Ground Tire Rubber Research Articles

Simultaneous devulcanization and denitrification: a novel approach for valorization of both ground tire rubber and nitrate-containing wastewater.

This study focused on a new approach for valorization of both ground tire rubber (GTR) and nitrate-containing wastewater via simultaneous devulcanization and denitrification. Initially, sulfur-based autotrophic denitrifiers were successfully enriched from three different seed sludge sources, biological nutrient removal (BNR) sludge, anaerobic digester sludge and BNR sludge of a leather organized industrial zone WWTP. Average nitrate removal efficiencies were 96-98%. Biological devulcanization (biodevulcanization) of GTR was later investigated with these enriched cultures. Results revealed that biodevulcanization was only achieved with the culture enriched from BNR sludge of the leather organized industrial zone WWTP, as 3.9% sulfur removal (desulfurization efficiency). Metal sulfate precipitation was speculated to cause an underestimation of the desulfurization ratio. Fourier-transform infrared spectroscopy (FTIR) results demonstrated a decrease in the intensity of the C-S bonds and an increase in intensity of S-O bonds in treated GTR samples. This was attributed to the oxidation of sulfidic crosslinks, i.e. verification of biodevulcanization. This study indicated that simultaneous biodevulcanization and denitrification could be a promising process for valorization of both GTR and nitrate-containing wastewater which in turn would support circular economy and sustainable development.

Analyzing Thermal Degradation Effects on Devulcanized GTR-Based NR/SBR/NBR Rubber Compounds Reinforced with SiO2 Particles

The large number of tires produced annually demands new recycling methods. A key challenge associated with recycling elastomers is their crosslinking structure that prevents fusion. It is possible to reverse crosslinking through a process called devulcanization. Devulcanized elastomers can be blended with fresh rubber and revulcanized for reuse. This paper examines samples made from natural rubber (NR), styrene–butadiene rubber (SBR), and nitrile butadiene rubber (NBR), blended with varying proportions of devulcanized ground tire rubber (dGTR) and newly revulcanized rubber. SiO2, commonly present in tire formulations, is also added. Samples of these materials, with 0, 10, 20, and 40 phr of dGTR are subjected to accelerated degradation for 0, 30, 60, 120, and 240 h. The effects of this treatment, the influence of SiO2, and the presence of a silane-based devulcanization agent (TESPT) that promotes the interaction between the rubber and silica, are analyzed at the microstructural level (FTIR, TGA, SEM) and through mechanical properties testing. The microstructural results of the spectroscopy and thermal analysis show that interactions between dGTR, silica, and silane compounds form aggregates that impact the material properties and degradation of the tires. Mechanically, when the sample contained up to 20 phr of dGTR, the compound presented a more brittle behavior, due to the crosslinking induced by the degradation.

Devulcanization of ground tire rubber using a plasma-assisted fluidized-bed system

The disposal of ground tire rubber (GTR) poses a significant environmental threat, necessitating the development of sustainable regeneration strategies. As an attractive alternative to traditional recycling techniques, plasma-based method is being actively explored for GTR devulcanization. To address the critical issue of poor contact between rubber and reactive species in plasma fixed-bed reactor, a novel plasma fluidized-bed system based on wire-cylinder configuration is designed and employed to regenerate GTR in this work. The results demonstrate that plasma treatment effectively breaks C-S and S-S bonds within the rubber matrix, indicative of partial de-crosslinking of the network structure. This structural alteration is manifested in a decreased crosslinking density, facilitating the partial restoration of flowability in the regenerated GTR. Notably, after 30 min of plasma treatment, the tensile strength of regenerated rubber increased significantly from 6.4 MPa to 9.4 MPa, and the elongation at break rose from 362 % to 390 %, thereby satisfying the performance requirements of superior-grade rubber materials. An underlying plasma devulcanization mechanism is proposed through a comprehensive analysis that integrates both experimental data and characterization results. The developed plasma fluidized-bed system offers an eco-friendly method for GTR devulcanization, holding significant potential to contribute to environmental sustainability and bolster circular economy efforts.

The Input of Nanoclays to the Synergistic Flammability Reduction in Flexible Foamed Polyurethane/Ground Tire Rubber Composites.

Currently, postulated trends and law regulations tend to direct polymer technology toward sustainability and environmentally friendly solutions. These approaches are expressed by keeping materials in a loop aimed at the circular economy and by reducing the environmental burdens related to the production and use of polymers and polymer-based materials. The application of recycled or waste-based materials often deals efficiently with the first issue but at the expense of the final products' performance, which requires various additives, often synthetic and petroleum-based, with limited sustainability. Therefore, a significant portion of research is often required to address the drawbacks induced by the application of secondary raw materials. Herein, the presented study aimed to investigate the fire performance of polymer composites containing highly flammable matrix polyurethane (PU) foam and filler ground tire rubber (GTR) originating from car tire recycling. Due to the nature of both phases and potential applications in the construction and building or automotive sectors, the flammability of these composites should be reduced. Nevertheless, this issue has hardly been analyzed in literature and dominantly in our previous works. Herein, the presented work provided the next step and investigated the input of nanoclays to the synergistic flammability reduction in flexible, foamed PU/GTR composites. Hybrid compositions of organophosphorus FRs with expandable graphite (EG) in varying proportions and with the addition of surface-modified nanoclays were examined. Changes in the parameters obtained during cone calorimeter tests were determined, discussed, and evaluated with the fire performance index and flame retardancy index, two parameters whose goal is to quantify the overall fire performance of polymer-based materials.

The preparation of different types of reclaimed rubber and their applications in tire inner liner

AbstractIn this work, the application of reclaimed ground tire rubber (RGTR) and butyl reclaimed rubber (BRR) in the inner liner rubber were investigated. Carbon black dispersion, rheological, mechanical, tear strength, dynamic compression heat build‐up, aging performance, and gas barrier properties of tire inner liner were evaluated to analyze the effects of reclaimed rubbers on the tire application. It was found that RGTR improves carbon black dispersion and tear strength of tire inner liner, while maintaining comparable tensile strength, particularly with low amount of RGTR. Furthermore, compounds containing lower amounts of RGTR exhibit reduced heat build‐up during dynamic compression tests. Additionally, RGTR with higher reclamation degree demonstrates favorable aging performance, and has superior gas barrier properties at lower amount. These findings suggest promising opportunities for the application of reclaimed rubber to enhance the performance inner liner of Radial Engineering Tires and contribute to the waste management.

The Influence of Devulcanization and Revulcanization on Sulfur Cross-Link Type/Rank: Recycling of Ground Tire Rubber.

Devulcanized rubber could be a valuable material feedstock to help in the manufacture of sustainable rubber products. However, the differences in the chemistry and structure of devulcanized rubber have limited industrial uptake. This work demonstrates how devulcanization affects the concentration and ratios of mono-, di-, and polysulfidic cross-links. These residual cross-links make devulcanized rubber chemically dissimilar from virgin rubber, affecting (re)vulcanization. The hypothesis that the sulfur rank of revulcanized material can be modified by the sulfur/accelerator ratio was evaluated by two different cure packages. Despite substantial differences in the accelerator/sulfur ratio, both recycled rubber compounds favored the formation of polysulfidic cross-links.

Tensile and Elastocaloric Properties of Natural/Devulcanized Waste Rubber Blends.

The need for eco-friendly cooling materials and material recycling are two urgent challenges to address. In this paper, the role of the ground tyre rubber treatment (cryo-grinding and devulcanization) is investigated on the tensile and elastocaloric properties of Natural rubber (NR)/ ground tyre rubber (GTR). The GTR particles that are sieved (<63µm) and devulcanized by microwave irradiation (1 min at 800Watts) exhibit a low network chain density (0.53 × 10-4mol.cm-3) resulting from crosslinks breakage and rubber chains scission, as supported by FTIR showing a decrease of S─S, C─S, and C─C bonds. The NR/GTR blends show a high elastocaloric effect as compared to the pristine NR, which can be ascribed to the high content of carbon black in the GTR (52wt.%) and also the high level of devulcanization of the GTR. NR/GTR blends reach a heating of +8°C and a cooling of >-6°C, resulting in a material's coefficient of performance COPmat = 2.8-3 compared to 2.6 for the pristine NR. The concomitant effect of cryogrinding and microwave devulcanization is proposed as a way to improve the tensile and elastocaloric properties of natural rubber/waste rubber blends for their possible integration into elastocaloric devices for heating/cooling applications.

Optimizing modified asphalt binder performance at high and intermediate temperatures using experimental and machine learning approaches

Asphalt pavements are highly susceptible to temperature-induced stresses, which can lead to significant deterioration such as rutting at high temperatures and cracking at low temperatures. These challenges are exacerbated by global warming, which raises pavement temperatures and potentially accelerates material degradation. Addressing these issues, this study utilizes two base asphalt binders, PG 64–22 and PG 76–22, and the use of phase change materials (PCMs) like styrene-butadiene-styrene, lignin, and ground tire rubber to enhance the resilience of asphalt binders. Through an extensive experimental investigation, which includes aging processes such as rolling thin film oven and pressure aging vessel, alongside a series of both traditional and advanced tests (including dynamic shear rheometer, rotational viscometer, Fourier transform infrared spectroscopy, among others), a comprehensive set of 51 samples were analysed. By incorporating these binders and PCMs into asphalt, the experimental work demonstrated a significant improvement in the thermal and mechanical properties, effectively increasing resistance to high-temperature rutting and fatigue cracking. Complementing the experimental approach, machine learning models were employed to predict complex asphalt binder properties, such as combustion value and failure temperature, based on the experimental data. This dual approach fills a significant gap in the literature by offering a more efficient method and prediction model for optimizing pavement materials amidst climate change, while also promising to significantly advance pavement technology by enhancing material design and performance.

Molecular dynamics simulation of interfacial interaction mechanisms between ground tire rubber and styrene-butadiene rubber enhanced by nanomaterial incorporation

The recycling of ground tire rubber (GTR) is an effective method for addressing black pollution. In this study, we investigated and compared the effects of acidic oxidation treatments and different nanomaterial contents on the interfacial properties of styrene-butadiene rubber (SBR) and GTR. Molecular models of GTR modified by acidic oxidation and nanomaterials, as well as SBR, were established. The interfacial interaction mechanisms between SBR and GTR were studied through tensile and shear behaviors. The results indicated that the properties of SBR-GTR interface were enhanced through acidic oxidation and nanomaterial modification, with the latter demonstrating superior advantages in augmenting the interfacial strength. Specifically, the addition of a carbon nanotube and graphene increased the interfacial cohesion strength by 55.12 % and 82.93 %, and the interfacial shear strength by 29.87 % and 43.05 %, respectively. Moreover, graphene exhibited superior performance in enhancing interfacial interactions compared to carbon nanotubes and increasing the nanomaterial content did not positively impact the improvement of interfacial properties. The interfacial properties of SBR and GTR were quantitatively analyzed using molecular dynamic (MD) simulations. This study provides a theoretical foundation for enhancing the mechanical properties of recycled rubber by using nanomaterials, thereby guiding the experimental preparation of recycled rubber.

Thermomechanical-chemical devulcanization of ground tire rubber

Abstract We developed a thermomechanical devulcanization process of ground tire rubber (GTR) by incorporating chemicals to achieve better devulcanization. The samples were devulcanized in a twin-screw extruder with the help of three types of chemicals that aid devulcanization: N-(cyclohexylthio) phthalimide (PVI), dibenzamid diphenyl disulfide (DBD) and dialkyl-pentasulfide (DPS, commercialized as Aktiplast 79). We characterized the resulting devulcanizates by Soxhlet-extraction, and produced vulcanized sheets, which we characterized mechanically and examined the vulcanization process. We found that all chemicals facilitated better devulcanization and the devulcanizate had a more rubber-like behavior during mixing. Vulcanization was also slightly improved and reversion was reduced. When revulcanized, the rubber had improved strain at break and tear strength.

Novel Design of Eco-Friendly High-Performance Thermoplastic Elastomer Based on Polyurethane and Ground Tire Rubber toward Upcycling of Waste Tires.

Waste rubber tires are an area of global concern in relation to reducing the consumption of petrochemical products and environmental pollution. Herein, eco-friendly high-performance thermoplastic polyurethane (PU) elastomers were successfully in-situ synthesized through the incorporation of ground tire rubber (GTR). The excellent wet-skid resistance of PU/GTR elastomer was achieved by using mixed polycaprolactone polyols with Mn = 1000 g/mol (PCL-1K) and PCL-2K as soft segments. More importantly, an efficient solution to balance the contradiction between dynamic heat build-up and wet-skid resistance in PU/GTR elastomers was that low heat build-up was realized through the limited friction between PU molecular chains, which was achieved with the help of the network structure formed from GTR particles uniformly distributed in the PU matrix. Impressively, the tanδ at 60 °C and the DIN abrasion volume (Δrel) of the optimal PU/GTR elastomer with 59.5% of PCL-1K and 5.0% of GTR were 0.03 and 38.5 mm3, respectively, which are significantly lower than the 0.12 and 158.32 mm3 for pure PU elastomer, indicating that the PU/GTR elastomer possesses extremely low rolling resistance and excellent wear resistance. Meanwhile, the tanδ at 0 °C of the above-mentioned PU/GTR elastomer was 0.92, which is higher than the 0.80 of pure PU elastomer, evidencing the high wet-skid resistance. To some extent, the as-prepared PU/GTR elastomer has effectively solved the "magic triangle" problem in the tire industry. Moreover, this novel research will be expected to make contributions in the upcycling of waste tires.

Sustainable thermoplastic elastomers based on thermoplastic polyurethane and ground tire rubber

AbstractIn this research, blends are prepared of thermoplastic polyurethane (TPU), ground tire rubber (GTR) and its devulcanized version (dGTR). The primary objective is to produce thermoplastic elastomers wherein TPU is partially substituted by GTR or dGTR obtained from used tires, thereby forming a blend with a favorable cost/value ratio and a smaller environmental footprint. Throughout the experiment, the rubber content of the blends is varied between 0 and 50 wt% and the effect on mechanical properties is investigated. The blends are compounded with a twin‐screw extruder, after which sheet samples are produced by injection molding. With a view to a possible future industrial application, it is important that both the compounding and the injection molding of the specimens are easy to perform, even with a 50 wt% filler content. Increasing the amount of rubber phase reduce the tensile strength and elongation at break of the blends. Unfortunately, devulcanization did not significantly improve the properties of the blends. Overall, even at a (d)GTR content of 50 wt%, an elongation at break of 300% is achieved, which allows the use of the blends as thermoplastic elastomers. In addition, dynamic tests show that the rubber phase increases the damping capacity of the samples.

Development of a sustainable polymer composite: enhancing properties of waste plastic with ground tire rubber reinforcement

The growing interest in utilizing waste for composite development has prompted investigations across social, economic, and environmental domains. This study focuses on utilizing recyclable waste plastic materials and micro-sized ground tire rubber (GTR) of varying sizes (600 μm, 300 μm, and 150 μm) to create a polymer matrix composite (PMC). Employing a thermal blending technique, the manufacturing process adjusts the composition ratios of polymer and GTR from 90:10 to 50:50. Subsequently, Energy Dispersive Spectroscopy (EDS) is utilized to analyze the PMC composition, while Fourier-transform infrared spectroscopy confirms functional group and chemical structure. The study demonstrates significant improvements in various properties upon adding GTR to High-Density Polyethylene (HDPE) and Low-Density Polyethylene (LDPE) composite materials. For HDPE-GTR composites, the melting temperature (Tm) ranged from 120.29 °C to 138.53 °C, crystallization temperature (Tc) from 102.84 °C to 127.14 °C, and enthalpy of melting (ΔHm) from 70.96 to 139.67 J g−1. Crystallinity (Xc) varied from 48.43% to 52.96%. In LDPE-GTR composites, Tm ranged from 106.08 °C to 129.57 °C, Tc from 90.27 °C to 112.20 °C, ΔHm from 75.59 to 142.53 J g−1, and Xc from 51.59% to 54.05%. Moreover, mechanical properties such as tensile strength, flexural modulus, and impact strength exhibited enhancements with GTR addition to the polymer matrix. These findings underscore the potential of sustainable waste utilization, advancing environmentally friendly and resource-efficient composite materials.

Recyclability and self-healing capability in reinforced ionic elastomers

This study presents a comparative analysis of different sustainable alternatives for producing reinforced ionic elastomers that are not just mechanically robust but also excellent in recyclability and self-healing, marking a significant advancement in sustainable materials science. Ionically crosslinked carboxylated nitrile rubber (XNBR) was combined with conventional (carbon black and silica) and sustainable (cellulose and ground tire rubber) fillers. The sustainable fillers not only enhanced the mechanical performance (reinforcing character) but also maintained high healing efficiencies (>80 %). Notably, the incorporation of just 10 phr of waste-based ground tire rubber (GTR) produced by water jet grinding (WJ-GTR) resulted in a material capable of complete repair and recycling (100 % efficiency) after temperature-driven protocols, with mechanical properties and a reinforcement index comparable to those of conventional fillers such as silica. This achievement represents a major breakthrough in the field of sustainable composites, as it offers a unique blend of robust mechanical properties and environmental sustainability.

Resurface of rubber modified asphalt mixture with stress absorbing membrane interlayer: From laboratory to field application

The increasing concern over tire pollution, exacerbated by the improper disposal of waste tires, serves as the backdrop for this research, which aims to explore the efficacy of incorporating ground tire rubber (GTR) into asphalt mixtures enhanced with a stress-absorbing membrane interlayer (SAMI). In this study, three variations of Hot Mix Asphalt (HMA) were evaluated: a conventional mix, a rubber-modified asphalt mixture (RMA), and a trans-polyoctenamer rubber (TOR) modified asphalt mixture in the laboratory. The assessment focused on the high and low-temperature performance of the asphalt mix and binder. Key findings from the laboratory tests indicate that the integration of a SAMI layer and GTR as additives markedly boosts the crack resistance of the asphalt mixture. Despite a reduction in fracture energy across all three HMA types following long-term aging, the GTR-modified HMA maintained superior fracture energy relative to the conventional mix. Initially, the inclusion of GTR adversely affected the mixture's rutting resistance. However, after undergoing long-term aging, both the conventional and GTR-modified HMAs exhibited exceptional rutting and moisture damage resistance. Field noise assessments further demonstrated that GTR-enhanced pavements produced noise levels approximately 2 dB lower than those of standard asphalt pavements. Additionally, pavements lacking a SAMI layer manifested low-severity cracking, with an average cracking frequency occurring every 2 ∼ 6 m, whereas pavements equipped with a SAMI layer exhibited no cracking following two winter seasons. The rubber asphalt overlay may increase the leaching of 6PPD-quinone, but the SAMI layer helps reduce tire wear particle generation by preventing road cracking. Rubber asphalt overlay leaching tests resulted in 6PPD-quinone concentrations lower than currently available toxicity data (LC50 for Coho Salmon, 0.095 ug/L). In conclusion, the utilization of dry-processed rubber asphalt mixes alongside a SAMI layer in pavement construction not only has the potential to extend the service life of pavements but also contributes to the production of quieter road surfaces. This study underscores the environmental and functional benefits of incorporating rubber modifications into asphalt pavements, presenting a viable strategy for mitigating tire pollution through the reuse of waste tires in infrastructure.

Green Composite Concrete Incorporating with Non-Biodegradable Wastes

This research studied the properties of the green composite concrete for paving blocks comprised of the non-biodegradable wastes of PET bottle flake (15-35 wt%), metalized plastic film from food packaging (0-5 wt%), colored glass powder (5-15 wt%), and ground tire rubber (5-20 wt%) as low cost and ecofriendly reinforced materials. The various concentrations of those wastes in the concrete can be grouped into 14 compositions. The properties of the composite paving blocks were compared to those of standard concrete in terms of density moisture absorption, water absorption, and compressive strength. The results showed that the standard paving blocks had better properties than those of composite paving blocks. The combination of colored glass powder in the concrete can enhance all properties of the concrete block; moreover, the insertion of scrap tires can improve moisture absorption property. However, the addition of metalized plastic, and plastic bottle wastes induced the void inside the concrete decreasing the properties of the concrete.

Assessment of Ground Tyre Rubber Impact on Stiffness Modulus and Cracking Resistance of Bituminous Mixtures

Abstract The objective of this study was to evaluate and characterize the performance of ground tire rubber (GTR) modified dense graded asphalt mixtures to recommend a suitable GTR content to produce a mix that provides superior pavement performance characteristics. The research effort encompassed investigation of stiffness and cracking resistance of six dense graded asphalt mixtures, including one conventional and five modified mixes covering 42 samples. Addition of GTR using wet process showed decrease in stiffness during loading. Cracking resistance of GTR modified mixtures increased with higher levels of dosages regardless of the base binder. An increase in the GTR dosage from 0 to 10% did not result in a significant change in fracture energy but a further increment to 25% increased the fracture energy. The laboratory Results indicated that 10% GTR was showed as the optimal content for the stiffness modulus and 25 % GTR as better content that provides better cracking resistance.

Rubber devulcanization in the planetary extruder – processing properties and structure

Thermo-mechanical devulcanization of ground tire rubber (GTR) in a planetary extruder was investigated. The processing parameters of recycled rubber were studied based on standardized protocols using a Mooney viscometer and a rubber processing analyzer (RPA). Fourier transform infrared spectroscopy and scanning electron microscopy were used to determine rubber structure. Devulcanization process upscaling limits processing properties of recycled rubber, which for partially devulcanized rubber can be determined only by RPA rheometer.

تحضير وتقييم بوليمرات رخيصة كمضادات للبكتريا ،الاكسدة ومثبطات تاكل لسبيكة من نوع N80 في تركيز 0.1N من حامض الفسفوريك

في هذا العمل ، تم تحضير بولي بوتادين (PBD) من نفايات الاطارات . وطعم البولي بوتادين المهلجن باستخدام أحادي وثنائي وثلاثي إيثانول امين ، ودرس التطعيم عن طريق حيود الأشعة السينية والمسح المجهري الإلكتروني. وتشير الخواص الحرارية (TGA, DSC) إلى أن المركبات المحضرة تمتلك ثابتًا حرارياً حتى 202 درجة مئوية. باستخدام تقنيات الاستقطاب الديناميكي الفعال ، تم قياس تأثيرات الامتزاز والتآكل للبوليمرات الثلاثة المطعمة على فولاذ N80 في.0.1N H3PO4 في اربع درجات حرارية مختلفة : 25 و 35 و 45 و 55 درجة مئوية. وقد اظهرت البوليمرات المحضرة كفاءة تثبيط ممتازة عند درجات الحرارة المختلفة. يعتبر pBut-g-mono ethanol amine هو الأكثر فعالية كمثبط للتآكل في جميع درجات الحرارة المختبرة. كما ان سلوك الامتزاز للبوليمرات الثلاث تخضع لمخطط لانجموير ، وقيم الطاقة الحرة المتحصلة توضح ان الامتزاز الذي يحدث على سطح N80هو من النوع المختلط كما تشير منحنيات تافل إلى أن البوليمرات المختبرة تعمل كمثبطات أنوديك وكاثودية مختلطة. من ناحية أخرى ،وجد أن جميع البوليمرات المحورة أظهرت خصائص متميزة كمضادة للأكسدة وللبكتيريا.

Laboratory performance and field demonstration of asphalt overlay with recycled rubber and tire fabric fiber

The escalating number of vehicles has precipitated a surge in tire production, resulting in an increased accumulation of waste materials such as ground tire rubber (GTR) and tire fabric fibers. Integrating recycled materials into asphalt pavement stands as a viable solution to mitigate the issue of waste accumulation. The objective of this study was to assess the durability and aging resistance of hot mix asphalt (HMA) enhanced with GTR and tire fabric fibers, in contrast to traditional HMA. A high-quality pavement incorporating GTR, and tire fibers was constructed in Michigan. Findings indicated that the inclusion of tire fabric fibers markedly bolstered the rutting and cracking resistance of HMA. Viscoelastic testing further confirmed the superior rutting and cracking resistance of the asphalts modified with GTR alone and in combination with tire fibers, relative to conventional asphalt. Additionally, field evaluations of noise levels showed a 2–3 dB decrease in noise with GTR-modified asphalt pavements, and after two years in service, the overlays modified with GTR and fibers exhibited no cracking. Ultimately, asphalt pavements modified with both rubber and tire fibers demonstrated enhanced performance over traditional pavements, offering a quieter and more durable roadway solution.