Description:
FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. TITLE OF THE INVENTION
Method and System for Devulcanization of Crosslinked Rubber

2. APPLICANTS

NAME : ALP Nishikawa Company Private Limited
NATIONALITY : IN
ADDRESS : Plot No. 32 (HUDA), Sector-18, Gurugram-122015, Haryana, India

2. PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD

[0001] The present invention relates to the field of rubber waste reprocessing and recycling, and more specifically to a chemical-free thermal mechanical devulcanization process, including the use of a twin-screw extruder, for devulcanization of the crosslinked rubber.

BACKGROUND
[0002] With growing environmental concerns, managing rubber waste has become a critical environmental and industrial challenge. This is particularly true for vulcanized or crosslinked rubbers, which are used in a variety of products across industries such as automotive, construction, infrastructure, and consumer goods.
[0003] The crosslinked rubbers are utilized due to their properties such as excellent weather resistance, flexibility, and mechanical durability, which are achieved through sulphur-based vulcanization or crosslinking. However, these crosslinked structures make the rubber highly resistant to degradation, rendering its recycling and reprocessing more difficult than that of thermoplastics or non-crosslinked elastomers.
[0004] Therefore, a recycling process is required that can break the sulphur-based crosslinking bonds without damaging the main polymer chains and restore the original physical and chemical state of the rubber, allowing its reuse in the manufacturing cycle after vulcanization treatment.
[0005] At present, there exist a number of recycling methods, among these existing methods devulcanization based recycling methods, whether thermal, chemical, mechanical, microwave, or ultrasonic, is considered one of the most sustainable approaches. These methods aim to cleave sulphur cross-links and recover processable rubber material for reintroduction into the manufacturing cycle. However, these methods are not environment-friendly and lack cost-effective scalability.
[0006] Furthermore, conventional devulcanization methods often suffer from major drawbacks such as chemical residues in the recovered rubber material, poor property retention, and limited industrial scalability.
[0007] In light of the foregoing discussion, there exists a need to address this problem by providing a chemical-free method and system for devulcanization of crosslinked rubber.

SUMMARY

[0008] The present invention provides a method for devulcanization of crosslinked rubber, wherein the devulcanization is chemical free, and the crosslinked rubber is vulcanized ethylene propylene diene monomer (EPDM). The method is performed in steps that include preprocessing the crosslinked rubber. In an embodiment, the preprocessing includes shredding the crosslinked rubber, grinding the crosslinked rubber to form rubber crumbs, and separating metal particles from the rubber crumbs using magnetic separation to provide metal-free rubber granules.
[0009] The steps further include feeding the rubber granules into a conveying hopper connected to a feed zone of a twin-screw extruder. The steps further include processing the rubber granules in the twin-screw extruder under a multi-stage temperature profile configured to break sulphur-based crosslinking bonds within the rubber and outputting the devulcanized rubber in strip form. The devulcanized rubber exhibits physical properties comparable to regular rubber compounds with respect to hardness, tensile strength, elongation, and specific gravity.
[0010] In an embodiment, the processing of dense and sponge rubber crumbs is performed separately if the rubber crumbs include both types to avoid any contamination or any negative influence on crosslinking of the recovered rubber.
[0011] In an embodiment, the multi-stage temperature profile includes at least 13 distinct temperature profiles each with a temperature range from 70°C to 360°.
[0012] In an embodiment, the devulcanized rubber is used as a component in rubber compound formulations in proportions ranging from 4% to 7% for extrusion applications and up to 10% for compression-moulded products.
[0013] In an another embodiment, the present invention discloses a system for devulcanization of crosslinked rubber. The system includes a preprocessing unit, which is configured to receive and preprocess the crosslinked rubber to provide metal-free rubber granules. In an embodiment, the preprocessing unit includes a size reduction unit, which is configured to produce rubber crumbs from the crosslinked rubber, and a separation unit, which is configured to separate metal particles from the rubber crumbs using a high-power magnet to provide metal-free rubber granules. In an exemplary embodiment, the size reduction unit includes a cracker for shredding the crosslinked rubber and a grinder for grinding the shredded rubber to produce rubber crumbs.
[0014] The system further includes a conveying hopper. The conveying hopper is configured to transfer the metal-free rubber granules to a feed zone of a twin-screw extruder.
[0015] Thereafter, the system includes the twin-screw extruder, which is configured to process the rubber granules received from the feed zone through distinct temperature profiles to break sulphur-based crosslinking bonds within the rubber and output devulcanized rubber strip. The crosslinked rubber is vulcanized ethylene propylene diene monomer (EPDM) rubber, and the temperature ranges from 70°C to 360 °C in each profile.
[0016] A primary objective of the present invention is to provide a chemical-free, efficient, and industrially scalable method for the devulcanization of crosslinked rubber, particularly sulphur-crosslinked EPDM.
[0017] A further objective of the present invention is to provide the devulcanized rubber in strip form, making it readily suitable for re-use in extrusion and compression molding applications.
[0018] Yet another objective of the present invention is to provide a devulcanization process that uses a twin-screw extruder, configured with multiple temperature profiles.
[0019] Yet another objective of the present invention is to provide a preprocessing unit for shredding and grinding the crosslinked rubber, and separating metal particle to generate clean, fine-mesh rubber granules suitable for devulcanization.
[0020] Yet another objective of the present invention is to provide a devulcanization process that converts the crosslinked rubber into original rubber compound without affecting key deliverables of the crosslinked rubber.
[0021] The foregoing summary is provided for illustrative purposes only and is not intended to limit the scope of the invention in any way. In addition to the illustrative aspects, embodiments, and features described earlier, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated herein and constitute a part of this disclosure, illustrate exemplary embodiments, and together with the description, serve to explain the disclosed principles. The same numbers are used throughout the figures to reference like features and components, wherein:
[0023] FIG. 1 depicts a flow diagram showing a method for devulcanization of crosslinked rubber, in accordance with one or more exemplary embodiments of the present disclosure;
[0024] FIG. 2A depicts a block diagram of a system for performing devulcanization of the crosslinked rubber, in accordance with one or more exemplary embodiments of the present disclosure;
[0025] FIG. 2B depicts a schematic diagram of a twin-screw extruder, in accordance with one or more exemplary embodiments of the present disclosure;
[0026] FIG. 3 depicts a Mooney Viscosity table, in accordance with one or more exemplary embodiments of the present disclosure; and
[0027] FIG. 4 depicts an example of transformation of vulcanized EPDM scrap into devulcanized rubber strips, in accordance with one or more exemplary embodiments of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0028] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that these specific details are only exemplary and not intended to be limiting.
[0029] It is to be understood that various omissions and substitutions of equivalents may be made as circumstances may suggest or render expedient to cover various applications or implementations without departing from the scope of the present disclosure.
[0030] Further, it is to be understood that the phraseology and terminology employed herein are for the purpose of clarity of the description and should not be regarded as limiting.
[0031] Furthermore, in the present description, references to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. The appearance of the phrase “in one embodiment” in various places in the specification does not necessarily refer to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
[0032] Further, the terms “a” and “an” used herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described, which may be requirements for some embodiments but not for other embodiments.
[0033] Referring to FIG. 1, a flow diagram showing a method for devulcanization of crosslinked rubber is disclosed. The method is used to convert the crosslinked rubber such as vulcanized ethylene propylene diene monomer (EPDM) into a form that can be reused or reprocessed into new rubber-based products. The disclosed method enables the recovery of rubber material from post-industrial or post-consumer waste, thereby supporting circular material use and improving sustainability in rubber manufacturing.
[0034] Crosslinking is a well-established chemical modification process used to transform soft, tacky raw rubber into a durable, elastic, and thermally stable material. This is achieved by creating crosslinks between long-chain rubber polymer molecules using sulphur or sulphur-containing agents, which is commonly referred to as vulcanization. The resulting sulphur crosslinks enhance the mechanical strength, resilience, and heat resistance of the rubber, making it suitable for various industrial applications such as tires, weatherstrips, seals, and hoses. It should be noted that the terms “vulcanization” and "crosslinking" may be used interchangeably throughout this disclosure, unless specified otherwise.
[0035] However, the formation of these sulphur crosslinks also renders the rubber a thermoset, which cannot be melted or reshaped like thermoplastics. As a result, conventional reprocessing and recycling methods are ineffective for crosslinked rubber.
[0036] Therefore, the devulcanization method described in the present invention is designed to reverse the vulcanization process by breaking the sulphur crosslinks (bonds) that connect the rubber molecules without damaging the main rubber structure. By maintaining the main structure, the devulcanized rubber retains mechanical and processing characteristics.
[0037] The method for devulcanization of crosslinked rubber may be explained in conjunction with a system disclosed in FIG.2A and FIG. 2B.
[0038] In the flow diagram, each block may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order noted in the drawings. For example, two blocks shown in succession in FIG. 1 may be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Any process descriptions or blocks in flowcharts should be understood as representing modules, segments, or portions of code that include one or more executable instructions for implementing specific logical functions or steps in the process, and alternate implementations are included within the scope of the example embodiments in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved. In addition, the process descriptions or blocks in flow charts should be understood as representing decisions made by a hardware structure, such as a state machine. The flow diagram starts at step (102) and proceeds to step (106).
[0039] At step 102, the crosslinked rubber is preprocessed. In one embodiment, the preprocessing includes shredding, grinding, and metal separation. It is important to note that the shredding is performed to reduce the size of the crosslinked rubber. In an exemplary embodiment, the crosslinked rubber may be post-industrial or post-consumer rubber waste, such as manufacturing scraps. This size reduction makes it easier to handle and process the crosslinked rubber in subsequent steps.
[0040] After shredding, the shredded rubber is subjected to grinding, which further reduces its size to form rubber crumbs. In an exemplary embodiment, the rubber crumbs are small, granulated pieces of rubber with a more uniform size distribution. This granulation improves the consistency and effectiveness of later devulcanization processes.
[0041] Post-grinding, metal particles are separated from the rubber crumbs using magnetic separation to provide metal-free rubber granules. These metal particles are often present in used rubber products. Magnetic separation ensures that the final output is composed of clean, metal-free rubber granules.
[0042] In an exemplary embodiment, the preprocessing stage provides uniformly sized, contaminant-free rubber particles, which serve as the input material for the devulcanization stage. This ensures high process efficiency, equipment protection, and improved quality and consistency of the recovered rubber compound.
[0043] Successively, the preprocessed rubber granules are fed into a conveying hopper, at step 104. The conveying hopper functions as an intermediate storage that is connected to a feed zone of a twin-screw extruder to ensure a consistent and controlled flow of rubber granules into the twin-screw extruder. The conveying hopper is typically designed in a funnel-shaped, allowing gravity-assisted or mechanically regulated feeding.
[0044] The feed zone of the twin-screw extruder is responsible for receiving and initially transporting the rubber granules into screw channels, where they will undergo subsequent thermal and mechanical treatment.
[0045] The use of the conveying hopper between the preprocessing unit and the twin-screw extruder ensures smooth transition of the rubber granules, continuous operation, and precise control over the input rate, which is essential for achieving uniform devulcanization.
[0046] Thereafter, the rubber granules are processed, at step 106 in the twin-screw extruder under a multi-stage temperature profile configured to break Sulphur-based crosslinking bonds within the rubber, and output the devulcanized rubber in strip form. In an embodiment, the strips are then strained through a mesh size ranging from 80 to 140, depending on the viscosity, to obtain uniform strips suitable for reuse.
[0047] Referring to FIG. 2, a block diagram of a system (200) for performing the devulcanization of crosslinked rubber is illustrated, in accordance with one or more exemplary embodiments of the present disclosure. As depicted, the system (200) includes a preprocessing unit (202). The preprocessing unit (202) is configured to receive and preprocess the crosslinked rubber to provide metal-free rubber granules. In an exemplary embodiment, the crosslinked rubber is vulcanized EPDM scraps, which are accumulated and stored in clean and dust-free areas to ensure material integrity before preprocessing.
[0048] The preprocessing unit (202) includes a size reduction unit (204) and a separation unit (206). In an embodiment, the size reduction unit (204) includes a cracker (204a), which is configured to shred the crosslinked rubber into smaller pieces, and a grinder (204b), which grinds the shredded rubber into finer particles, referred to as rubber crumbs.
[0049] The separation unit (206) is configured to separate metal particles from the rubber crumbs using a high-power magnet and provide metal-free rubber granules. This step is crucial to eliminate contaminants such as steel wires or metallic debris that may have been embedded in the crosslinked rubber during its original use or manufacturing.
[0050] In an additional embodiment, the preprocessing unit (202) further includes a classifier (not shown in the FIGs), which is used to identify and distinguish between different types of rubber crumbs, such as dense and sponge rubber crumbs. Based on the type, the system (200) performs devulcanization separately for each type of material, as dense and sponge rubbers may require different processing parameters. Furthermore, the preprocessing unit (202) may be equipped with storage hoppers or bins (Not shown in the FIGs) for temporary collection and holding of the metal-free rubber granules before they are utilized for further processing.
[0051] The system (200) further includes a conveying hopper (208), which is configured to convey the metal-free rubber granules to a feed zone (210a).
[0052] The system (200) further includes a twin-screw extruder (210) configured to process the rubber granules received from the feed zone (210a) through distinct temperature profiles to break sulphur-based crosslinking bonds within the rubber and output devulcanized rubber in strip form. The twin-screw extruder (210) may be explained in detail using FIG. 3.
[0053] Referring to FIG. 3, the twin-screw extruder (210) includes the feed zone (210a) configured to receive the rubber granules from the conveying hopper (208). The twin-screw extruder (210) further includes a pulverizing zone (210b), which is configured to mechanically shear and compress the granules between rotating screws. The twin-screw extruder (210) further includes a devulcanizing zone (210c), which is configured to provide distinct temperature profiles to break sulphur-based crosslinking bonds within the rubber. In an exemplary embodiment, the devulcanizing zone (210c) configured to provide at least 13 distinct temperature profiles. The twin-screw extruder (210) further includes a cooling zone (210d), which is configured to stabilize the devulcanized rubber and output the devulcanized rubber in strip form.
[0054] Table 1 discloses the distinct temperature profiles for various zones in the twin screw extruder:

Table 1: Temperature profile for various zones in the twin screw extruder

[0055] As depicted in table 1, Loop no discloses individual heating/cooling zones in the of twin screw extruder (Zones 1 to 20, including feed and water (cooling) zones are associated with temperature profiles represented by SP (°C) and PV (°C)).
wherein, SP (°C) discloses set point temperature, which is the target temperature configured for each zone,
PV (°C) discloses process value, which is the actual measured temperature in each zone during operation.
[0056] As disclosed in the table, Zones 1 to 13 have temperature setpoints from 70°C to 360°C. These high temperatures are critical for breaking sulphur crosslinks without damaging the polymer backbone. Actual process values (PV) closely follow the setpoints, indicating effective heat control.
[0057] Zones 14–16 have setpoints between 100°C and 120°C. These are likely part of a transition section where the rubber is stabilized or moisture is removed post-devulcanization.
[0058] The last loops labelled “F”, “Water”, etc. show low SP and PV values confirming the presence of a cooling zone.
[0059] Referring to FIG. 4, a Mooney Viscosity Table is disclosed, in accordance with one or more exemplary embodiments of the present disclosure.
[0060] Mooney viscosity (MU) measures the processability and flow characteristics of the devulcanized rubber. An optimal Mooney viscosity value indicates that the devulcanized rubber can be efficiently reused in extrusion and molding applications, without compromising its essential mechanical and physical properties.
[0061] As depicted, batch 11 has the highest Mooney viscosity values i.e., MUini (Initial Mooney Viscosity) is 72.73 MU and MU4 (Mooney at 4 minutes) is 41.61 MU, which indicates the devulcanized rubber has retained good polymer structure and processing consistency.
Stable viscosity slope (S4 = -1.15) suggests predictable flow behavior, which is important for production.
MUmin (Minimum Mooney) = 41.59 MU is significantly higher than other trials, indicating better resistance to thermal-mechanical breakdown.
tmin = 3.99 min shows stable curing behavior.
[0062] Referring to FIG. 5, an example of transformation of vulcanized EPDM scrap into devulcanized rubber strips is disclosed, in accordance with one or more exemplary embodiments of the present disclosure.
[0063] Referring to FIG.5, the left image depicts a vulcanized EPDM scrap which is post-industrial or post-consumer rubber product, such as automotive weatherstrips. Middle image depicts metal-free rubber granules, which are achieved by performing preprocessing as disclosed in FIG. 1 and FIG. 2A. These metal-free rubber granules serve as input for the devulcanization process.
[0064] After processing through a twin-screw extruder under a multi-stage thermal-mechanical profile, the metal-free rubber granules are converted into devulcanized rubber. The output is typically in sheet or strip form, as suitable for storage, handling, and further use in extrusion or compression molding applications. This rubber can be reused in new product formulations, reducing waste and material cost.
[0065] In an exemplary embodiment, the devulcanized crosslinked rubber can be used as a component in rubber compound formulations in proportions ranging from 4% to 7% for extrusion applications and up to 10% for compression-moulded products.
[0066] Table 2 discloses comparative analysis of the physical properties of regular rubber and devulcanized rubber, specifically at 5% recycle content.

S. No. Property Regular Trial 1 Trial 2
1 Hardness (Shore A) 68 71 71
2 Specific Gravity 1.30 1.32 1.31
3 Tensile Strength (kgf/cm²) 81.1 76.57 77.08
4 Elongation at Break (%) 174.56 153.46 170.34
5 M-100 53.77 56.83 52.9
Table 2: Comparative analysis of the physical properties of regular rubber and devulcanized rubber, specifically at 5% recycle content.

[0067] As shown in Table 2, the physical properties of the trial samples are very close to the regular compound, even with 5% devulcanized rubber content.
[0068] Key performance metrics such as tensile strength, elongation, and hardness are within industrially acceptable tolerances.
[0069] This confirms that the present chemical-free devulcanization method produces rubber of reliable quality suitable for reintegration into new rubber products—especially for applications like weatherstrips, seals, or molded components.
[0070] Table 3 discloses experimental data evaluating devulcanized rubber compound performance using different trials of recovered rubber obtained through the twin-screw extruder-based devulcanization process.
Table 3: Experimental data evaluating devulcanized rubber compound performance using different trials of recovered rubber.

[0071] As shown, the Table 3 is divided into two major trials (Trial 1 and Trial 2), each involving multiple sub-trials where devulcanized rubber (processed via the twin-screw extruder) is added into a dense rubber compound. Each row corresponds to a unique batch tested for rubber compound preparation and performance evaluation.
[0072] Each entry specifies that devulcanized rubber reclaimed from twin-screw extruder is added to a dense compound, which is the real-world application target of the invention i.e., incorporating recovered material into usable formulations.
[0073] In these trials, polymer K-8550 (7.300 KG) + M-3110, processing oil (16.0) are used.
[0074] P/L oil source (PANAMA) and carbon source (HINDAH) are used uniformly to avoid external influence.
[0075] • Carbon remains consistent, indicating any changes in results are due to the devulcanized rubber quality.
[0076] CMB numbers (batch IDs) are recorded for traceability and process tracking.
[0077] Dump temperatures are recorded around 173–180°C, typical for compound processing.
[0078] Mooney values (41–47.54 range) are stable across trials, reflecting that the devulcanized rubber has good processability and polymer chain integrity, supporting the invention's objective.
[0079] ML (minimum torque), MH (maximum torque), TS2 (scorch time), T90 (optimum cure time) values confirm that the devulcanized rubber blends well with virgin rubber.
[0080] Across trials, values like MH and ML remain within a controlled range. This shows the reclaimed rubber does not compromise compound performance, aligning directly with the goal of sustainable reuse without chemical aids.
[0081] It has thus been seen that the method and system for devulcanization of crosslinked rubber, according to the present invention, achieves the purposes highlighted earlier. Such a method and system can in any case undergo numerous modifications and variants, all of which are covered by the same innovative concept, moreover, all of the details may be replaced by elements that are technically equivalent. The scope of protection of the invention is therefore defined by the attached claims.

Dated 9th day of July, 2025
Ankush Mahajan
Agent for the Applicant (IN/PA-1523)
OF Global Institute of Intellectual Property Pvt. Ltd. , Claims:Claims
We Claim:
1. A method (100) for devulcanization of crosslinked rubber, the method (100) comprising:
preprocessing (102) the crosslinked rubber, wherein the preprocessing (102) includes shredding the crosslinked rubber, grinding the shredded rubber to form rubber crumbs, and separating metal particles from the rubber crumbs using magnetic separation to provide metal-free rubber granules;
feeding (104) the rubber granules into a conveying hopper connected to a feed zone of a twin-screw extruder; and
processing (106) the rubber granules in the twin-screw extruder under a multi-stage temperature profile configured to break sulphur-based crosslinking bonds within the rubber and outputting the devulcanized rubber strip.

2. The method (100) as claimed in claim 1, wherein the processing of dense and sponge rubber crumbs is performed separately if the rubber crumbs include both types

3. The method (100) as claimed in claim 1, wherein the devulcanization is chemical free, and the crosslinked rubber is vulcanized ethylene propylene diene monomer (EPDM).

4. The method (100) as claimed in claim 1, wherein the multi-stage temperature profile comprises at least 13 distinct temperature profiles and the temperature ranges from 70°C to 360 °C in each profile.

5. The method (100) as claimed in claim 1, wherein the devulcanized rubber exhibits physical properties comparable to regular rubber compounds with respect to hardness, tensile strength, elongation, and specific gravity.

6. A system (200) for performing devulcanization of crosslinked rubber, comprising:
a preprocessing unit (202) configured to receive and preprocess the crosslinked rubber to provide metal-free rubber granules, wherein the preprocessing unit (202) comprises
a size reduction unit (204) configured to produce rubber crumbs from the crosslinked rubber;
a separation unit (206) configured to separate metal particles from the rubber crumbs using a high-power magnet and provide metal-free rubber granules;
a conveying hopper (208) configured to transfer the metal-free rubber granules to a feed zone (210a); and
a twin-screw extruder (210) configured to process the rubber granules received from the feed zone (210a) through distinct temperature profiles to break sulphur-based crosslinking bonds within the rubber and output devulcanized rubber strip.

7. The system (200) as claimed in claim 6, wherein the size reduction unit (204) comprises a cracker (204a) for shredding the crosslinked rubber and a grinder (204b) for grinding the shredded rubber to produce rubber crumbs.

8. The system (200) as claimed in claim 6, wherein the crosslinked rubber is vulcanized ethylene propylene diene monomer (EPDM) and the temperature ranges from 70°C to 360° in each profile.

9. The system (200) as claimed in claim 6, wherein the twin-screw extruder includes the feed zone (210a) configured to receive the rubber granules from the conveying hopper (208), a pulverizing zone (210b) configured to mechanically shear and compress the granules between rotating screws, a devulcanizing zone (210c) configured to provide at least 13 distinct temperature profiles to break sulphur-based crosslinking bonds within the rubber, and a cooling zone (210d) configured to stabilize the devulcanized rubber and provide strip form of the devulcanized rubber at output.

10. The system (200) as claimed in claim 6, wherein the processing of dense and sponge rubber crumbs is performed separately if the rubber crumbs include both types.

Dated 9th day of July, 2025
Ankush Mahajan
Agent for the Applicant (IN/PA-1523)
OF Global Institute of Intellectual Property Pvt. Ltd.