Analysis and Prospect of the Current Status of Waste Rubber Devulcanization Technology in the World

The results show that reactive extrusion is a promising way to desulfurize rubber. Waste tire management is a serious global environmental issue. Therefore, finding low-cost and industrial-scale tire recycling methods is gaining more and more attention.

 

Waste tire rubber is a valuable source of secondary raw materials for the circular economy, and current trends indicate that the use of waste rubber in the manufacture of value-added products will increase rapidly in the near future. Sustainable development of rubber devulcanization (replasticization) technology and appropriate cradle-to-cradle design of rubber products are the most promising strategies to achieve higher levels of rubber recycling.

The latest developments in waste tire rubber devulcanization technology in patents of various countries, including dynamic devulcanization, reactive extrusion, microwave treatment and other less popular methods. Special attention is paid to the used composition, rubber processing conditions and static mechanical properties of the recycled rubber. The results show that the recycled rubber described in the patents has higher tensile strength and elongation at break (depending on the devulcanization technology, median: 16.6-19.0 MPa and 321-443%) compared with literature data (median: 10.3 MPa and 309%) or commercial products (median: 6.8 MPa and 250%). The significant differences in the properties of recycled rubber observed are mainly due to the devulcanization efficiency related to the waste tire composition or source and rubber processing conditions. Considering environmental and economic aspects, reactive extrusion is the most promising method for further development of rubber devulcanization technology.

1. Introduction
The growing automotive industry generates increasing amounts of waste in the form of used tires, which account for as much as 80% of all rubber waste generated in the world. It is estimated that the number of scrap tires is about 1 billion per year. The management of such wastes, as well as the potential threats posed by conventional recycling strategies to the environment and human health, is poorly studied. On the other hand, proper management is a great challenge for scientists and industry representatives. Overall, for reasons of higher quality and safety, the strategies for the recycling of rubber that are economically favorable and environmentally friendly are being constantly revised and reconsidered in recent times.
Today, the most common methods for recycling used tires include: i) civil engineering in safety barriers using the whole tire, ii) energy recovery, especially incineration in cement kilns, iii) pyrolysis and iv) material recovery, including mechanical disintegration of used tires and further use of prepared tire rubber (GTR).
According to statistics published by the European Tire and Rubber Manufacturers Association (ETRMA) (ETRMA, 2021), in 2019 an average of 95% of used tires in Europe were recycled by the above methods. This means that a further 5% of tires are discarded, incinerated or illegally landfilled. Among the rubber recycling methods, material recycling is the most promising and involves the reuse of waste in the production of new materials. Scrap rubber as a valuable source of raw materials reduces the demand for virgin polymers, which are mainly petroleum products. The first attempt to recycle vulcanized rubber waste was through the grinding method adopted by Charles Goodyear, the inventor of vulcanization, more than 150 years ago. However, further investigations on a larger scale were carried out in the late 1900s. Figure 1 shows the progress in rubber recycling over the past 20 years (A) and the leading countries in the field of publication between 2000 and 2021 (B).

Figure 1 (A) Recent scientific papers and patents on rubber recycling; (B)

Country contribution to the development of rubber recycling (data according to Scopus on January 28, 2022)

As can be seen from Figure 1 (A), the number of papers published in this field has increased from 10 in 2000 to 147 in 2021 (almost 15 times), while just in the last three years (2018-2021) it has experienced a very sharp rise from 48 to 147 (almost 3 times). The increasing number of publications highlights the global importance of waste tire recycling technology and the significant economic investments in this field. In particular, the current level of waste tire recycling and reuse in many countries is still low. For example, in Poland, at least 75% of tires put on the market should be recycled, but only 15% need to be recycled. This trend fully justifies the organization of more research centers around the world aimed at commercializing rubber recycling methods.
Although patents are also recorded annually (on average 15 per year), their importance from a practical point of view is rarely emphasized. Considering legislation and environmental policies, it is no doubt that the number of patents emphasizing stable and environmentally friendly products rich in recycled rubber will also show a similar trend in the near future. According to the data shown in Figure 1 (B), the countries with the highest share of rubber recycling development are China, the United States, India and Poland. Although many review works related to rubber devulcanization have been published to date, most of them mainly focus on the "classical division" based on the energy used: thermal, mechanical, chemical or their combination. On the other hand, the literature data show the lack of a comprehensive review of patents covering innovative solutions that can be used for large-scale devulcanization. Based on recent patents and published papers, the latest developments in rubber devulcanization technology are reviewed, including the classification, analysis and discussion of the advantages and disadvantages of the most common patented rubber devulcanization methods. In addition, the potential limitations and future trends of rubber devulcanization technology are emphasized. This work is particularly helpful for scientists and industry representatives who are looking for promising directions in the field of rubber recycling, which can inspire them to develop new technologies as well as modify, functionalize or optimize existing solutions.
2. GTR Recycling and Devulcanization
Currently, tire rubber (GTR) is considered to be the main source of commercially available recycled rubber.
Economic aspects, easy availability of GTR and increasing environmental awareness have led to a current strong interest in the modification or suitable functionalization of GTR to make it a value-added product for advanced uses, such as blending with other thermoplastics or as an asphalt modifier.
"Rubber devulcanization" or "rubber recycling" plays a vital role in this process. According to ASTM D 6814, "devulcanization" is defined as the process of decomposition of chemical crosslinks in vulcanized rubber. On the other hand, ASTM D 1566 defines the term "recycled rubber" as vulcanized rubber that has been thermally, mechanically and/or chemically plasticized to be used as a rubber diluent, filler or processing aid.
It can be noted that these terms are slightly different from each other, however, currently both terms are used interchangeably in many articles and patents due to their similar functionalities. In fact, devulcanization and regeneration are modification and replasticization processes that aim to improve the interfacial interactions between GTR and other components in the blend, thereby improving the material's properties. Rubber devulcanization can be considered as the selective cleavage of crosslinks to destroy the three-dimensional structure, while rubber regeneration is a combination of backbone degradation and crosslink cleavage. Figure 2 shows the possible reactions during GTR thermal treatment to highlight the main differences between rubber devulcanization and regeneration. In addition, it can be observed that GTR thermal treatment may also favor undesirable secondary crosslinks caused by free radical recombination, which should be considered during experimental planning in this field.

Figure 2 Possible reactions during GTR heat treatment
In theory, crosslinks can be broken without degrading the backbone because the energy required to break C-C bonds is slightly higher than that of C-S and
S-S bonds, i.e., 348, 273, and < 227
kJ/mol. However, in practice, rubber products have more C-C bonds in the rubber backbone than
S-S crosslinks. Therefore, the probability of backbone degradation is much higher. In addition, most rubber products contain various rubbers (or mixtures thereof) and fillers (e.g., carbon black, silica), which also limits the selective breaking of crosslinks in the material.
The vulcanization of recycled rubber blended with virgin rubber may affect the performance of the product, which depends critically on the rubber particle size, purity (complete removal of steel, textiles, etc. from the tire), composition, devulcanization method, and process conditions. For example, the tensile strength of vulcanized recycled rubber is usually claimed in patents to be about 8 MPa, but in practice it rarely exceeds 5 MPa. Reducing the size of GTR particles, as well as adding virgin rubber or various additives are among the strategies that have been recently used to improve the mechanical properties of recycled rubber products. In many papers, devulcanizing agents such as organic disulfides and mercaptans are often used to recycle rubber. Based on these chemicals, many processes have been developed and subsequently patented. This approach can improve the processing and performance characteristics of recycled rubber. However, environmental factors should also be considered, as the rubber recycling process needs to be low-polluting and the additives used should be non-toxic. One of the most important factors affecting the efficiency of scrap tire recycling is the quality of GTR. The material composition varies depending on the intended use of the tire (truck, passenger car or off-road vehicle) and the climate zone, but the ingredients used for tire production remain relatively the same. The composition of GTR is estimated to be a mixture of natural rubber (NR), isoprene rubber (IR) and synthetic rubbers such as butadiene rubber (BR) and styrene butadiene rubber (SBR) 58– 60wt% – 28 wt% carbon black and silica, 3– 4 wt% vulcanizing agent and 8– 11 wt% other additives such as antioxidants, antiozonants or softeners. Literature shows that the composition of GTR can be divided into volatile compounds 7.0 ± 0.2 wt%, rubber (NR/IR, BR, SBR) 56.3 ± 2.1 wt% and carbon black + ash 36.7 ± 2.2wt% respectively. Recently, the literature showed how the composition of scrap tires affects the quality of recycled GTR. The tensile strength and elongation at break of recycled rubber are: i) 5-8 MPa for passenger car tires (GTRcar) and < 200%; ii) 8-12 MPa and 200-300% for truck tires (GTR), and iii) 14-15 MPa and 400% for truck treads. This trend is closely related to the composition of GTR (e.g. natural rubber/synthetic rubber in tread, carbon black content, ash content, etc.) and its purity (e.g. textile fibers). Natural rubber (NR) and synthetic rubber (SBR, BR) have different thermal stabilities and therefore different devulcanization kinetics. For example, GTR is prepared by the retreading process of truck tires, which results in a dry tread net uniform GTR composed mainly of NR and BR. On the other hand, the base rubbers used for GTR are NR and SBR, and SBR is difficult to recycle due to its easy secondary crosslinking at higher temperatures. In addition, the formulations and ingredients used by different tire manufacturers affect the quality of GTR, especially in the case of passenger car tires and truck tires as a whole.
Therefore, a suitable characterization of GTR, not limited to simple sieve analysis, is very important for the further sustainable development of scrap tire recycling technologies. Studies without this approach may lead to incorrect or overestimated findings and conclusions. In this field, thermogravimetric analysis based on ASTM
D6370 allows quantitative determination of: organic matter (oil, polymers), carbon black + ash and seems to be the best method for GTR composition evaluation. On the other hand, Mooney viscosity and tensile parameters (tensile strength, elongation at break) determined according to ISO/ASTM standards provide useful information about the processing and performance characteristics of recycled GTR. This approach allows easy comparison of standardized test results obtained by independent research groups, which are presented in the next subsections.
3. State of the art: patented methods for rubber devulcanization
In general, work on rubber devulcanization can be classified in terms of papers and patents.
In many review articles, rubber devulcanization methods are classified in a classical way, i.e., according to the methodology of the type of energy used for recovery. In general, thermal energy (conventional heat, microwave radiation), mechanical energy (shear force) and chemical energy (chemical substances) are most commonly used for rubber processing. Some other methods, such as ultrasound or biological, have also been considered for desulfurization. However, current technology largely utilizes a combination of these methods, such as thermochemical, thermomechanical and mechanochemical desulfurization. The rubber desulfurization methods developed in patents are not classified according to the energy used, but are almost limited to the description of the equipment and formulation used. Therefore, in the patent analysis, the desulfurization methods of rubber are divided into: i) dynamic desulfurization, ii) reactive extrusion, iii) microwave treatment and iv) others. 3.1 Dynamic desulfurization At present, most patents describing the production of recycled rubber use a thermochemical method, using a special tank for dynamic desulfurization. This method is commonly used in industry because the products obtained by this method have significantly higher mechanical properties compared to recycled rubber prepared by other methods. It is carried out at high temperature and pressure in the presence of water. Auxiliary agents such as activators and softeners are substances that must be added during the devulcanization process, and their selection directly affects the quality of the resulting material. Although the process is easy to handle, the additives used in this process may produce strong odors and pollution. In addition, the main limitations of dynamic devulcanization of waste rubber are related to water and energy consumption and heavy pollution emissions. With increasingly stringent environmental protection requirements, dynamic devulcanization should be gradually replaced by greener methods. In recent years, many attempts have been made to develop more ecological devulcanization processes by replacing toxic compounds with additives of natural origin. The most commonly used additive in rubber devulcanization is rosin. It is a natural resin that is the residue after the distillation of turpentine from the resin of coniferous trees (mainly pine trees) and can be used as a binder, softener or regenerator in the rubber devulcanization process. Other environmentally friendly substances often chosen by inventors are tall oil and pine tar. However, it should be noted that the resin acids present in these components are very corrosive at high temperatures (150– 300 °C), which requires the use of special equipment made of corrosion-resistant alloys.
Regarding the properties, the tensile strength and elongation at break of the reclaimed rubber vary in the following ranges:
10– 23.2 MPa (median: 16.6 MPa) and 335– 550% (median: 443%), depending on the formulation. Although this method has environmental issues, it is worth mentioning that the mechanical properties of the product are very high, keeping in mind the use of reclaimed rubber. This unexpected property may be caused by the GTR composition or source rather than the devulcanization method. It can be suspected that high-quality reclaimed rubber can be achieved by selecting certain parts of tires rich in natural rubber (such as tread) or using tire residues after production.
On the other hand, a detailed analysis of the relevant patents can conclude that a more common problem of dynamic devulcanization is the low stability of the Mooney viscosity of the reclaimed rubber prepared by this method. During storage, the Mooney viscosity value may increase by 3 to 4 times per day. It leads to significant processing difficulties and reduces the quality of the final product. Therefore, further development of research focusing on reclaimed rubber with stable Mooney viscosity should be considered.
3.2 Reactive extrusion

Compared to dynamic devulcanization, reactive extrusion is a more environmentally friendly method for rubber devulcanization. Thermomechanical and/or mechanochemical rubber devulcanization is performed using extruders with special plasticizing unit configurations, capable of generating considerable shear forces. For the recycling of waste rubber, co-rotating twin-screw extruders are most often used, which provide effective plasticization and homogenization with acceptable process efficiency.

The degree of devulcanization depends largely on barrel temperature and screw speed. It was found that using a suitable screw configuration can also improve product properties.

The great potential of this method stems from the fact that rubber devulcanization can be carried out effectively without the use of any additives under certain conditions.

Another advantage of the extruder is proper heat transfer, low oxidation of GTR and easy removal of off-gassing (volatile organic compounds released during rubber devulcanization).

In addition, unlike other methods, rubber extrusion devulcanization is a continuous, short-time and efficient process.

On the other hand, the main disadvantages of this technology are the high initial costs associated with the purchase of the extruder and supporting equipment, as well as the limited length of the plasticizing unit, which may lead to insufficient degree of devulcanization.

Due to the strong and elastic properties of GTR, durability and proper maintenance of the extruder is also a challenge. The presence of sulfur in the rubber may cause corrosion problems when operating at higher temperatures for a long time. It has been found that in many patents, a common strategy to obtain high-quality rubber products is the treatment of GTR with additives, such as a substance containing the chemical group SONH, a mixture of rosin and bitumen, a mixture of aromatic hydrocarbon disulfides and various tars or oils, polyalkylphenol disulfides, tall oil and pine tar. Another interesting way to enhance the reactive extrusion of GTR is to add thermoplastics. However, the final properties of the obtained material depend largely on the type and content of thermoplastic used as a modifier. The inventors pointed out that the tensile strength and elongation at break of the proposed material are in the range of: 7-31 MPa (median: 19 MPa) and 82-560% (median: 321%), respectively. However, it should be mentioned that in some cases 50%wt of thermoplastics were used, which indicates that some of the obtained materials are thermoplastic/GTR mixtures rather than standard recycled rubber.
Several inventors focused on improving the degree of devulcanization of waste rubber by multiple extrusions, claiming that recycled rubber with satisfactory mechanical properties (tensile strength above 9 MPa) can be obtained by a simple method without adding any additives. In addition, the proposed technology can be highly automated. It is expected that the production line can reach an annual production efficiency of 16,000 tons. Others have proposed an unconventional devulcanization method by extrusion in the presence of carbon dioxide or alcohol at critical pressure, respectively. This method improves the selectivity of breaking crosslinks; therefore, the efficiency of devulcanization is high.
In recent years, low-temperature extrusion has received increasing attention due to the reduction in energy consumption and the significant reduction in toxic gas emissions. This way of rubber recycling is more environmentally friendly and should be developed in the future.
3.3 Microwave treatment
In the patent, another method used to produce recycled rubber is microwave treatment. The characteristic of this method is that the energy delivered to the waste rubber (microwave irradiation) can be precisely controlled by selecting suitable processing parameters (e.g. magnetron power, treatment time). As a result, a high selectivity of sulfur bond cleavage over main chain degradation can be achieved. This method allows efficient desulfurization in a very short time (average of a few minutes). Microwave desulfurization is said to be at least 5 times more efficient than other methods. The process itself is environmentally friendly (solvent-free and energy-saving), but the emission of volatile degradation products into the atmosphere is a serious problem.

Patents related to microwave desulfurization Compared with the previously mentioned methods, patented methods for the production of reclaimed rubber using microwave irradiation are uncommon. Microwave irradiation and magnetron power are key parameters affecting the mechanical properties of reclaimed rubber. It can be concluded that a desulfurization process with a microwave irradiation power of 800 W for 100 s may lead to promising results (tensile strength above 23.7 MPa, elongation at break above 450%).

However, the efficiency of microwave treatment of waste rubber depends on the rubber composition, especially the carbon black content.
The role of carbon black in microwave devulcanization of NR vulcanizates has been studied in the literature. The waste rubber was modified in a microwave oven with an electric stirring system set at 40 rpm. The treatment time was 5 min and the magnetron power was 700 W. It was found that the temperature of the crosslinked rubber after microwave (MW) treatment and the sol fraction in the reclaimed rubber were proportional to the carbon black content. It can be noted that microwave treatment of NR with 60 phr of carbon black allowed reaching temperatures above 300°C and a sol fraction of 55%, while for the sample with 20 phr, the values ​​of these parameters were only 138°C and 22%. In addition, in some works, the vulcanization of rubber after microwave treatment for short times (up to 5 min) was described. This observation confirms the importance of the characteristics of the waste rubber before use, which could otherwise explain unexpected results related to microwave treatment of ground rubber, which should be verified and explained. 3.4 Other methods of rubber devulcanization
Although rubber devulcanization based on the above methods has been well implemented to some extent,
research in this field is still developing. Therefore, some other attempts to improve the efficiency of rubber devulcanization from the perspective of quality and quantity have been made, mainly by using different process machines. Patented technology featuring rubber devulcanization
It is worth mentioning that equipment already used in the rubber industry can be successfully adopted for rubber devulcanization. It was shown that reclaimed rubber of satisfactory quality can be produced using only an internal mixer. GTR was mixed with a softener, a coupling agent and a recycling agent and treated in an internal mixer at 170 ° C for 3.5 hours. The authors claimed that the tensile strength and elongation at break of the reclaimed rubber could even reach 19.5 MPa and 500%, respectively. A method for producing low Mooney viscosity reclaimed rubber using an internal mixer and a kneading machine without any additives was proposed. The inventors claimed that the reclaimed rubber obtained could be successfully used as an additive for asphalt in an amount ranging from 5-50% of the weight of asphalt to improve its quality and extend its service life.
In 2013, an idea for devulcanizing waste rubber using an alternating electric field was disclosed. Similar to microwave devulcanization, this method provides the appropriate energy to the rubber particles by selecting specific parameters. Another unconventional technology has been described, namely the devulcanization of rubber in the presence of 2-butanol and carbon dioxide. According to the inventors, the regenerated rubber obtained can be applied in quantities of up to 40 phr together with the virgin rubber in rubber products of the same type as the virgin rubber, such as tires, hoses or belts. The inventors also claim that there is no degradation in processing and mechanical properties. 4.Recycled Rubber Characterization: Patents, Literature, and Commercial Products
In general, patents cover innovative solutions that can be implemented on an industrial scale.
Therefore, in order to obtain a better and more critical overview, the results of the patent-based analysis in the field of rubber devulcanization were compared with the scientific papers reported so far and the technical information provided for commercially available recycled rubber.
The most prevalent rubber recycling method in scientific papers is extruder thermomechanical devulcanization, while both thermomechanical and thermochemical devulcanization dominate among industrial methods. The most common method described in the literature is reactive extrusion based on GTR, while it is difficult to find published research articles on dynamic devulcanization. For the recycled rubber described in the literature, the tensile strength and elongation at break ranged from 1.5-19 MPa (median: 10.3 MPa) and 78-540% (median: 309%), which are lower values ​​compared to those described in patents.
It should be noted that the recycled rubber companies we examined started to produce recycled rubber less than 15 years ago. This is related to the implementation of green desulfurization technologies and the openness of start-ups in this field, especially in China, France or Canada, which seems to be developing in other countries in the near future.
Regardless of the method used, the mechanical properties of the reclaimed rubber claimed by the producers are significantly lower than those proposed in the patents, but are basically consistent with those described in the literature. The tensile strength and elongation at break of commercially available reclaimed rubber range from 2.5– 11 MPa (median: 6.8 MPa) and 150– 350% (median: 250%).
In order to better understand the correlation between the desulfurization technology and the final properties of the obtained reclaimed rubber, Figure 3 shows a summary of the range of mechanical properties of reclaimed rubber described in patents, literature and commercial data.

Figure 3 Comparison of mechanical properties (A – tensile strength and B – elongation at break) of recycled GTR described in patents, literature and commercial data
.Conclusions, limitations and future trends
Waste tires, if not properly managed, pose a serious threat to the environment and human health. Therefore, the sustainable development of waste tire recycling technologies is gaining more and more attention. As a result, rubber recycling is becoming a value-added processing rather than a general strategy for the reuse of waste rubber materials used previously. Such methods can be classified into: i) use of whole tires in civil engineering, ii) energy recovery, iii) pyrolysis, or iv) material recovery. In the field of rubber material recycling, devulcanization is one of the most promising methods.
This work summarizes the literature, especially the recently patented rubber devulcanization methods in terms of the components used, processing conditions and mechanical properties of the recycled rubber obtained. Moreover, it was found that most of the patents used dynamic devulcanization methods (especially in China) or reactive extrusion methods, while microwave devulcanization was rarely used, which is related to the expensive equipment required for this method. In addition, it was found that the tensile properties of the recycled rubber described in the patents were generally higher than those in the literature or commercial data. In the studied patents, the mechanical properties (median values ​​of tensile strength and elongation at break) of the recycled rubber were: 16.6 MPa and 443% for dynamic devulcanization, 19.0 MPa and 321% for reactive extrusion, and 18.3 MPa and 414% for microwave devulcanization. On the other hand, for the recycled rubber described in the literature, the median values ​​of the tensile parameters were: 10.3 MPa and 309%, while for the commercial product: 6.8 MPa and 250%, respectively. The significant differences may be related to the distinct differences in GTR treatment conditions, depending on the devulcanization technology used, but a more important factor seems to be the GTR composition (car, truck, tread) or post-production or post-consumer origin. Current research trends indicate that green devulcanization of scrap tires and the production of GTR-based materials dedicated to high-value end markets will develop in the near future, in line with the strategy of the circular economy. Therefore, in further research in this field, proper classification and comprehensive characterization of scrap rubber before use are highly recommended. This approach significantly improves the process reproducibility and performance of the obtained rubber recycling products. From an environmental point of view, dynamic devulcanization is the most polluting method due to the presence of water, very high processing temperatures and the toxicity of the activators used. Reactive extrusion appears to be the most environmentally friendly method for rubber devulcanization, provided that it is carried out at moderately high temperatures and without the use of harmful additives. Moreover, reactive extrusion of GTR seems to be the most suitable for industrial-scale applications due to its efficiency and versatility. The properties of the recycled rubber prepared by reactive extrusion can be easily adjusted or modified by various parameters, such as processing temperature, screw speed, plasticizing unit configuration or suitable additives. In summary, future research in this area should focus on: i) optimization of devulcanization conditions (e.g., lowering temperature, reducing energy or water consumption, etc.) and eliminating or reducing toxic gas emission levels during rubber decomposition; ii) application of renewable and non-toxic additives; iii) combining devulcanization with appropriate functionalization or modification of GTR (approaches related to rubber upcycling strategies); iv) upgrading of devulcanization technology (implementing laboratory results to large-scale production).

 

Part II Rubber Semi-High Temperature Regeneration and Plasticization Technology Report 1. Process Roadmap:

2. Concept of Rubber Regeneration
Rubber regeneration and recycling has been a topic of concern and research for many years by professionals at home and abroad.
We proposed the concept of rubber regeneration because no one has restored or truly regenerated vulcanized rubber to the level of raw rubber. It is not like the recycling of metals such as steel, copper, and aluminum. Rubber regeneration refers to restoring the plasticity of vulcanized rubber through chemical and mechanical actions so that it can be used again.
.RV-RB Rubber Semi-High Temperature Regeneration and Regeneration Aid (Rubber Regeneration Aid)

RV-RB is a dark yellow powdered additive with an initial melting point of 70°C. It is tasteless and odorless. The usage is 3‰~5‰. It is a green additive and is the best choice for producing odorless and environmentally friendly recycled rubber.
4. RV-RB application example RV-RB
Use our company's high-shear and high-speed special rubber re-plasticizing kneading machine 20 liters and 140 liters
to conduct experiments and production.
Experimental formula: (20 liter kneading machine)
Actual ratio
20 mesh rubber powder 10021 kg
Rubber recycling additive RV-RB 0.50.105 kg
Softening oil 51.05 kg
Resin (rosin, solid Malone or C5 resin) 20.42 kg
Total 107.522.575 kg

Production formula: (140L kneading machine)
Actual quantity
Tire rubber powder 20 mesh 140 kg
Rubber regeneration agent RV-RB 0.7 kg
Softening oil 7 kg
Resin (rosin, solid malone or C5 resin) 2.8 kg
Total: 150.5 kg
Note: Softening oil is an aromatic oil produced in Iran 5. Process
First, put the rubber powder, RV-RB, softening oil and resin into a special kneading machine,
mix and knead for 10-15 minutes, and discharge when the temperature reaches 150℃.
Second, the discharged material enters the conveying screw to the cold mixer for cooling and parking.
Third, after cooling and parking, it directly enters the screw refiner (MRSRM) for refining once,
and then enters the ordinary refiner to discharge the flakes, completing the regeneration process.
Fourth, you can also add rubber vulcanization aids after the discharge from the screw refiner and mix in the internal mixer, and then directly vulcanize into solid tires or rubber sheets.
6. Product inspection
Vulcanization temperature 150℃, vulcanization time 10min.
Main technical indicators:
Tread rubber powder: production of rubber powder from different manufacturers (distinguished by A, B, C)

7. Result analysis
The above data show that the green rubber recycling (kneading + refining) method can produce rubber that meets and exceeds the GB/T 13460-2008 national standard for recycled rubber and the T/CRIA21001-2018 E series recycled rubber standard.
8. Applicable materials
Waste tire rubber powder, waste rubber scraps rubber powder, natural latex gloves, condoms, balloons, nitrile gloves, neoprene, etc.