Method of using end-of-life tire rubber crumb to produce circular rubber composition

Abstract

A method includes combining vulcanized tire rubber crumb; an activator; and at least one of virgin natural rubber, synthetic rubber, or bio-based rubber, to form a mixture; mixing until substantially homogenous; and curing the substantially homogenous mixture to form a circular rubber composition.

Description

[0001] METHOD OF USING END-OF-LIFE TIRE RUBBER CRUMB TO PRODUCE CIRCULAR RUBBER COMPOSITION

[0002] This Patent Cooperation Treaty application claims priority to U.S. Serial No. 63 / 550,160 filed on 6 February 2024 in the U.S. Patent and Trademark Office, the entirety of which is incorporated herein by reference.

[0003] FIELD OF INVENTION

[0004] The present invention is directed to a process that combines end-of-life vulcanized tire rubber crumb with an activator and at least one of virgin natural rubber, a synthetic rubber material or a bio-based rubber material to produce a circular, sustainable rubber composition or compound. The circular rubber composition can be used to produce new rubber materials, such as tires or other rubber products.

[0005] BACKGROUND OF INVENTION

[0006] Several known processes using end-of-life tires in recycling have disadvantages.

[0007] Vulcanized rubber crumb from end-of-life tires is currently used in small quantities, mainly as a filler or for the carbon black content. As the level of rubber crumb in rubber compounds or materials is increased, the physical properties may decrease significantly, as well as the performance characteristics, for example, abrasion, rolling resistance (tan delta), and the like.

[0008] In addition, the conventional wisdom in using end-of-life tires is that the rubber must first be devulcanized. This devulcanization procedure is costly and time-consuming. The devulcanization also damages the rubber by breaking part of the bonds and / or crosslinking of the rubber, thereby resulting in lower performance (e.g., abrasion, tan delta) of the material. In addition, the rubber must be re-vulcanized back into a rubber formulation with virgin rubber material. The resulting material is currently used in small quantities in tires, mainly as a filler.

[0009] Pyrolysis is used to recover carbon black and oil from end-of-life tires by subjecting them to high temperatures ranging from 500-800°C. The pyrolysis process destroys curing sites and removes cross-links, which weakens the overall cross-linking and bonds. The resulting carbon black and pyrolysis oil do not meet the necessary quality for tire treads: carbon black can only be used in limited volumes for tire side walls and pyrolysis oil cannot be used in tires. In addition, this process is not environmentally sustainable.

[0010] It would be beneficial in producing new tires with recycled rubber material to significantly reduce the amount of end-of-life tires that are landfilled, burned, or used for other low value applications, which is unsustainable and adds to global warming. It would also be beneficial to reduce the use of new virgin rubber material, thereby reducing the use of fossil fuel (for synthetic rubber) and land (for natural rubber plantations).

[0011] When putting recycled rubber into tires or other rubber products, the direct replacement of virgin material by recycled material means that virgin material is saved in equal amounts, Further, recycled rubber material can be re-recycled a significant and potentially unlimited number of times. The inventors have been successful in reusing recycled rubber as many as ten times in the lab and believe that recycled rubber can be recycled near infinitely - a circular approach.

[0012] The present invention makes use of a vulcanized rubber crumb that currently goes to waste or is used in lower grade applications to produce a new circular rubber composition, which may be used in the production of new tires that are of equal or higher quality as compared to tires made substantially with virgin rubber or to produce other rubber products. SUMMARY OF INVENTION

[0013] The invention provides in a first embodiment a method comprising combining vulcanized rubber crumb; an activator; and at least one of virgin natural rubber, synthetic rubber, or bio-based rubber, to form a mixture; mixing until substantially homogenous; and curing the substantially homogenous mixture to form a circular rubber composition.

[0014] The invention provides in a second embodiment further to any of the previous embodiments a method wherein the vulcanized rubber crumb is from end-of-life tires.

[0015] The invention provides in a third embodiment further to any of the previous embodiments a method wherein the vulcanized rubber crumb is vulcanized rubber scrap material from tire or tread manufacturing.

[0016] The invention provides in a fourth embodiment further to any of the previous embodiments a method wherein the vulcanized rubber crumb has a diameter of about 300 microns to about 500 microns. The vulcanized rubber crumb may have a diameter of equal to or less that about 425 microns.

[0017] The invention provides in a fifth embodiment further to any of the previous embodiments a method wherein the vulcanized rubber crumb comprises a cryogenic rubber crumb.

[0018] The invention provides in a sixth embodiment further to any of the previous embodiments a method wherein the activator comprises a polyolefin.

[0019] The invention provides in a seventh embodiment further to any of the previous embodiments a method wherein the activator comprises an elastomer. The invention provides in an eighth embodiment further to any of the previous embodiments a method wherein the activator comprises a trans-polyoctenamer rubber or a trans-polyacetylene rubber.

[0020] The invention provides in a ninth embodiment further to any of the previous embodiments a method wherein the at least one of virgin natural or synthetic rubber comprises natural rubber, emulsion styrene-butadiene rubber (ESBR), solution styrene butadiene rubber (SSBR), polybutadiene rubber (PBR), isobutylene rubber (HR), isoprene rubber (IR), or ethylene propylene diene monomer rubber (EPDM).

[0021] The invention provides in a tenth embodiment further to any of the previous embodiments a method wherein the bio-based rubber comprises butadiene and styrene produced by sugar cane and / or corn.

[0022] The invention provides in an eleventh embodiment further to any of the previous embodiments a method comprising combining about 90 wt.% to about 95 wt.% of vulcanized crumb rubber with about 5 wt.% to about 10 wt.% activator, based on the weight of the crumb rubber, to a masterbatch with at least one of virgin natural rubber, synthetic rubber, or bio-based rubber.

[0023] The invention provides in a twelfth embodiment further to any of the previous embodiments a method comprising about 10 wt.% to about 90 wt.% of the at least one of virgin natural rubber, bio-based rubber, or synthetic rubber, based on the weight of the circular rubber composition.

[0024] The invention provides in a thirteenth embodiment further to any of the previous embodiments a method wherein the activator is in the form of a powder.

[0025] The invention provides in a fourteenth embodiment further to any of the previous embodiments a method wherein the activator is in the form of a powder and comprises at least one of an antioxidant, oil, crumb rubber, calcium carbonate or any combination thereof.

[0026] The invention provides in a fifteenth embodiment further to any of the previous embodiments a method wherein the mixing is at ambient temperature and may reach a temperature of about 110°C to about 150°C during the mixing.

[0027] The invention provides in a sixteenth embodiment further to any of the previous embodiments a method wherein the mixture does not include devulcanzied and / or revulcanized rubber crumb.

[0028] The invention provides in a seventeenth embodiment further to any of the previous embodiments a method wherein the activator coats a surface of the vulcanized tire rubber crumb particles with a polymeric and / or elastomeric treatment, the coating creating new additional curing sites of the vulcanized rubber crumb that create crosslinks with the at least one of virgin, synthetic, or bio-based rubber material during the curing.

[0029] The invention provides in an eighteenth embodiment a circular rubber composition made by the method of any one of the previous embodiments.

[0030] An advantage of a tire produced with the circular rubber composition according to the present invention is that the tire may exhibit improved hysteresis (less rolling resistance), which results in at least one of increased mileage, improved fuel efficiency, or lower embedded CO2.

[0031] Another advantage of a tire produced with the circular rubber composition according to the present invention is that the tire may exhibit improved abrasion (less wear), which results in longer use time and lower microparticles per miles driven.

[0032] Yet another advantage of a tire produced with the circular rubber composition according to the present invention is that the rubber composition cures faster, thereby resulting in less energy used to produce tires and tire treads.

[0033] Such tires may be used for passenger cars, buses, trucks, forklifts, off-the-road vehicles, including those used in mining, agriculture, and the like, and solid tire vehicles.

[0034] BRIEF DESCRIPTION OF THE DRAWING

[0035] The sole Figure is a schematic diagram showing the proportion and composition of virgin material and differing amounts of recycled vulcanized tire rubber crumb (20%, 50%, 70%) that may be used in differing embodiments of the processes of the present invention.

[0036] DETAILED DESCRIPTION OF INVENTION

[0037] In this detailed description, references to “one embodiment”, “an embodiment”, or “in embodiments” mean that the feature being referred to is included in at least one embodiment of the invention. Moreover, separate references to “one embodiment”, “an embodiment”, or “embodiments” do not necessarily refer to the same embodiment; however, neither are such embodiments mutually exclusive, unless so stated, and except as will be readily apparent to those skilled in the art. Thus, the invention can include any variety of combinations and / or integrations of the embodiments described herein.

[0038] As used herein “substantially”, “generally”, “about”, and other words of degree are relative modifiers intended to indicate permissible variation from the characteristic so modified (e.g., ±0.1 %, ±0.5%, ±1.0%, ±2%, ±5%, ±10%, ±20%). It is not intended to be limited to the absolute value or characteristic which it modifies but rather possessing more of the physical or functional characteristic than its opposite, and preferably, approaching or approximating such a physical or functional characteristic. According to the present invention, at least one of end-of-life vulcanized tire rubber crumb or vulcanized rubber scrap material from tire or tread production is combined with an activator and at least one of virgin natural rubber, a synthetic rubber material, or a bio-based rubber material to produce a circular, sustainable rubber composition or compound.

[0039] Although the discussion below is directed to vulcanized tire rubber crumb, the present invention may be used with other types of crumb rubber (e.g., EPDM, NBR, butyl, CR). The vulcanized tire rubber crumb may contain vulcanized rubber scrap material from tire or tread production. In embodiments, the rubber crumb may be free of steel or textile contaminants. The circular rubber composition may be used to produce tires and / or may be used to produce other rubber products (e.g., roofs, gaskets, and the like).

[0040] In embodiments, the vulcanized tire rubber crumb may have a diameter of about 300 to about 500 microns, for example about 425 microns (about 40 mesh to about 120 mesh). In specific embodiments, the vulcanized tire rubber crumb may comprise a mixture of crumb equal to or smaller than about 425 microns. The vulcanized tire crumb rubber may have a specific gravity of about 1 .1 to about 1 .2. The vulcanized rubber crumb may be cryogenic or non-cryogenic.

[0041] In embodiments, cryogenic rubber crumb is produced in a process where ambient rubber crumbs (e.g., of about 10 mesh size) are frozen and crushed into a powder. The crumbs may then be filtered. The fracturing of the rubber crumb in the cryogenic process releases contaminants (such as textile residue) which are removed to create a very pure product. This cryogenic grinding process creates a rubber crumb surface that may have better cross-links with at least one of a virgin, synthetic, or bio-based rubber material, as compared to a mechanically ground rubber crumb of the same mesh size.

[0042] According to the present invention, in specific embodiments, the activator may be CRs™, commercially available from Circular Rubber Solutions, LLC of Miami Beach, Florida. In an embodiment, the activator may comprise a polymer, including but not limited to, a polyolefin and / or an elastomer. In an embodiment, the activator may include, but is not limited to, a trans-polyoctenamer rubber or a trans-polyacetylene rubber (a metathesis polymer of cyclooctene with prevalently trans-isomeric double bonds). The activator may be in the form of a powder. In embodiments, the powder may contain additional components or ingredients including, but not limited to, at least one of oil, crumb rubber, calcium carbonate, or any combination thereof.

[0043] In embodiments, virgin natural rubber and / or synthetic rubber may include, but is not limited to, natural rubber, emulsion styrene-butadiene rubber (ESBR), solution styrene butadiene rubber (SSBR), polybutadiene rubber (PBR), isobutylene rubber (HR), isoprene rubber (IR), ethylene propylene diene monomer rubber (EPDM), and the like. In embodiments, a bio-based rubber may include, but is not limited to bio-based butadiene and styrene produced by sugar cane and / or corn. The sole Figure is a schematic diagram showing the proportion and composition of virgin material and differing amounts of recycled vulcanized tire rubber crumb (20%, 50%, 70%) that may be used in embodiments of the processes of the present invention.

[0044] In an embodiment, about 90 wt.% to about 95 wt.% of vulcanized tire rubber crumb is combined with about 5 wt.% to about 10 wt.% of the activator or a powder comprising the activator, based on the weight of the crumb rubber, to a masterbatch containing at least one of virgin natural, synthetic rubber or bio-based rubber in standard mixing equipment. The mixture is mixed until substantially homogenous. In specific embodiment, the mixing may be about 2 to about 5 minutes depending on any temperature increase in the mixer (e.g., Banbury mixer).

[0045] The substantially homogeneous mixture is then cured to obtain a circular rubber composition. In specific embodiments, a standard curing package may be used. The curing package may include at least one of TBBS (N-tert-butyl-benzothiazole sulfonamide), DMTD, antioxidants, or any combination thereof. In a specific embodiments, a curing package may be added to the mixture in at least one of the second or third pass of the mixing at a temperature of less than about 190°C. By using the activator according to the present invention, curing may be about 10-15% faster than standard curing, which may decrease electricity usage and / or increases capacity of the mixer. The curing time may be adjusted depending on the amount of vulcanized tire crumb rubber and / or at least one of virgin, synthetic, or bio-based rubber.

[0046] The least one of virgin natural, synthetic rubber, or bio-based rubber may comprise about 5 wt.% to about 90 wt.%, for example about 10 wt.% to about 90 wt.% or about 20 wt.% to about 90 wt.%, of the resulting circular rubber composition.

[0047] According to the present invention, in embodiments, the activator coats the surface of the vulcanized tire rubber crumb particles with a polymeric and / or elastomeric treatment deposited on the rubber crumb surface. The coating creates new additional curing sites and these new curing sites of the vulcanized rubber crumb are used to create new cross-links with the at least one of virgin, synthetic, or bio-based rubber material during curing.

[0048] The circular rubber composition according to the present invention comprises a substantially fully-cured, cross-linked composition or compound containing at least one of virgin, synthetic rubber or bio-based rubber and the polymeric and / or elastomeric surface-treated vulcanized tire rubber crumb. In embodiments, additional components may include, but are not limited to, at least one of carbon black, silica, or other rubber chemicals that come from the vulcanized tire crumb rubber.

[0049] The following are non-limited embodiments relating to the mixing and milling used in an exemplary, non-limiting processes according to embodiments of the present invention.

[0050] A. Standard Mixing

[0051] Rubber compounders for tire carcasses and treads may consist of natural (NR), synthetic butadiene rubber (SBR), peptisers, carbon black and / or silicas, non carbon black fillers, zinc oxide, fatty acids, processing aids, antioxidants, and vulcanizing indigents such as accelerators, etc.

[0052] Most tire manufacturers and rubber compounders use a one or two pass mixing process to produce tire compounds in a Banbury or tangential mixer.

[0053] For a one pass mixing process, a premix masterbatch of activator and cryogenic rubber crumb, virgin polymer raw material, and curing package are added at the same time into a Banbury mixer. The mixing duration may be 10-20% shorter due to the vulcanized rubber crumb from the end-of-life tires (ELT).

[0054] For a two-pass mixing process, a premix of activator and cryogenic recycle rubber crumb masterbatch is added to the mixer along with the corresponding SBR, NR, CB / silica, oil and is mixed until the temperature reaches 190°F or 90°C. The mixing or mastication result is a homogenous polymer compound.

[0055] In the second pass, a curing package comprising accelerator, antioxidant, and other ingredients are added and mixed for 2-3 minutes. The temperature should not exceed 100°C. This final mastication results in a cured rubber compound that is ready for processing.

[0056] B. Cryogenic Mixing Process

[0057] A masterbatch comprising cryogenic rubber crumb may be treated as a replacement rubber material for virgin material. The masterbatch comprises 5% activator (CRs™ from Circular Rubber Solutions LLC) and 95% cryogenic micronized rubber crumb (minimum 40 mesh / 425 microns with a tail of smaller size crumbs).

[0058] The cryogenic process uses liquid nitrogen at -190°C to freeze (4-6 mm) ambient rubber crumb and systemically shatters the rubber crumb into 40 mesh and smaller size crumbs. This shattering process releases textile and other impurities that remain in the ambient rubber crumb resulting in a high quality polymer product.

[0059] The cyrogenic micronized crumb is added to a high shear cyclomixer (e.g., 430 kg / m3) mixing vessel with the activator at a 95:5 ratio. Through the high velocity mixing process the activator fully coats the cryogenic micronized rubber crumb and re-activates it, creating additional curing sites in the masterbatch compound.

[0060] C. Milling

[0061] The mill nip which is distance between the front roller to last roller may have to be adjusted increasing or decreasing the distance using the levers on the mill, depending on the mixture and the amount of rubber crumb and / or polymeric activator. A higher rubber crumb content may decrease the green strength and can result in sagging. A lower tear strength and sagging can be solved by decreasing the mill nip.

[0062] D. Properties of the Circular Rubber Composition

[0063] In a specific embodiments, the obtained circular rubber composition may have the following properties:

[0064] Tensile range, psi: 2,500-3,000

[0065] Elongation range: 350-440

[0066] Tan Delta Amplitude sweep

[0067] - at 0.1 % Oscillation strain: Tan(delta) is0.136-0.147

[0068] - at 1 % Oscillation strain: Tan(delta) is 0.178-0.198

[0069] - at 10% Oscillation strain: Tan(delta) is 0.225-0.257

[0070] Tan Delta Frequency sweep

[0071] - at 0.1 rad / s Angular Frequency co: Tan(delta) is 0.157-0.186

[0072] - at 1 rad / s Angular Frequency co: Tan(delta) is 0.154-0.177 - at 10 rad / s Angular Frequency co: Tan(delta) is 0.171-0.197

[0073] - at 100 rad / s Angular Frequency co: Tan(delta) is 0.190-0.209 The measurements were made according to ASTM standards.

[0074] In an embodiment, the circular rubber composition may be used to produce tires, which in specific embodiments have tires and treads that perform about 10% to about 20% better than tires produced substantially (e.g., with about 100%) virgin rubber material.

[0075] Further, tire tests in commercial long-haul bus traffic showed 10% less wear for tires made with the circular rubber composition of the present invention compared to tires made without the circular rubber composition over a tire life cycle of up to 123,000 kilometers.

[0076] INDUSTRIAL APPLICABILITY

[0077] According to the present invention, end-of-life vulcanized tire rubber crumb is combined with an activator and at least one of virgin natural rubber, a synthetic rubber material, or a bio-based rubber material to produce a circular, sustainable rubber composition. The circular rubber composition may be used to produce tires or other rubber products.

[0078] Although the present invention has been described in terms of particular exemplary and alternative embodiments, it is not limited to those embodiments. Alternative embodiments, examples, and modifications which would still be encompassed by the invention may be made by those skilled in the art, particularly in light of the foregoing teachings.

[0079] Those skilled in the art will appreciate that various adaptations and modifications of the exemplary and alternative embodiments described above can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims

WHAT IS CLAIMED IS:

1. A method, comprising: combining vulcanized rubber crumb; an activator; and at least one of virgin natural rubber, synthetic rubber, or bio-based rubber, to form a mixture; mixing until substantially homogenous; and curing the substantially homogenous mixture to form a circular rubber composition.

2. The method of Claim 1 , wherein the vulcanized rubber crumb is from end-of-life tires.

3. The method of Claim 1 , wherein the vulcanized rubber crumb is vulcanized rubber scrap material from tire or tread manufacturing.

4. The method of Claim 1 , wherein the vulcanized rubber crumb has a diameter of about 300 microns to about 500 microns.

5. The method of Claim 1 , wherein the vulcanized rubber crumb has a diameter of equal to or less that about 425 microns.

6. The method of Claim 1 , wherein the vulcanized rubber crumb comprises a cryogenic rubber crumb.

7. The method of Claim 1 , wherein the activator comprises a polymer.

8. The method of Claim 1 , wherein the activator comprises a polyolefin.

9. The method of Claim 1 , wherein the activator comprises an elastomer.

10. The method of Claim 1 , wherein the activator comprises a trans-polyoctenamer rubber or a trans-polyacetylene rubber.11 . The method of Claim 1 , wherein the at least one of virgin natural or synthetic rubber comprises natural rubber, emulsion styrene-butadiene rubber (ESBR), solution styrene butadiene rubber (SSBR), polybutadiene rubber (PBR), isobutylene rubber (HR), isoprene rubber (IR), or ethylene propylene diene monomer rubber (EPDM).

12. The method of Claim 1 , wherein the bio-based rubber comprises butadiene and styrene produced by sugar cane and / or corn.

13. The method of Claim 1 , comprising combining about 90 wt.% to about 95 wt.% of vulcanized crumb rubber with about 5 wt.% to about 10 wt.% activator, based on the weight of the crumb rubber, to a masterbatch with at least one of virgin natural rubber, synthetic rubber, or bio-based rubber.

14. The method of Claim 13, comprising about 10 wt.% to about 90 wt.% of the at least one of virgin natural rubber, bio-based rubber, or synthetic rubber, based on the weight of the circular rubber composition.

15. The method of any one of Claims 1 -13, wherein the activator is in the form of a powder.

16. The method of Claim 15, wherein the powder further comprises at least one of an antioxidant, oil, crumb rubber, calcium carbonate or any combination thereof.

17. The method of any one of Claims 1 -13, wherein the mixing is at ambient temperature and may reach a temperature of about 110°C to about 150°C during the mixing.

18. The method of any one of Claims 1-13, wherein the mixture does not include devulcanzied and / or re-vulcanized rubber crumb.

19. The method of any one of Claims 1-13, wherein the activator coats a surface of the vulcanized tire rubber crumb particles with a polymeric and / or elastomeric treatment, the coating creating new additional curing sites of the vulcanized rubber crumb that create cross-links with the at least one of virgin, synthetic, or bio-based rubber material during said curing.

20. The method of any one of Claims 1-13, wherein the mixing is in a high shear mixer. 21 . A circular rubber composition made by the method of any one of Claims 1 -13.

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