Special Issue "Recent Advances in Rubber Recycling"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: 30 September 2020.

Special Issue Editor

Dr. Krzysztof Formela
Website
Guest Editor
Department of Polymer Technology, Faculty of Chemistry, G. Narutowicza Str. 11/12, Gdańsk University of Technology, 80-233 Gdańsk, Poland
Interests: plastics and rubber recycling; reactive processing; composites; polymer blends and composites compatibilization; bitumen modification
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Special Issue Information

Dear Colleague, 

Dynamic development of the automotive industry and growing demand for rubber products has resulted in an increasing amount of waste rubber, especially in end-of-life tires. Illegally discarded and landfilled waste tires are a serious threat to the environment and human health. Therefore, their further utilization is currently one of the biggest challenges of 21st-century waste management.

At present, the vast majority of waste tires are used as alternative fuel in cement kilns and power plants, which allows energy recovery. The common application of this method is mostly related to economic factors, because alternative industrial recycling technologies are rather limited. On the other hand, laboratory scale research is still pursuing new methods in order to provide competitive environmentally friendly utilization or up-cycling of waste tires.

The Special Issue “Recent Advances in Rubber Recycling” presents a collection of original research and reviews focused on engineering and technical solutions to support the development of the sustainable utilization of waste rubber.

Selected example topics include:

  • Waste tires grinding technologies
  • Design and processing of polymer composites, concretes and bitumens modified with ground tire rubber
  • Strategies for compatibilization and improvement of the interactions between matrix and ground tire rubber
  • Green reclaiming/devulcanization methods
  • Pyrolysis and gasification as a sustainable method of energy recovery from waste tires
  • Current trends in upcycling of rubber recycling products

Dr. Krzysztof Formela
Guest Editor

Manuscript Submission Information

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Keywords

  • Waste tires
  • Recycling
  • Grinding
  • Environmentally friendly composites
  • Compatibilization
  • Modification
  • Functionalization
  • Bitumen
  • Reclaiming/Devulcanization
  • Pyrolysis

Published Papers (10 papers)

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Research

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Open AccessArticle
Initial Field Validation of Poroelastic Pavement Made with Crumb Rubber, Mineral Aggregate and Highly Polymer-Modified Bitumen
Materials 2020, 13(6), 1339; https://doi.org/10.3390/ma13061339 - 15 Mar 2020
Abstract
Tire/road noise in most driving conditions dominates other sources of traffic noise. One of the most efficient ways of reducing tire/road noise is to use the so-called “low noise pavement”. According to numerous studies, at present, poroelastic road pavement that is composed of [...] Read more.
Tire/road noise in most driving conditions dominates other sources of traffic noise. One of the most efficient ways of reducing tire/road noise is to use the so-called “low noise pavement”. According to numerous studies, at present, poroelastic road pavement that is composed of rubber and mineral aggregate and polyurethane or bituminous binder gives the best noise reduction up to 12 dB. Unfortunately, there are many problems with making durable poroelastic pavements. This article presents the first results of a project that is executed in Poland and aims at the development of a durable, low noise poroelastic pavement based on polymer-modified asphalt binder called Safe, Eco-friendly POroelastic Road Surface (SEPOR). Two test sections were built in 2019 to test the production technology and performance of the SEPOR pavement. It is observed that some of the problems with previous poroelastic materials were mainly eliminated (especially delamination from the base layer and raveling) but noise reduction is a little less than expected (up to 9 dB). Rolling resistance for car tires is acceptable and fire properties (damping of spill fuel fires, toxic gas emission) are very good. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessArticle
Assessment of the Environmental Impact of a Car Tire throughout Its Lifecycle Using the LCA Method
Materials 2019, 12(24), 4177; https://doi.org/10.3390/ma12244177 - 12 Dec 2019
Cited by 1
Abstract
There are numerous threats to the natural environment that pose a significant risk both to the environment and to human health, including car tires. Thus, there is a need to determine the impact of the life cycle of car tires on the environment, [...] Read more.
There are numerous threats to the natural environment that pose a significant risk both to the environment and to human health, including car tires. Thus, there is a need to determine the impact of the life cycle of car tires on the environment, starting with the processes of raw materials acquisition, production, and ending with end-of-life management. Therefore, the authors of this study chose to do research on passenger car tires (size: P205/55/R16). As part of the research, the life cycle assessment (LCA) of traditional car tires was performed with the use of the Eco-indicator 99, cumulative energy demand (CED), and Intergovernmental Panel on Climate Change (IPCC) methods. The level of negative effects was determined for the life cycle of a tire and its particular stages: Production, use, and end of life. The negative impact on the atmosphere, soil, and water, as well as on human health, the environment, and natural resources was also investigated. The results show that the most energy-absorbing stage of a car tire life cycle is the use stage. It was found that the most harmful impact involves the depletion of natural resources and emissions into the atmosphere. Recycling car tires reduces their negative environmental impact during all their life cycle stages. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessFeature PaperCommunication
Preliminary Investigation on Auto-Thermal Extrusion of Ground Tire Rubber
Materials 2019, 12(13), 2090; https://doi.org/10.3390/ma12132090 - 28 Jun 2019
Cited by 1
Abstract
Ground tire rubber (GTR) was processed using an auto-thermal extrusion as a prerequisite to green reclaiming of waste rubbers. The reclaimed GTR underwent a series of tests: thermogravimetric analysis combined with Fourier-transform infrared spectroscopy (TGA-FTIR), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), [...] Read more.
Ground tire rubber (GTR) was processed using an auto-thermal extrusion as a prerequisite to green reclaiming of waste rubbers. The reclaimed GTR underwent a series of tests: thermogravimetric analysis combined with Fourier-transform infrared spectroscopy (TGA-FTIR), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and static headspace and gas chromatography-mass spectrometry (SHS-GC-MS) in order to evaluate the impact of barrel heating conditions (with/without external barrel heating) on the reclaiming process of GTR. Moreover, samples were cured to assess the impact of reclaiming heating conditions on curing characteristics and physico-mechanical properties. Detailed analysis of the results indicated that the application of auto-thermal extrusion is a promising approach for the sustainable development of reclaiming technologies. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessArticle
Microscopic Properties of Hydrogen Peroxide Activated Crumb Rubber and Its Influence on the Rheological Properties of Crumb Rubber Modified Asphalt
Materials 2019, 12(9), 1434; https://doi.org/10.3390/ma12091434 - 02 May 2019
Cited by 2
Abstract
Crumb rubber modified (CRM) asphalt binder has been affirmed to improve resistance to rutting, moisture susceptibility, low-temperature cracking, and asphalt durability. However, CRM has poor compatibility with asphalt since crumb rubber molecules are vulcanized. The objective of this study was to develop a [...] Read more.
Crumb rubber modified (CRM) asphalt binder has been affirmed to improve resistance to rutting, moisture susceptibility, low-temperature cracking, and asphalt durability. However, CRM has poor compatibility with asphalt since crumb rubber molecules are vulcanized. The objective of this study was to develop a new method to prepare activated crumb rubber using hydrogen peroxide (H2O2) solution and to explore the rheological properties of H2O2 activated CRM (ACRM) asphalt. Three different percentages of H2O2 solution were used to activate crumb rubber. The surface properties of oxidized rubber were analysed using scanning electron microscopy. Moreover, the pore structure in rubber powder was investigated. The rheological properties of bitumen samples obtained from treated and untreated rubber were characterized by conducting dynamic shear rheometer tests. The test results show that the average pore size of the crumb rubber after activation with H2O2 solution is significantly smaller than that of the inactivated crumb rubber, and the volume and surface area of the crumb rubber pores change with H2O2 solution activation in a certain pattern. With the increase in H2O2 solution content, the contact surface between the particles increases, the floccules and pores of the powder increase, and the interface degree between the crumb rubber powder and the asphalt is strengthened. Solubility of the rubber hydrocarbon and the release ability of the carbon black particles from the crumb rubber in the asphalt binder increase, but the mechanical properties of the crumb rubber, including the strength, elasticity, and wear resistance, decrease. As a result, a reduction is observed in the elasticity, viscosity, high-temperature rutting resistance, and elasticity of the ACRM asphalt. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessArticle
Modification of Pyrolytic Oil from Waste Tyres as a Promising Method for Light Fuel Production
Materials 2019, 12(6), 880; https://doi.org/10.3390/ma12060880 - 15 Mar 2019
Cited by 4
Abstract
Due to its high total sulphur content and other unfavourable properties, pyrolytic oil obtained as a result of tyres pyrolysis is not suitable for use as motor or heating fuel. Therefore, pyrolytic oil was hydrorefined. Hydrorefined oil was used as a component of [...] Read more.
Due to its high total sulphur content and other unfavourable properties, pyrolytic oil obtained as a result of tyres pyrolysis is not suitable for use as motor or heating fuel. Therefore, pyrolytic oil was hydrorefined. Hydrorefined oil was used as a component of light heating oil. A composition was prepared from 30 wt % hydrorefinate with 70 wt % Ekoterm Plus (a commercial oil). Unfortunately, the flash point temperature of the hydrorefinate was too low, and did not allow fuel compliant with the Polish standard PN-C-96024:2011 for L1 light heating oil to be obtained. Therefore, the fraction with boiling point below 180 °C was removed from the hydrorefinate. The residue, with a flash point of 74 °C and a sulphur content of 0.143 wt %, was mixed with Ekoterm Plus and fuels with a hydrorefinate fraction content of 30 and 50 wt % were prepared. The composition containing 30 wt % met the requirements for L1 oil in the whole range of tested parameters. Total sulphur content was 0.092 wt %, specific weight was 856 kg/m3 and closed cup flash point was 64 °C. However, the composition containing 50 wt % hydrorefinate did not meet the requirements regarding sulphur content and specific weight. Sulphur content, specific gravity, and flash point are the parameters limiting the possibility of using hydrorefined pyrolytic oil for composing light heating oils compliant with the mentioned standard. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessArticle
Implications of the Use of Silica as Active Filler in Passenger Car Tire Compounds on Their Recycling Options
Materials 2019, 12(5), 725; https://doi.org/10.3390/ma12050725 - 01 Mar 2019
Cited by 3
Abstract
Tires are an important vehicle component, as car handling, safety and fuel economy depend for a major part on the tire composition and construction. As a consequence, tires are improved continuously. The most prominent improvement in the recent past was the use of [...] Read more.
Tires are an important vehicle component, as car handling, safety and fuel economy depend for a major part on the tire composition and construction. As a consequence, tires are improved continuously. The most prominent improvement in the recent past was the use of a silica-silane filler system in passenger car tread compounds, instead of traditionally used carbon black. For recycling and re-use of end-of-life car tire rubber one of the most promising recycling methods is devulcanization: re-plasticizing the vulcanized rubber by selectively breaking the sulfur bridges between the polymer molecules. In the present paper, the influence of silica, which is present in the passenger car tires granulate, on both devulcanization and subsequent revulcanization, is investigated. In a step-wise approach it is shown that the presence of silica influences both devulcanization and revulcanization. The best tensile strength of the revulcanizate, using a carbon-black-based revulcanization formulation, was 5 MPa. This could be improved to 6.5 MPa by using 2.8 phr of 1,3-DiPhenylGuanidine (DPG) in the revulcanization formulation. After addition of a silanization step during revulcanization by adding 3.2 phr bis[3-(TriEthoxySilyl)Propyl] Tetrasulfide (TESPT), a silane, to the formulation, the tensile strength of the revulcanizate was further improved to 8 MPa. With these results it is shown that the silica in the granulate can be used to improve the revulcanization properties. To check the benefits of using pure tire tread material for the devulcanization and subsequent revulcanization, of both a carbon black and a silica-based virgin tread compound, it is shown that a tensile strength of the revulcanizate of 13 MPa can be reached. This shows the potential of devulcanized rubber when the various tire components are separated before whole car tire material is granulated as the beginning of the recycling. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessArticle
Application of Crumb Rubber in Cement-Matrix Composite
Materials 2019, 12(3), 529; https://doi.org/10.3390/ma12030529 - 10 Feb 2019
Cited by 4
Abstract
Many studies have used rubber as an additive to form a cement-matrix composite (rubcrete). However, rubcrete has a lower mechanical strength than standard concrete. To improve the properties of rubcrete, this study performed surface modifications on crumb rubber through a partial oxidization reaction. [...] Read more.
Many studies have used rubber as an additive to form a cement-matrix composite (rubcrete). However, rubcrete has a lower mechanical strength than standard concrete. To improve the properties of rubcrete, this study performed surface modifications on crumb rubber through a partial oxidization reaction. The optimal ratio of air to nitrogen was determined by experiments to be 1:4. Fourier transform infrared spectroscopy (FT-IR) was used to identify the functional groups on the surface of the crumb rubber. A colloidal probe of calcium silicate hydrate (C–S–H) was prepared, and the intermolecular interactions between the rubber and the C–S–H were measured using an atomic force microscope (AFM). The experimental results showed that the partially oxidized crumb rubber contained more hydrophilic S–O bonds. The intermolecular force between C–S–H and treated rubber increased by 23% compared to the force between the original rubber and C–S–H. The compressive strength of the hardened cement paste (56 days) with the treated crumb rubber increased 50% in comparison with that of the hardened cement paste with the as-received crumb rubber. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Review

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Open AccessReview
Waste Tyres Pyrolysis for Obtaining Limonene
Materials 2020, 13(6), 1359; https://doi.org/10.3390/ma13061359 - 17 Mar 2020
Abstract
This review deals with the technologies of limonene production from waste tyre pyrolysis. Thermal decomposition is attractive for tackling the waste tyre disposal problem, as it enables both: energy to be recovered and limonene to be obtained. This material management recycling of tyres [...] Read more.
This review deals with the technologies of limonene production from waste tyre pyrolysis. Thermal decomposition is attractive for tackling the waste tyre disposal problem, as it enables both: energy to be recovered and limonene to be obtained. This material management recycling of tyres is environmentally more beneficial than the burning of all valuable products, including limonene. Given this recoverability of materials from waste tyres, a comprehensive evaluation was carried out to show the main effect of process conditions (heating rate, temperature, pressure, carrier gas flow rate, and type of volatile residence and process times) for different pyrolytic methods and types of apparatus on the yield of limonene. All the results cited are given in the context of the pyrolysis method and the type of reactor, as well as the experimental conditions in order to avoid contradictions between different researchers. It is shown that secondary and side reactions are very sensitive to interaction with the above-mentioned variables. The yields of all pyrolytic products are also given, as background for limonene, the main product reported in this study. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessReview
Devulcanization Technologies for Recycling of Tire-Derived Rubber: A Review
Materials 2020, 13(5), 1246; https://doi.org/10.3390/ma13051246 - 10 Mar 2020
Abstract
In general, composite materials are difficult to recycle. Tires belong to this class of materials. On top, one of their main constitutents, vulcanized rubber, is as elastomer, which cannot be remolten and hence is particularly challenging to put to a new use. Today, [...] Read more.
In general, composite materials are difficult to recycle. Tires belong to this class of materials. On top, one of their main constitutents, vulcanized rubber, is as elastomer, which cannot be remolten and hence is particularly challenging to put to a new use. Today, the main end-of-life routes of tires and other rubber products are landfilling, incineration in e.g., cement plants, and grinding to a fine powder, generating huge quantities and indicating a lack of sustainable recycling of this valuable material. True feedstock recycling is not feasible for complex mixtures such as tires, but devulcanization can be done to reactivate the cross-linked polymer for material recycling in novel rubber products. Devulcanization, i.e., the breaking up of sulfur bonds by chemical, thermophysical, or biological means, is a promising route that has been investigated for more than 50 years. This review article presents an update on the state-of-the art in rubber devulcanization. The article addresses established devulcanization technologies and novel processes described in the scientific and patent literatures. On the one hand, tires have become high-tech products, where the simultaneous improvement of wet traction, rolling resistance, and abrasion resistance (the so-called “magic triangle”) is hard to achieve. On the other hand, recycling and sustainable end-of-life uses are becoming more and more important. It is expected that the public discussion of environmental impacts of thermoplastics will soon spill over to thermosets and elastomers. Therefore, the industry needs to develop and market solutions proactively. Every year, approximately 40 million tons of tires are discarded. Through the devulcanization of end-of-life tires (ELT), it is possible to produce new raw materials with good mechanical properties and a superior environmental footprint over virgin products. The devulcanization process has become an interesting technology that is able to support the circular economy concept. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessReview
Waste Rubber Recycling: A Review on the Evolution and Properties of Thermoplastic Elastomers
Materials 2020, 13(3), 782; https://doi.org/10.3390/ma13030782 - 08 Feb 2020
Cited by 1
Abstract
Currently, plastics and rubbers are broadly being used to produce a wide range of products for several applications like automotive, building and construction, material handling, packaging, toys, etc. However, their waste (materials after their end of life) do not degrade and remain for [...] Read more.
Currently, plastics and rubbers are broadly being used to produce a wide range of products for several applications like automotive, building and construction, material handling, packaging, toys, etc. However, their waste (materials after their end of life) do not degrade and remain for a long period of time in the environment. The increase of polymeric waste materials’ generation (plastics and rubbers) in the world led to the need to develop suitable methods to reuse these waste materials and decrease their negative effects by simple disposal into the environment. Combustion and landfilling as traditional methods of polymer waste elimination have several disadvantages such as the formation of dust, fumes, and toxic gases in the air, as well as pollution of underground water resources. From the point of energy consumption and environmental issues, polymer recycling is the most efficient way to manage these waste materials. In the case of rubber recycling, the waste rubber can go through size reduction, and the resulting powders can be melt blended with thermoplastic resins to produce thermoplastic elastomer (TPE) compounds. TPE are multi-functional polymeric materials combining the processability of thermoplastics and the elasticity of rubbers. However, these materials show poor mechanical performance as a result of the incompatibility and immiscibility of most polymer blends. Therefore, the main problem associated with TPE production from recycled materials via melt blending is the low affinity and interaction between the thermoplastic matrix and the crosslinked rubber. This leads to phase separation and weak adhesion between both phases. In this review, the latest developments related to recycled rubbers in TPE are presented, as well as the different compatibilisation methods used to improve the adhesion between waste rubbers and thermoplastic resins. Finally, a conclusion on the current situation is provided with openings for future works. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Planned Paper 1

Authors: Prof. Jerzy Ejsmont (pg.edu.pl) and Dr. Piotr Jaskula (pg.edu.pl).

Planned Paper 2

Author:  Prof. Javier Cañavate (@upc.edu)

Planned Paper 3

Author: Dr. Krzysztof Formela

Planned Paper 4

Title: Recent Advances in Rubber Recycling

Author: Prof. Denis Rodrigue and Dr. Ali Fazli

Outline:

1.    Introduction    
1.1.    Waste rubber types    
1.2.    Microstructural composition    
1.2.1.    Elastomers    
1.2.2.    Fillers    
1.2.3.    Other additives    
1.3.    Rubber Characteristics    
1.3.1.    Mechanical properties of rubber
1.3.2.    Thermal properties of rubber    
2.    Rubber Recycling/Reclamation Process    
2.1.    Vulcanization    
2.2.    Reclamation of vulcanized rubber    
2.3.    Reclaiming agents, oils, catalysts and reaction mechanism    
2.4.    Methods of Recycling/Reclamation    
2.4.1.    Physical Methods    
2.4.2.    Chemical Methods    
2.4.3.    Biological Method    
3.    Advantages and Application of Using Reclaimed Rubber    
3.1.    Advantages of using reclaimed rubber    
3.2.    Applications of recycled/reclaimed rubbers    
4.    Rubber/Polymer Blends    
4.1.    Thermoplastic elastomers (TPE)    
4.2.    Thermoplastic vulcanizates (TPV)    
4.3.    Processing methods of TPE and TPV    
4.4.    Compatibilaztion    
4.4.1.    Physical compatibilization    
4.4.2.    Chemical compatibilization    
5.    Recent development of TPE and TPV    
6.    Environmental Hazards    
7.    Future directions    
8.    Conclusion

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