Ground Tire Rubber Research Articles

Ground tire rubber functionalization as a promising approach for the production of sustainable adsorbents of environmental pollutants.

Waste tires management and further utilization are currently one of the biggest concerns regarding the environment and human health protection. At present, shredding, grinding, or pulverization of waste tires are the most popular options for industrial recycling. Although many solutions for ground tire rubber (GTR) applications were checked and verified so far, their further implementation at an industrial scale is still very limited. In this brief review work, ground tire rubber functionalization strategies as a promising approach for the production of sustainable adsorbents of environmental pollutants were presented and discussed. Our findings indicate that suitable functionalization of GTR significantly improves adsorption capacity or selectivity of prepared GTR-based adsorbents. However, it should be mentioned that most of the performed research based on multi-step and time-consuming protocols of GTR functionalization is performed usually in the presence of solvents, which results in very low efficiency and as a consequence high-cost and limited applications. Current research trends showed that reactive extrusion can be considered as efficient, solvent-free, and pro-ecological alternative for commonly investigated periodic methods of GTR functionalization. This work shows that reactive extrusion is a promising method for further development of GTR-based adsorbents dedicated to environmental pollutants.

Effect of Ethylene-1-Butene as a Compatibilizer for the Optimization of Wood Flour and Ground Tyre Rubber in Polypropylene Composites

The use of waste materials to make eco-friendly wood-polymer composites has been explored by many researchers for academic and industrial purposes due to the low cost, biodegradability, and availability of waste wood flour. Polypropylene (PP)/ground tyre rubber (GTR)/wood flour (WF) composites were prepared using an internal batch mixer at a temperature of 165 °C for 8 min, and the samples were injection-moulded at 190 °C with a pressure of 6 MPa. The design of the experimental approach was used to determine and optimize the proportions of each component in the composites. The morphology of the untreated composites showed more voids and the agglomeration of fillers, namely WF and GTR, in the PP matrix. Fewer voids, as well as improved distribution, were observed in the compatibilized composites. The incorporation of ethylene-1-butene as a compatibilizer improved the thermal stability and elongation at the break of the composites. The addition of WF increased the elongation at break and decreased the tensile strength of the composites. Overall, the use of statistically designed experiments has aided in attaining the optimum formulations of the wood flour–polymer composites.

Application of Balanced Mix Design Strategies to Missouri Dense-Graded Asphalt Mixtures

This study focused on the improvement or redesign of dense-graded mixtures in Missouri by applying various strategies typified by a balanced mix design (BMD) approach. Briefly, the BMD approach involves designing mixtures using appropriate thresholds of mixture performance tests to control major distresses. In this study, two existing dense-graded mixtures from Missouri were adopted with 33% binder replacement by recycled asphalt pavement (RAP). Appropriate thresholds from three commonly used cracking tests, namely the disk-shaped compact tension test, or DC(T), the Illinois Flexibility Index Test (I-FIT), and the indirect tensile asphalt cracking test (IDEAL-CT), were paired with the Hamburg wheel track test (HWTT) toward the improvement or rebalancing of mixes designed before the availability or specified use of these tests. Preliminary test results showed that the existing mix designs did not satisfy the cracking thresholds adopted in this study, and thus the following modifications were made to the mixtures: (a) replacing the base binder with a softer grade binder, (b) adding a rejuvenator, and (c) adding ground tire rubber (either 10% or 20% by weight of base binder). According to the results, modification with rubber and softer binder was the most efficient strategy for improving and balancing DC(T) fracture energy and HWTT performance. On the other hand, the use of a softer binder or rejuvenator led to the best success in meeting semicircular bend (SCB) (I-FIT) and IDEAL-CT test requirements in balance with HWTT requirements.

A sustainable strategy for reprocessable elastomer based on ground tire rubber

The value-added applications of ground tire rubber (GTR) have attracted more attention in the field of environmental conservation. In this paper, a sustainable strategy was exploited for the fabrication of reprocessable elastomer (GTRE) based on 100% GTR. A synthetically difunctional nitroxides compound, namely DTEMPO, with desulfurization and crosslinking effects on GTR was employed. GTR was mechano-chemically modified via DTEMPO at room temperature. The dynamic crosslinked network was subsequently introduced into GTRE by alkoxyamine reaction between GTR and DTEMPO. The mechanical strength of GTRE could be tailored to range from 7.6 MPa to 12.2 MPa by varying content of DTEMPO. Electron spin resonance analysis indicated that the dynamic reversibility of obtained alkoxyamine bonds were controlled by temperature. With the dissociation and reformation of alkoxyamine crosslinking structure, GTRE was capable of reprocessing multiple times and recovering most of the original mechanical strength (greater than 83%). This strategy is expected to offer a sustainable and environmentally friendly method for the recycling of GTR.

Synergistic effects of gamma pre-irradiation and additional vulcanizing agent in case of ground tire rubber containing vulcanizates

In this study, we investigated gamma radiation treated ground tire rubber (GTR) at different doses and measured the soluble content and the cross-link density of the samples. These results have been evaluated with Horikx's diagram. The results showed that at low doses, the selective chain-scission of the sulphur cross-links is dominant; however, at higher doses, the degradation of the polymer backbone comes to the fore. Natural rubber (NR) based mixtures were prepared in an internal mixer using conventional and two-step mixing, then the samples were vulcanized. Synergistic effects were observed when using radiation treatment and two-step mixing, resulting in improved mechanical properties. In materials where only one treatment was applied, the properties did not change significantly. The morphology of the mixtures was observed using scanning electron micrographs, which showed that the GTR could integrate well into the matrix.

A practical manner to GTR recycling in waste-HDPE/ABS

Waste high-density polyethylene (w-HDPE)/ acrylonitrile–butadiene–styrene (ABS)/ground tire rubber (GTR) have been melt blended by two-roll milling. Ternary blends of w-HDPE/ABS/GTR have been observed to be incompatible in the composition range studied which revealed in the deteriorated mechanical properties. Two main types of compatibilizers such as an experimental olefin-maleic anhydride copolymer based one synthesized by the authors and a commercial maleic anhydride grafted polypropylene (MA-g-PP) have been chosen for enhancing compatibility between the components ergo the mechanical properties. For characterizing tensile and impact properties of the blends mechanical tests have been carried out besides the scanning electron microscopy (SEM), X-ray diffraction and Fourier transform infrared spectroscopy. The most advantageous result in industrial practice can be that the experimental additive allows to apply higher GTR concentration ergo gives the opportunity to recycle higher level of GTR.

Recycle of waste tire rubber in a 3D printed composite with enhanced damping properties

Management of waste tires has become a leading environmental issue due to the global growth in the number of tires produced annually. This work is focused on exploring the use of Ground Tire Rubber (GTR) in a new class of cost-effective, recycled composite materials. A Fused Filament Fabrication (FFF) desktop 3D printer is used to produce GTR-based composite material with up to 50% wt. rubber filling. ABS is used as the host matrix. Both microscopic and macroscopic characterization of the 3D printed composites are performed in addition to a baseline printed composite. Increasing the rubber content from 0 % wt. to 50 % wt. in the 3D printed GTR-based composite results in approximately 260% improvement in the overall damping properties. Results also indicate the average diameter of the rubber particles in the 3D printed composites increased as the amount of rubber content increased. Presumably, specimens with larger rubber particles yielded longer contact lines with the host polymeric matrix. Consequently, energy dissipation is improved, resulting in enhanced overall damping properties of the 3D printed composites. The enhanced damping capabilities as well as the low-production cost and lightweight characteristics of the presented GTR-filled composite yield new opportunity for application of these GTR-reinforced composites in automotive or other industries for making a wide variety of parts where these characteristics are highly valuable.

Solving the Dichotomy between Self‐Healing and Mechanical Properties in Rubber Composites by Combining Reinforcing and Sustainable Fillers

AbstractThe dichotomy between mechanical performance and repairability is a well‐known fact in the self‐healing field. One alternative to overcome this trade‐off is the inclusion of reinforcing fillers. In this research, hybrid reinforced self‐healing styrene‐butadiene rubber (SBR) composites are developed by combining mechano‐chemically modified ground tire rubber (mGTR) with carbon black (CB). The SBR matrix is systematically analyzed by means of dynamic mechanical analysis and broadband dielectric spectroscopy. The SBR composite reinforced with 20 phr mGTR and 20 phr CB maintains the healing efficiency of the unfilled SBR (80%) and improves its tensile strength by 300%, balancing perfectly well both properties. The healing efficiency is determined at different damage levels. The damage at the microscopic scale is easier to recover and does not depend on the presence of fillers, while the recovery at the macroscopic level clearly relies on the addition of filler, with more demanding healing conditions.

Thermoplastic elastomers based on recycled high-density polyethylene/ground tire rubber/ethylene vinyl acetate: Effect of ground tire rubber regeneration on morphological and mechanical properties.

This work investigates the properties of different types of regenerated recycled rubbers (RR1 and RR2) to produce thermoplastic elastomers (TPE) based on recycled high-density polyethylene (RHD) as the matrix. The higher regeneration degree of RR2 (24%) compared to RR1 (15%) was able to better restore the plasticity and processability of the ground tire rubber (GTR). So better entanglement between RR2 free chains and the thermoplastic macromolecules was obtained inducing stronger interfacial interaction leading to higher elongation at break (159%) and impact strength (342J/m) of the blends filled with 80 wt.% RR2. To further improve the adhesion and achieve rubber-like properties, ethylene vinyl acetate (EVA) was used as a compatibilizer. The microstructure analysis showed that uniform dispersion of the particles and ground tire rubber encapsulation by EVA increased the resistance to crack propagation and failure of the compatibilized blends. The swelling, mechanical and physical properties of the ternary blends (RHD/GTR/EVA) showed that EVA improved the interfacial interactions between GTR and RHD which was confirmed by enhanced elongation at break (203%) and impact strength (379J/m) by the addition of 10 wt.% EVA.

Simultaneous effect of CaCO3 nanoparticles and waste ground rubber tire powder on forced vibration of polypropylene nanocomposite plates: An experimental investigation

In this study, the effect of the simultaneous incorporation of different contents of CaCO3 nanoparticles (NPs) and waste ground rubber tire powder (WGRT) on the forced vibration behavior of polypropylene (PP) was experimentally investigated. Hammer test with modal analysis was performed to investigate the vibrational behavior of the composite plates with one edge clamped (CFFF) support condition. Microstructural assessment of composites using Field Emission Scanning Electron Microscope (FESEM) images showed that a rise in CaCO3 nanoparticles in small weight percentages led to better dispersion and a decline in the tire phase size in the small weight percentage of WGRT. Moreover, a comparison of the modal analysis results revealed that all ternary composites, except in the first mode, had a higher damped natural frequency than pure PP. The damping ratio of all ternary composites, especially in the first and second modes, was higher than pure PP, which is due to the combined effect of WGRT and CaCO3 nanoparticles in increasing energy dissipation and damping of composites.

Morphological, mechanical, and physical properties of ground rubber tire thermoplastic elastomer/rubberwood sawdust composites: Effects of composition contents and rubber types

Waste tire disposal is a growing challenge among major cities worldwide because each year, a huge number of end-of-life tires is generated. The current study aimed to evaluate the potential of ground rubber tire (GRT) and waste rubberwood sawdust (RWS) as materials for developing wood-polymer composites (WPCs). The effects of the compositions’ contents and rubber types on the mechanical and physical properties, as well as the morphology of the thermoplastic elastomer (TPE)/RWS composites were investigated. The results revealed that the addition of about 30–60 wt% of RWS improved the modulus of elasticity, compressive modulus, and hardness of the TPE composites based on both the GRT and natural rubber (NR). With the same RWS content and rubber type, the TPE/RWS composites with rubber/plastic blends of a 30/70 ratio clearly yielded better mechanical and physical properties than those blends with a 40/60 ratio. The addition of about 2–4 wt% of maleic anhydride-grafted polypropylene (MAPP) improved all the properties of the TPE/RWS composites. Overall, the composites based on the GRT gave superior strength, rigidity, and dimensional stability than that based on NR. It is therefore suggested that the eco-friendly TPE composites made from GRT and waste rubberwood could be a suitable replacement for the inorganic filler-natural rubber composites for saving costs and the environment.

The effect of ground tire rubber modified by deep eutectic solvents on the viscoelasticity of silica‐filled styrene‐butadiene rubber

AbstractWith the development of the recycling economy for waste rubber, the high‐value application of rubber powder, such as the modifier in asphalt mixture and the polyurethane foam, has attracted more and more attention. In the study, the surface characteristics of rubber powder modified by deep eutectic solvents were investigated by infrared spectroscopy, sol fraction, solid surface energy, and scanning electron microscope. The mechanical properties of modified ground tire rubber powder (M‐GTR)/SBR/silica composites were studied. Meanwhile, the viscoelasticity of the composites was characterized by the Payne effect and Mullins effect. Compared with the unmodified rubber powder, the rubber powder treated at 105°C had a higher sol fraction and maximum value of solid surface energy. With the increase of the content of M‐GTR, the Payne effect of the M‐GTR/SBR/silica composites firstly weakened and then increased. As for the Mullins effect, the vulcanizates showed stress‐softening phenomenon in the process of uniaxial cyclic compression. The recovery ability of the Mullins effect strongly depended on temperature. Besides, the modified rubber powder could improve the dispersity of silica in the SBR matrix, and the Mullins effect of the composite contained modified rubber powder was weak, which would provide potential high‐value application for rubber powder.

Microcellular ground tire rubber/ethylene vinyl acetate compounds: Mechanical properties and structure relationships

AbstractThis study aims to investigate the effect of ground tire rubber (GTR) treated by acetone on mechanical and morphological properties of ethylene‐vinyl acetate (EVA) matrix. Polymeric EVA/GTR (0, 10, 20, 30, and 40 phr) compounds were achieved through extrusion and batch foaming process. TGA and NMR analysis revealed that oils and additives were removed from the GTR after the acetone treatment. Morphological characterization showed cell sizes below 100 μm in the compounds with treated GTR, which improved the mechanical performance of EVA/GTR compounds. The results indicated that the acetone‐treated GTR are a suitable raw material to obtain foam compounds useful in vibrations absorber and isolation applications.

Towards Circular Economy by the Valorization of Different Waste Subproducts through Their Incorporation in Composite Materials: Ground Tire Rubber and Chicken Feathers.

Incorporation of residua into polymeric composites can be a successful approach to creating materials suitable for specific applications promoting a circular economy approach. Elastomeric (Ground Tire Rubber or GTR) and biogenic (chicken feathers or CFs) wastes were used to prepare polymeric composites in order to evaluate the tensile, acoustic and structural differences between both reinforcements. High-density polyethylene (HDPE), polypropylene (PP) and ethylene vinyl acetate (EVA) polymeric matrices were used. EVA matrix defines better compatibility with both reinforcement materials (GTR and CFs) than polyolefin matrices (HDPE and PP) as it has been corroborated by Fourier transform infrared spectroscopy (FTIR), termogravimetric analysis (TGA) and scanning electron microscopy (SEM). In addition, composites reinforced with GTR showed better acoustic properties than composites reinforced with CFs, due to the morphology of the reinforcing particles.

Study of porous rubber pipes reinforced with waste tire fiber and pineapple leaf fiber for smart irrigation system

Global trend in waste management involves sustainable development for waste utilization according to the concept of circular economy. Wastes from worn-out tires have been known as a world problem and not yet to be resolved successfully. In this work, wastes from worn-out tires, i.e., ground tire rubber (GTR), reclaimed rubber (RR) and waste tire fiber (WTF) were used to produce reinforced porous rubber pipes as irrigation system for smart farming. Comparative study of porous rubber pipes reinforced with natural fibers (pineapple leaf fiber, PALF) was also carried out. The experiment was divided into 2 parts, i.e., porous sheets (model study) and extruded porous pipes. Compound samples were prepared by mixing GTR, RR, and natural rubber (NR) at a ratio of 60:20:20 (by weight) with other additives by using an internal mixer, then shaped into samples by using a compression molding machine (sheets) and a single-screw extruder (pipes). Samples were vulcanized by a hot air oven. Factors affecting sample properties were studied, such as, fiber types (WTF and PALF) and fiber loadings (0-15 phr). Properties of the samples were characterized, such as, mechanical properties, morphology, water permeability rate, and %diameter swell. It was found that tensile strength was increased up to an optimum point. Modulus (at 10% strain, M10) and hardness were increased with increasing fiber loading. However, %elongation at break had a trend to decrease. Morphologies of the composites made from both fibers were insignificantly different in fiber distribution. By adding the fibers, %diameter swell was clearly improved. Pipe samples were also tested in precision smart agriculture system. It can be proven that WTF and PALF can be used to reinforce the porous pipes and used as a watering device for precision irrigation system.

Demonstration Project for Ground Tire Rubber and Post-Consumer Recycled Plastic-Modified Asphalt Mixtures

Research has demonstrated that asphalt pavements can be a strategic destination for some of the major streams of waste materials around the globe, such as scrap tires and plastics. Ground tire rubber (GTR) from scrap tires has been used in asphalt pavements since the 1960s but has yet to approach its full potential in relation to market adoption. The heightened restrictions imposed by China in relation to waste stream contamination in 2018 have catalyzed research on incorporating post-consumer recycled (PCR) plastics into asphalt pavements. A field demonstration project was carried out in Columbia, MO to evaluate modern recycled plastic and GTR additives in an asphalt pavement overlay. The demonstration focused on dry-process modification, which requires minimal alterations to an existing asphalt plant and allows a higher amount of recyclates to be utilized. The project was also designed to assist in the Missouri Department of Transportation’s early roll-out of balanced mix design asphalt design and quality assurance specifications. The results of the study indicated the viability of dry-process GTR and PCR plastic additives used with neat (unmodified) asphalt binder as an alternative to binders modified with virgin polymers, chemical treatments, or both, in a wet process. The results of the study also suggest the viability of hybrid wet polymer-modified binder with dry-process PCR plastic as a greener alternative to binders modified with virgin polymers, chemical treatments, or both. Future studies will be needed to examine additional PCR plastic streams, especially mixed polymer streams.

Potential Valorization of Waste Tires as Activated Carbon-Based Adsorbent for Organic Contaminants Removal.

The present study investigates the potential of waste tires to produce a valuable adsorbent material for application in wastewater treatment. In the first stage, the pyrolysis of ground rubber tire was explored using non-isothermal and isothermal thermogravimetric analysis experiments. The effect of operating parameters, such as heating rate and pyrolysis temperature, on the pyrolysis product yields was considered. The slow pyrolysis of ground rubber tire was taken up in a large-scale fixed-bed reactor for enhanced char recovery. Four pyrolysis temperatures were selected by thermogravimetric data. The product yields were strongly influenced by the pyrolysis temperature; at higher temperatures, the formation of more gases and liquid was favored, while at lower pyrolysis temperatures, more char (solid fraction) was formed. The produced chars were characterized in terms of mineral composition, textural properties, proximate analysis, and structural properties to identify the relationships between the pyrolysis temperature and the char properties. In a second step, a series of activated chars were prepared, starting from the pyrolytic chars via chemical and/or physical activation methods. Then, the activated chars were characterized and tested as adsorbents for atrazine and ibuprofen. Adsorption experiments in aqueous media were carried out in a small-scale batch reactor system. Chemical activation seems appropriate to significantly reduce the inorganic compounds initially present in ground rubber tire and contribute to an important increase in the surface area and porosity of the chars. Adsorption experiments indicated that chemically activated chars exhibit high aqueous adsorption capacity for atrazine.

Ground Tire Rubber Modified by Elastomers via Low-Temperature Extrusion Process: Physico-Mechanical Properties and Volatile Organic Emission Assessment.

In this paper, low-temperature extrusion of ground tire rubber was performed as a pro-ecological waste tires recycling method. During this process, ground tire rubber was modified with constant content of dicumyl peroxide and a variable amount of elastomer (in the range: 2.5–15 phr). During the studies, three types of elastomers were used: styrene-butadiene rubber, styrene-ethylene/butylene-styrene grafted with maleic anhydride and ethylene-octene copolymer. Energy consumption measurements, curing characteristics, physico-mechanical properties and volatile organic compounds emitted from modified reclaimed GTR were determined. The VOCs emission profile was investigated using a passive sampling technique, miniature emission chambers system and static headspace analysis and subsequently quantitative or qualitative analysis by gas chromatography. The VOCs analysis showed that in the studied conditions the most emitted volatile compounds are dicumyl peroxide decomposition by-products, such as: α-methylstyrene, acetophenone, α-cumyl alcohol, methyl cumyl ether, while the detection level of benzothiazole (devulcanization “marker”) was very low. Moreover, it was found that the mechanical properties of the obtained materials significantly improved with a higher content of styrene-butadiene rubber and styrene-ethylene/butylene-styrene grafted with maleic anhydride while the opposite trend was observed for ethylene-octene copolymer content.

SELF-HEALING STRATEGIES IN RUBBER COMPOSITES

Inspired by some of the mechanisms that occur in nature, self-healing materials are characterized by the ability to recover, partially or totally, their initial properties after suffering damage. These materials constitute an efficient alternative for extending the lifecycle of products, as well as for reducing the amount of waste generated. At the same time, they reduce maintenance and repair costs. In this work, examples of recent developments in the field of elastomeric composite materials are presented, studying different matrices, natural rubber (NR), epoxidized natural rubber (ENR), styrene-butadiene rubber (SBR) and nitrile rubber (NBR), and using diverse repair strategies, hydrogen bonds, disulfide exchange reactions, Diels-Alder chemistry and ionic interactions. The effect of adding carbon-derived reinforcing fillers (graphene oxide) and sustainable alternative fillers (ground tire rubber) is also analyzed. It is studied how the presence and type of filler influences the healing capacity of elastomeric matrices, reaching repair efficiencies of up to ~80%, without detriment to their mechanical performance.

Performance Analysis and Environmental Sustainability of Asphalt Mixtures Containing Ground Tire Rubber (Gtr) and Nano Silica for Road Pavement Construction

Performance Analysis and Environmental Sustainability of Asphalt Mixtures Containing Ground Tire Rubber (Gtr) and Nano Silica for Road Pavement Construction