified bitumen's main physical and mechanical characteristics were determined after conventional tests: penetration and ductility, softening point, and Fraas brittleness point. In order to obtain a rubber-asphalt concrete mixture with improved performance characteristics, the viscoelastic and rheological properties of rubber-bitumen binders and their comparison with polymer-bitumen binders were also studied. The research results show that with increasing temperature, the values of viscosity, shear stress and complex shear modulus of all studied bitumen systems decrease, the values of the phase shift angle increase, and the size of the rubber particles has a greater influence on the properties of bitumen systems.

Sustainable management of EOL tyres: A remanufacturing supply chain network design

End-of-life (EOL) objects such as tyres have been categorised as hazardous to the environment due to heavy metals and chemicals. To manage the recovery and remanufacturing operations of these EOL items, an effective network design is necessary. In this paper, we developed a mixed integer linear programming (MILP) model to minimize the total cost of the proposed EOL tyre remanufacturing supply chain network. Since, the problem is Non-deterministic Polynomial time hardness (NP-hard) in nature, we propose a prediction model that evaluates the operational feasibility of vehicle allocation and an evolutionary algorithm-based technique is employed to identify optimal facility locations, material flows among facilities, and demand distribution to individual automobiles for near-optimal solutions. Numerical experiments were conducted on a leading tyre remanufacturing company as a case study, and the results were compared with several evolutionary algorithms found that the Modified Genetic Algorithm (MGA) outperforms other algorithms. We demonstrate how, in each case, an optimal cost-effective location for a factory is found based on the cost and demand of the products. The study findings can assist governments and industry stakeholders in developing successful EOL tyre management strategies.

Recent advances on waste tires: bibliometric analysis, processes, and waste management approaches.

End of life tires (ELTs) are a pressing environmental concern due to their non-biodegradable nature and potential release of toxic chemicals, as confirmed by human health exposure studies. The expanding transport sector, driven by the automotive industry, has led to inadequate attention to safe tire disposal. This review extracted papers using keywords such as "waste tire rubber," "waste tire pollution," and "waste tire applications" from 2012 to 2023. Recycling publications have surged by 80% in the past decade, with China and the USA leading the research. Pyrolysis and devulcanization methods have emerged as key circular economy (CE) advancements, producing fuel and reusable rubber. Globally, 1.5 billion waste tires accumulate yearly, projected to increase by 70% in the next 30years if unaddressed. Around 26 million tonnes of used tires are generated annually worldwide, while civil engineering and backfilling use 17 million tonnes of recycled rubber particles. These tires are complex polymer composites, primarily composed of natural and synthetic rubber. The amorphous nature of rubber results in a 50% loss of mechanical properties when exposed to chemicals and microbes, shortening its lifespan. This paper explores the applicability of waste tire rubber and polymer fabrication to offer eco-friendly and cost-effective solutions for proper disposal, mitigating environmental accumulation.

Surface Activated Pyrolytic Carbon Black: A Dual Functional Sustainable Filler for Natural Rubber Composites.

The significant rise in end-of-life tires (ELTs) globally poses immediate environmental and human health risks. Therefore, to promote ELTs recycling and to reduce tire industry carbon emissions, herein we present a facile approach for fine-tuning the interfacial interactions between pyrolytic carbon black (P-CB) obtained from ELTs and natural rubber (NR) matrix using phosphonium-based ionic liquid (PIL). The reinforcing effect of PIL-activated P-CB was studied by replacing the furnace-grade carbon black (N330-CB) with varying PIL and P-CB loadings. Adding PIL improved the filler dispersion and the cross-linking kinetics with a substantially reduced zinc oxide (ZnO) loading. Considering the cross-linking and viscoelastic properties, it was concluded that the composite, P-CB/N330-CB-PIL (1.5)+ZnO (1) with half substitution of N330-CB with P-CB synergistically works with 1.5 phr PIL and 1 phr of ZnO resulting in improved dynamic-mechanical properties with a minimal loss tangent value at 60 °C (tanδ=0.0689) and improved glass transition temperature (Tg =-38 °C) compared to control composite. The significant drop (~29 % lower) in tanδ could reduce fuel consumption and related CO2 emissions. We envisage that this strategy opens an essential avenue for "Green Tire Technology" towards the substantial pollution abatement from ELTs and reduces the toxic ZnO.

A comparative life cycle assessment of tyre recycling using pyrolysis compared to conventional end-of-life pathways

End-of-life tyres (ELTs) are difficult to recycle due to their complex composition. Although there are several possible pathways to manage ELTs, in Germany roughly 50 % of the ELTs are still incinerated. One emerging technology that promises recycling of ELTs is the thermochemical processing through pyrolysis. This technology enables to recover carbon black and pyrolysis oil that can be reused for new tyres. Therefore, this study presents a comprehensive life cycle assessment to compare the environmental impacts from pyrolysis of ELTs against current dominant alternative end-of-life treatment pathways. The investigated alternative end-of-life pathways are (i) incineration in a cement plant, (ii) incineration in a dedicated incineration plant, and (iii) production of infills for artificial turfs. The results show that the recycling of ELTs for material recovery has lower environmental impacts in the categories global warming, particulate matter and resource use compared to end-of-life pathways that target energy recovery.

Design and operation of a packed pilot scale distillation column for tire pyrolysis oil: Towards the recovery of value-added raw materials

This work describes the key features involved in the design and operation of a pilot scale distillation column for the recovery of value-added products from tire pyrolysis oil (TPO), as part of the BLACKCYCLE project. The distillation unit was designed using engineering heuristic rules, simulated distillation (SimDist) data and Aspen Hysys ® modeling. The distillation plant consists of a packed column with a nominal throughput of 20 kg/h, and is classified at the fifth technology readiness level (TRL-5). The commissioning and results of long-term experimental campaigns for validation purposes are also presented. In this way, important information is gathered for the design of larger plants. The distillation unit was tested and validated using TPO produced from a pilot scale continuous single-auger pyrolysis plant. A first distillation was performed yielding a heavy fraction (HF-1) with properties suitable for carbon black production, while the light fraction (LF-1) includes the presence of value-added chemicals such as benzene, toluene, ethylbenzene and xylenes (BTEX) and limonene. The LF-1 was also used for a second distillation, producing a stream high in limonene at the bottom (HF-2), and another one high in BTEX compounds at the top (LF-2), which are valuable raw materials for polymer production and petrochemicals, respectively. The key results obtained here are expected to provide an outstanding impetus for the circular economy of complex streams such as end-of-life tires (ELTs) by combining pyrolysis and distillation technologies.

Enhanced monoaromatic hydrocarbons production via pressurized catalytic pyrolysis of end-of-life tires

One of the most active research lines in the area of end-of-life tires (ELT) recycling is pyrolysis, which consists of a thermal decomposition at moderate temperatures and in absence of oxygen. This process was initially focused on the recovery of carbon black and energy, this last by combustion of both the gas and liquid fractions obtained. However, its rentability and alignment to the circular economy goals would be improved if added-valuable chemicals were produced from the pyrolytic oil. For this purpose, the application of catalysts (catalytic pyrolysis) and modification of some operation conditions have been approached in previous works. However, pressure has been missed until now despite the important role it may play affecting the volatilization process, the vapors residence time and the pyrolytic compounds-catalyst contact. This work reports for first time a comprehensive study that demonstrates that carrying out catalytic pyrolysis under moderate pressure (10 bar) is very beneficial to improve the quality of the oil. Thermal and ex-situ catalytic pyrolysis have been performed in a fixed-bed reactor using a real scrap tire as feedstock. Both pressure and catalyst/tire ratio have been modified, using a nano-crystalline ZSM-5 zeolite as catalyst. Increasing the pressure from 1 to 10 bar leads to a slight reduction in the oil yield, which is somewhat more remarkable in the presence of catalyst. Nevertheless, the resulting pyrolysis oil was enriched in marketable monoaromatics (benzene, toluene, xylenes, ethylbenzenes and cymenes) due to a promotion of hydrogen transfer and aromatization reactions. In the case of pressurized catalytic tests, there was a drastic increase in the monoaromatic mass yields, reaching values up to 23–26 % and concentrations in the oil of 50–56 wt%. Finally, the feasibility to regenerate and reuse the catalyst by thermal treatment has been also approached, observing minor changes in its structural and activity properties.

Sustainable use of End-of-Life-Tires (ELTs) in a vibration isolation system

Huge stockpiles of End-of-Life Tires (ELTs) are of major global concern. This paper investigates and helps to demonstrate the beneficial utilization of ELTs to provide geotechnical seismic isolation (GSI) of machine foundations located on a rubber-soil mixture (RSM). A series of laboratory tests is conducted to extend the understanding of RSM behavior beyond that previously elaborated, particularly by demonstrating the efficiency of the GSI-RSM system and by defining its optimal parametric values. The results indicate that increasing the thickness of the RSM layer and soil cap, along with the addition of rubber content, up to the optimum values lead to enhanced performance. Beyond these optimum values, the benefits start to decrease. For the determined optimum rubber content (8%), RSM layer thickness (0.1B), and soil cap thickness (0.15B) at a vibration moment level of 0.17 N.m, the GSI-RSM system achieves maximum reductions of 36%, 43%, and 77% in resonant frequency, resonant displacement, and resonant acceleration, respectively, compared to untreated beds. Moreover, the GSI-RSM system effectively reduces the developed peak particle velocity (PPV) and kinetic energy, independent of the excitation frequency. The increased damping and significant energy dissipation demonstrates the system’s effectiveness in mitigating vibrations. This environmentally-friendly technique presents a low-cost alternative for improving the vibration behavior of soil beds. It provides the basis for the wider adoption of ELTs for GSI, for machine foundations and for other infrastructure projects with similar soil vibration concerns, including building foundations, transportation infrastructure and industrial facilities. In this way the research contributes to the growing body of sustainable practices in the construction industry.

Pollution Effect Of Painted End-Of-Life Tires On Water Resources: Case Study Of Landscape Applications

Reuse of End-of-Life Tires (ELT), especially in architectural applications or landscape areas, is highly preferred today. At the same time, waste tires are used to prevent collisions on the side surfaces of boats in recreational areas such as lakes. Being able to be painted in the desired color for open space design is also a great advantage for quality and cost-effective projects. However, some toxic pollutants can also be released by leaching from whole, wrinkled or granular ELT-based products. In this study research conducted on acrylic spray-painted whole size ELT to evaluate general leaching characteristics under two different water sources. The small variety found for pH in both experimental conditions (0.10 to 0.24 for lake water and 0.17 to 0.40 for ornamental pool water). The electrical conductivity (EC), Total Dissolved Solid (TDS) and Salinity were found to be constantly increases as soaking continue for both type of water. However, the highest EC value of 585 μs, TDS value of 430 ppm and Salinity value of 0.30 ppt were observed with ornamental pool water treatment conditions. A similar trend was also observed for turbidity, as leaching in progress which is continuously increased. It is reasonable to hypothesized that landscape applications (ornamental pool, landscape pool or parks) water is potentially more aging effects on acrylic painted ELT rather than lake water. As a result, the reuse of painted ELT's in open recreation areas, boats on the lake and parks will increase the risk of pollution of water resources.

Blends Comprised Waste Tires and Reinforcing Carbon Black: Effect of Mixing Sequence on Processing and Physical Properties

In this study, a simple recycling strategy for End-of-Life Tires (ELT) was described. The direct incorporation of a large-sized Ground Tire Rubber (GTR) as a major dispersed phase into the elastomer matrix was assisted by the promoter-induced mixing, which canceled the cost-consuming reclaiming step. A macro-dispersion of GTR in the mix was assessed via a surface roughness extent. This method allowed us to predict the behavior of the rubber compound. A nonuniform rough surface while the master step was converted to a smooth roll-processed web after re-milling. The processing steps were correlated with the fragmentation of GTR, partial interfacial adhesion, restoration of tack, and unsaturation. The sequential mixing generated a reasonable level of viscosity, building tack, and green strength. The structural integrity of the re-vulcanizates was provided with a higher curing temperature and was confirmed by the improved abrasion and tear resistance, retention of heat build-up, storage moduli values, and lower standard deviation compared to the unmodified GTR and neat NR/BR blends. The developed compounding and co-curing steps exhibit a practical way of GTR recycling using the standard mixer with lower operational and compound expenses, and the absence of toxic gas release.

Pursuing the End-of-Life Tire Circularity: An Outlook toward the Production of Secondary Raw Materials from Tire Pyrolysis Oil

Pyrolysis is perceived as the missing link between the management of end-of-life tires (ELTs) and the tire industry because it strikes directly in the transition from a linear to a circular economy model and toward the defossilization of diverse economic sectors. Tire pyrolysis oil (TPO) is one of the most valuable and interesting fractions derived from the pyrolysis of ELTs. It contains valuable chemicals including, among others, benzene, toluene, ethylbenzene, and xylene, as well as limonene, which are some of the building blocks of the petrochemical industry. Within the circular economy framework, traditional practices such as the direct use of TPO in combustion systems seem to exhibit a low circularity degree. Instead, the production of secondary raw materials that can be reused for multiple purposes associated with the petrochemical industry is getting special attention. Based on the above, this work aims at reviewing different pathways currently explored in the scientific community to produce various value-added products from TPO. Due to the similarity of its properties with those of petroleum streams, the coprocessing of TPO using existing units in conventional refineries exhibits a massive potential. In this manner, the properties of the derived products can be fine-tuned according to the hydrocarbons and petrochemical market requirements. As such, discussed are the advantages, recent progress, and challenges in the implementation of conventional refinery practices such as distillation, fluid catalytic cracking (FCC), hydroprocessing, and steam cracking for TPO post-treatment. These processes are seen as the path to integrate TPO in the current hydrocarbon/petrochemical market.

New lightened plaster material with dissolved recycled expanded polystyrene and end-of-life tyres fibres for building prefabricated industry

The overexploitation of natural resources and the shortage of labour in the building sector is encouraging the development of prefabrication applied to building. This is leading the agents involved in construction to increasingly opt for the application of prefabricated systems that optimise resources while shortening construction execution times. Thus, the main objective of this research is the development of a new lightweight construction material composed of plaster, in which the conglomerate has been partially replaced by dissolved expanded polystyrene (EPS) waste and the addition of textile fibres from end-of-life tyres (ELT). The results obtained after the physicochemical and mechanical characterisation of the new plaster composite show how a 31.3% lighter material is obtained, with a 66.7% lower thermal conductivity and a 33.3% higher flexural strength in plates compared to traditional gypsum material. This improvement in the technical performance of the composites produced, combined with the reduction in the consumption of natural resources and the large amount of waste recovered and reintroduced into the production process, confirm the suitability of the new construction material developed for use in the production of more sustainable prefabricated plates and panels.

The potential effect of crumb rubber on the maximum sound absorption performance of asphalt mixtures

In this research, several types of asphalt mixtures with the addition of crumb rubber (CR) from end-of-life tires (ELT) have been studied. The volumetric characteristics, texture surface and sound absorption (impedance tunnel) of the asphalt mixtures were analyzed in the laboratory. Based on the results obtained, a model for predicting sound absorption as a function of the volumetric characteristic and surface texture of the mixtures was proposed. It has been observed that the parameter that most strongly governs the sound absorption of the bituminous mixture is its void content. CR can moderately improve the sound absorption, especially in mixes with a high void content.

Neutrosophic CEBOM-MACONT model for sustainable management of end-of-life tires

Management of end-of-life tires (ELTs) has evolved into an important sustainability requirement that should follow circular economy principles. It is increasingly important to find environmentally-friendly and cost-effective solutions for ELT management, particularly in the context of large freight transportation companies. Selecting the most sustainable solution from the set of available ELT management strategies, such as retreading, recycling, energy recovery, and landfilling, presents a decision-making challenge for authorities. This study aims to introduce a practical evaluation framework comprised of strategy alternatives and key decision-making criteria to support transportation companies in managing ELT flows. Also, the research introduces an advanced two-stage neutrosophic decision support model to solve the addressed problem and reveal the most sustainable strategy. The model is based on the integration of the cross-entropy-based optimization model (CEBOM) method and mixed aggregation by comprehensive normalization technique (MACONT) under the type-2 neutrosophic number (T2NN) environment. Prominent features of T2NN-CEBOM are hybrid weighting sub-framework and processing controllability. Distinguished characteristics of T2NN-MACONT are average referencing, triple-normalization support, modeling of risk attitude behavior, adjustable ordering schemes, and an advanced scoring system. The real-life study of one of the largest German freight transportation companies that operates along an important European transit route offers practical insights for decision-makers when evaluating ELT management strategies. The research findings show that retreading is the most sustainable solution. The eight sensitivity analyses confirm the high robustness of the introduced decision-support model. The comparative analysis reveals the superiority of T2NN-CEBOM-MACONT for employment in practical settings.

Ground Tire Rubber Particles as Substitute for Calcium Carbonate in an EPDM Sealing Compound.

Ground tire rubber (GTR) is a product obtained by grinding worn tire treads before retreading them or via the cryogenic or ambient temperature milling of end-of-life tires (ELTs). The aim of this study is to evaluate if calcium carbonate can be substituted by GTR and, if so, to what extent. Different types of ground tire rubber are incorporated in an EPDM (ethylene-propylene-diene-rubber) model compound as partial or complete substitutes of calcium carbonate. The raw compounds and the vulcanizates are characterized to identify the limits. In general, it is apparent that increasing amounts of GTR and larger particles degrade the mechanical properties. The GTR also influences the vulcanization kinetics by reducing the scorch time up to 50% and vulcanization time up to nearly 80%. This is significant for production processes. The compounds with one-third substitution with the smaller-particle-size GTR show mostly similar or even better properties than the reference.

Effect of a New Additive Based on Textile Fibres from End-of-Life Tyres (ELT) on the Mechanical Properties of Stone Mastic Asphalt

Stone Mastic Asphalts (SMA) are asphalt mixes with discontinuous granulometry and a high content of asphalt binder. In order to prevent draindown of the asphalt binder and ensure good performance, these mixes must be strengthened with cellulose or mineral fibres and/or polymer additives. This study was designed to evaluate the effect of a granular additive based on waste tyre textile fibres (WTTF), developed as a replacement for cellulose commercial additives in SMA mixes. Use of the WTTF-based additive will encourage the development of sustainable mixes by recycling a by-product of end-of-life tyres (ELT), which currently constitute a major environmental problem around the world. To this end, in the present experimental study we evaluated the replacement of cellulose-based commercial fibre with different percentages of WTTF-based additive (0%, 50%, 75%, 100%) in an SMA asphalt mix. The following design and performance properties were evaluated: resistance to cracking, stiffness modulus, sensitivity to moisture, and resistance to permanent deformation. The results indicated that replacing 100% of the cellulose commercial additive in the SMA mix by the WTTF-based additive allowed the mix to meet its design properties and showed good performance in the mechanical properties evaluated, with behaviour similar to that of the reference SMA mix.

Design of Reverse Logistics Network for Waste Tire Incineration in Cement Factories

This study focuses on recovery options for end-of-life tires (ELTs). One of the most proper recovery options for ELTs is incineration of them in cement plants. There are 49 integrated cement factories which have Environmental Permit and License Certificate in Turkey as the final processing plant. Besides benefits of recovering ELTs to environment, cost aspect of process is crucial. In this study, logistic network design of waste tires sent from collection points to these factories to minimize the costs involved is planned. There are three echelons of supply chain as waste tires collection point, contractor firms and cement factories. Model for this network considers transshipment plan of waste tires between the echelons of supply chain and routes used to gather them. Model that deal with this system are expressed as mixed integer linear programming (MILP) problem. As a case study, model verified with data’s for Ankara

A circular system for end-of-life tires under extended producer responsibility

ABSTRACT This paper presents a circular recycling system for end-of-life tires (ELTs) under extended producer responsibility (EPR) by integrating Individual Producer Responsibility (IPR) and Industrial Symbiosis (IS). The system aims for sustainability and circularity in the tire industry, avoiding the detrimental effects of landfilling. It focuses on emission-free recyclers to create IS for ensuring environmental sustainability. Additionally, the system uses a “dynamic pricing strategy” to take-back ELTs from consumers. This paper also presents a “multi-period scenario-based nonlinear mixed integer programming” model to investigate the economic sustainability of the proposed system under uncertainty. Three different evolutionary metaheuristic algorithms, “genetic algorithm (GA)-based simulated annealing”, “GA” and a new variant of “particle swarm optimization” are used to obtain the solution of the model. Through a case study, it is found that the proposed system is economically sustainable and has the potential to aid in the successful implementation of EPR in the tire industry.