Thermoplastic vulcanizate and method of making same

Abstract

A thermoplastic vulcanizate precursor composition comprises crosslinkable devulcanized rubber and one or more polyolefins. Upon crosslinking the devulcanized rubber a thermoplastic vulcanizate is formed. The crosslinkable devulcanized rubber is formed by using devulcanization aid and shear energy.

Description

THERMOPLASTIC VULCANIZATE AND METHOD OF MAKING SAMEBACKGROUND OF THE INVENTION1 . Field of the Invention

[0001] The present invention relates to a thermoplastic vulcanizate and a method of making same.2. Discussion of Background Information

[0002] Thermoplastic vulcanizates (TPVs) typically are dynamically vulcanized alloys consisting mostly of frilly cured rubber particles (usually EPDM = Ethylene Propylene Diene Monomer) dispersed in a thermoplastic matrix, often polypropylene (PP). They are part of the thermoplastic elastomer (TPE) family of polymers but are closest in elastomeric properties to EPDM thermoset rubber, combining the characteristics of vulcanized rubber with the processing properties of thermoplastics. There are many different grades of TPVs, which are used globally in the automotive, household appliance, electrical, construction, and healthcare markets.

[0003] In producing the commonly used TPVs uncured EPDM rubber is ground, blended with PP, fillers and additives and introduced into a twin screw extruder. Under melt processing, the continuous phase melts and flows, but the discrete uncrosslinked rubber phase remains in a separate domain and is broken into ever smaller particles. It is carried with the flow of the thermoplastic phase under meh processing. The resultant mixture has a microstructure of a discrete elastomer phase in a continuous thermoplastic material. Once the microstructure is developed a crosslinker is introduced and the elastomer phase starts to crosslink. This is commonly done with resole resin and stannous chloride, but other crosslinking agents such as peroxides and sulfur can also be used.

[0004] Since a continuous thermoplastic domain is required for melt processing, it is important that the discrete and continuous phases are developed before the rubber is crosslinked (and remain at least partially discrete after crosslinking), the risk being that the rubber crosslinks to a non-melt processable elastomer before the domains are formed. This could lead to poor product quality, or rubber domains that crumb to dust. In the Avorst case, the rubber crosslinks and locks up the compounding equipment. Once the crosslinking is complete, the TPV is typically vacuum stripped, and the polymer is pelletized and ready for sale.

[0005] It would be advantageous to have available a TPV in which at least some of the materials used for the production thereof and, in particular, the rubber component thereof, are derived / sourced from materials that have already been used and can be recycled instead of becoming a part of a landfill.SUMMARY OF THE INVENTION

[0006] The present invention provides a thermoplastic vulcanizate precursor composition which comprises (i) crosslinkable devulcanized rubber and (ii) one or more polyolefins.

[0007] In one embodiment of the composition, particles of component (i) are dispersed in a mixture which comprises component (ii).

[0008] In another embodiment, at least a part of component (i) is derived from already used rubber (recycled rubber). For example, at least a part of (i) may be derived / sourced from rubber of end-of-life tires.

[0009] In another embodiment, component (i) has been produced by using one or more devulcanization aids as well as shear energy to dcvulcanizc a vulcanized (crosslinked) rubber.

[0010] In another embodiment, component (ii) comprises one or more of polypropylene, polyethylene (e.g., high density polyethylene, HDPE), propylene-ethylene copolymers and polyethylene modified with one or more C4, C6 and / or C8 olefins.

[0011] In another embodiment of the composition, at least a part of component (ii) is recycled material.

[0012] In another embodiment, the composition comprises at least 10 % by weight of component (i) and''or at least 20 % by weight of component (ii), based on the total weight of the composition.

[0013] In another embodiment, the weight ratio of component (i) and any other optionally present crosslinkable components present in the composition to the one or more polyolefins of component (ii) is from 5 : 1 to 1 : 5.

[0014] In another embodiment, the composition further comprises paraffinic oil and / or aromatic oil and / or one or more processing aids and / or one or more vulcanization accelerators and / or one or more crosslinking agents. The one or more crosslinking agents may, for example, be selected from one or more of sulfur, peroxides, and resole resins.

[0015] The present invention also provides a thermoplastic vulcanizate composition in which component (i) and any other optionally present crosslinkable (rubber) components present in the precursor composition set forth above (including the various embodiments thereof) have been subjected to at least partial (and preferably substantially complete) crosslinking.

[0016] In one embodiment of the vulcanizate composition, the crosslinkable rubber components present in the precursor composition set forth above have at least partially (and preferably substantially completely) been crosslinked by one or more crosslinking agents and / or by radiation. The crosslinking radiation may, for example, be one or more of UV, electron beam, gamma, and laser radiation.

[0017] In another embodiment, the composition is present in the form of granules and / or pellets.

[0018] The present invention also provides an article which comprises or consists of the thermoplastic vulcanizate composition set forth above.

[0019] Also provided by the present invention is a method of producing the thermoplastic vulcanizate composition set forth above. The method comprises extruding a mixture which comprises components (i) and (ii) as set forth above and any other optionally present crosslinkable rubber components and at least one crosslinking agent at an elevated temperature which is sufficient to at least partially crosslink the crosslinkable (vulcanizable) rubber components.

[0020] The present invention also provides a crosslinkable devulcanized rubber for use in the thermoplastic vulcanizate precursor composition set forth above. The dcvulcanized rubber is produced by using one or more devulcanization aids and preferably also shear energy for devulcanizing a vulcanized rubber, provided, for example, by a twin-screw extruder and / or a two-roll mill.

[0021] In one embodiment, the one or more dcvulcanization aids comprise zinc oxide or a transition metal salt, such as, e.g., an acetate of a transition metal metal salt (e.g., Cu, Zn, Mn or Fe), preferably zinc acetate.

[0022] The present invention also provides a method of producing the crosslinkable devulcanized rubber set forth above. The method comprises contacting vulcanized rubber with a dcvulcanization aid, followed by subjecting the vulcanized rubber to shear.DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

[0023] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

[0024] As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. For example, reference to “a rubber” would also mean that combinations of two or more rubbers can be present unless specifically excluded.

[0025] Except where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, etc. used in the instant specification and appended claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding conventions.

[0026] Additionally, the disclosure of numerical ranges within this specification is considered to be a disclosure of all numerical values and ranges within that range. For example, if a range is from I to 50, it is deemed to include, for example, 1, 7, 34, 46. 1, 23.7, or any other value or range within the range.

[0027] The various embodiments disclosed herein can be used separately and in various combinations unless specifically stated to the contrary.

[0028] As set forth above, the present invention provides inter alia, a thermoplastic vulcanizate precursor composition which comprises (i) crosslinkable devulcanized rubber and (ii) one or more polyolefins. The one or more polyolefins will often include one or more elastomeric polyolefins but other polyolefins are suitable as well. Non-limiting examples of suitable polyolefins include polypropylene / polyethylene (PP / PE), polypropylene (including isotactic, atactic and syndiotactic PP) and polyethylene modified with C4, C6 or and / or C8 olefins.

[0029] Particles of component (i) and any other optionally present crosslinkable rubber components (e.g., non-crosslinked EPDM rubber) present in the precursuor composition are preferably dispersed in a mixture which comprises component (ii). The mixture which comprises component (ii) may comprise various other components in addition to component (ii). For example, the mixture preferably comprises one or more aliphatic (paraffinic) and / or aromatic oils, particularly one or more aliphatic oils, often in a concentration of from 1 % to 30 % by weight, e.g., from 8 % to 25 % by weight, based on the total weight of the mixture. The mixture may also contain various other components such as antioxidants, processing aids, vulcanization accelerators, colorants, fillers (e.g., one or more of the many fillers known for use in thermoplastic vulcanizate compositions, examples of which include mineral fillers like calcium carbonate, talc, mica, clay, wollastonite, etc.), odor suppressants, crosslinking agents. Some of these other components may be present already initially whereas others such as, e.g., crosslinking agents may be added to the mixture only at a later stage, e.g., after component (i) has been combined with the mixture. The other components together will usually be present in a total concentration not exceeding 15 % by weight, e.g., not exceeding 10 % y weight, based on the total weight of the mixture.

[0030] Component (ii) will often be present in the mixture in a concentration of from 60 % to 95 % by weight, based on the total -weight of the mixture. Component (ii) may be present as a mixture / blend of two or more polyolefins, which preferably comprise polypropylene. Examples of constituents of component (ii) in addition to polypropylene include polyethylene (e.g., high density polyethylene, HDPE) and propylene-ethylene copolymers. Modified olefin polymers and copolymers may be used as well. At least a part of component (ii), e.g., at least 10 %, at least 20 %, at least 30 %, at least 40 %, at least 50 %, at least 60 %, at least 70 %, atleast 80 %, at least 90 %, at least 95 % by weight or even about 100 % by weight of component (ii) may be recycled material.

[0031] Also at least a part of component (i) may be derived from already used rubber (recyclable rubber). For example, at least 10 %, at least 20 %, at least 30 %, at least 40 %, at least 50 %, at least 60 %, at least 70 %, at least 80 %, at least 90 %, at least 95 % by weight or even about 100 % by weight of component (i) may be derived / sourced from already used (recycled) rubber such as rubber of end-of-life tires.

[0032] Component (i) will usually be present in the thermoplastic vulcanizate precursor composition of the present invention in a concentration of at least 10 % by weight, e.g., at least 20 %, at least 30 %, at least 40 %, at least 50 % or at least 60 % by weight but usually not higher than 70 % by weight, based on the total weight of the composition. If the precursor composition also contains virgin uncrosslinked robber, i.e., robber that has never been crosslinked before (e.g., EPDM rubber), the above concentrations apply to the total of all crosslinkable robber components in the composition. Preferably at least 50 % by weight, e.g., at least 60 %, at least 70 %, at least 80 %, at least 90 % or at least 95 % by weight of the crosslinkable components in the composition is previously devulcanized rubber. Of course, substantially all of the crosslinkable (rubber) components in the composition may be previously devulcanized robber.

[0033] Component (ii) will often be present in the thermoplastic vulcanizate precursor composition of the present invention in a concentration of at least 30 %, e.g., at least 35 %, at least 40 %, or at least 45 % by weight, but usually not higher than 70 % by weight, e.g., not higher than 60 % by weight, based on the total weight of the composition.

[0034] The weight ratio of component (i) and the other optionally present crosslinkable components to the one or more elastomeric polyolefins of component (ii) will often be from 5 : 1 to 1 : 5, e.g., from 4 : 1 to 1 : 4, from 3 : 1 to 1 : 3, or from 2 : 1 to 1 : 2.

[0035] The thermoplastic vulcanizate precursor composition of the present invention may optionally also comprise vulcanized robber particles, e.g., particles of non-devulcanized rubber such as crumb robber (traditional reclaimed robber) obtained from, e.g., end-of-life tires. In this case the above weight ratio includes the non-devulcanized rubber in component (i). If non-devulcanized rubber is present the weight ratio of dcvulcanizcd rubber to non-devulcanizcd rubber in the thermoplastic devulcanized precursor composition is preferably from 20 : 1 to 1 : 1, e.g., from 10 : 1 to 1 : 1, from 5 : 1 to 1 : 1, or from 3 : 1 to 1 : 1.

[0036] To obtain the thermoplastic vulcanizate composition of the present invention, component (i) and the optionally present additional crosslinkable ( rubber) components of the precursor composition are at least partially crosslinked by one or more crosslinking agents (e.g., for free radical crosslinking) and / or by radiation, for example by one or more of UV, electron beam, gamma and laser radiation. Non-limiting examples of suitable crosslinking agents include sulfur, peroxides and resol resins, but any of the crosslinking agents which are known for the crosslinking of rubber can be used.

[0037] One method of producing the thermoplastic vulcanizate composition of the invention comprises extruding a mixture which comprises components (i) and (ii) as set forth above and at least one crosslinking agent at an elevated temperature (e.g., at least 150°C) which is sufficient to at least partially crosslink component (i) and any other optionally present crosslinkable (rubber) components in the mixture. If radiation such as electron beams or laser beams is used for crosslinking the crosslinking agent(s) can usually be dispensed with, although a combination of crosslinking agent(s) and radiation may also be used.

[0038] The method may be carried out, for example, by feeding all components together into a twin-screw extruder / reactor at the beginning. Alternatively, in a first step select components may be added to the twin-screw extruder / reactor and blended at the beginning and the remaining components (such as crosslinking agents, accelerators and promoters) are then added in a second step to complete the crosslinking. This can be done in a number of ways, including side stuffing, liquid addition or use of an additional extruder, for example.

[0039] According to the invention, the crosslinkable devulcanized rubber for use as component (i) in the thermoplastic vulcanizate precursor composition set forth above may be produced by using one or more dcvulcanization aids and preferably also shear energy, provided for example, by a twin-screw extruder and / or a two-roll mill for devulcanizing a vulcanized rubber.

[0040] All of the known dcvulcanization aids may be used for this purpose, non-limiting examples whereof include zinc oxide and acetates of transition metals such as Cu, Zn, Mn andFe. Additional examples of suitable devulcanization aids are listed in, e.g., Table 7.1.2. of “Tire Waste and Recycling”, published by Academic Press Elsevier, 2021, in Chapter 7 (Regeneration and Devulcanization), the entire disclosure of which is incorporated by reference herein.

[0041] The present invention also provides a method of producing the crosslinkable de vulcanized rubber set forth above. The method comprises contacting vulcanized rubber with a dcvulcanization aid, followed by subjecting the vulcanized rubber to shear (provided, e.g., by a twin-screw extruder and / or or a two-roll mill).

[0042] There are few sustainable options for TPVs. The approach set forth above allows for both phases (dispersed rubber phase and continuous thermoplastic phase) of the TPV to be derived from recycled content, allowing for potentially very high recycled content. Since tires are post-consumer, this approach provides for a higher content of post-consumer recycle content which is favored by the market. There is potential for economic advantages as well; the rubber phase of TPVs is typically derived from EPDM, which comes at a significant cost premium compared to the devulcanized rubber.EXAMPLES

[0043] The following examples are provided for illustrative purposes only and are in no way to be construed as limiting the scope of the present invention, which is solely defined by the appended claims.Preparation of crosslinkable devulcanized rubber derived from end-of-life tire rubber (Polymer A)

[0044] Polymer A is prepared via a two-step process. The first process step is to coat rubber particles with a dcvulcanization aid and in this example this includes:1. Providing crumb rubber in the form of a 30 mesh ground tire rubber (GTR) produced from end of life tires (other sources and mesh sizes can be used as well).2. Coating the GTR with a 20% aqueous zinc acetate (ZnAc) solution and processing it through a gentle twin screw mixer to work the ZnAc into the rubber surface. A typ ical addition rate of ZnAc is 2.5 % on a dry basis (calculated as dihydrate).The ZnAc-coated GTR is fed into a fluidized bed dryer, w’here its moisture content is reduced to below 0.5 %.3. In the second process step this dried intermediate is subjected to mechanical energy (shear). For this purpose, a twin-screw extruder with a screw profile designed to shear the intermediate material into a completed devulcanizate may be used. Key variables in controlling the amount of mechanical energy applied include feed / production rate, screw profile, screw rotational speed, temperature profile (from heating / cooling and heat generated by shear). The energy consumed (percent torque of the motor) is monitored and the specific energy applied to the material (kWh / kg, for example) is calculated. The resultant product is Polymer A.

[0045] By adjusting the amount and type of de vulcanization aid in the first step as well as by adjusting the mechanical aspects of screw configuration / profile, screw rotational speed, feed rate and temperature profile in the second step one the resulting polymer can be fine-tuned to the target application.Curing Polymer A with Sulfur as Crosslinking Agent

[0046] In the formulations set forth in Table 1 below a standard cure package containing varying amounts of sulfur is added to Polymer A. Components were blended in a kneader mixer, sheeted on a rubber mill and cured 10 minutes at 160° C. Polymer A by itself does not show reactivity and does not form an elastomer with any mechanical properties under cure conditions. However, Polymer A with a typical cure package and increasing levels of sulfur shows indication of cure and phy sical property development. At a sulfur level of 3 phi- straight Polymer A shows about 40% of the physical properties obtained with a 100% virgin synthetic rubber cured using a similar cure package under similar cure conditions.Table 1: Stepwise Addition of Sulfur

[0047] In a second series (summarized in Table 2 below; components blended in a kneader mixer, sheeted on a rubber mill and cured 10 minutes at 160° C.) “neat” Polymer A was vulcanized with 2 phr sulfur (note - to 100 parts Polymer A. . .previous study was to 160 parts Polymer A) and varying the concentration of accelerator ((Benzothiazyl-2-Dicyclohexyl Sulfenamide - DCBS). While the elastomers in this series were still cured at 160° C, the RPA kinetic data of this series was performed at a slightly higher temperature of 190° C, which is more in line with the temperature required to compound them with polypropylene and therefore a better indicator of the cure kinetics one would expect in TPV processing conditions.Table 2 : Stepwise Addition of AcceleratorCTP = N-(Cyclohexylthio) Phthalimide

[0048] The data in Table 2 show that Polymer A can be cross! inked with the addition of sulfur and without the addition of accelerator (in this case DCBS). Slight addition of DCBS did improve physical properties (especially tensile properties), but further addition had diminishing returns.

[0049] From the data set forth in Table 1 and Table 2 the following can be concluded:1 . Polymer A requires the addition of sulfur to cure; the devulcanization process described above renders any remaining residual sulfur in the starting cured rubber unreactive.2. Polymer A can be cured with sulfur and no accelerator added, suggesting that at least some of the accelerators survive the devulcanization process described above.3. Physical properties increase with increasing additions of sulfur, though with diminishing returns going from 2 phr to 3 phr.4. Stepwise increase of accelerator shows that onset of cure is not affected, but speed of cure (T90) accelerates. Tensile properties improve with increasing accelerator concentration.

[0050] As these materials are used for the production of TP Vs, there are a few key considerations. The continuous phase is usually polypropylene, which requires a processing temperature of typically 190° C. Further, depending on twin screw extruder configuration and feeding factors, residence time in a typical screw is short, often less than 2-3 minutes (depending on conditions). If the reaction is too fast, there is a risk that the compound will not have a chance to create the discrete rubber domains before curing. If the reaction is too slow, there is a risk that the TPV will be under- cured and post-curing might be required to achieve maximum physical properties. Cure kinetics at both 160° C and 190° C were studied. Increasing the cure temperature from 160° C to 190° C decreases cure (T90 - the time it takes in minutes to get 90% cure as measured by RPA torque) from 12.8 min to about 1.65 min. This suggests that processing to a TPV at 190° C would still be feasible with 2 phr sulfur and 1.2 phr curative, though it would be prudent to walk up the sulfur and curatives cautiously to avoid locking up the compounder with cured rubber compound.

[0051] To demonstrate the technology on a small scale, one potential route to sulfur cured TPV is to cold mix curatives and sulfur in a kneader mixer. Mixing time is kept short enough so that the material is still free flowing. Then the additional additives needed (as outlined in the Polymer A section) are preblended as follows:• Add oil and mix. (Can add processing aids, antioxidants and odor masks at this phase).• Add polypropylene and thermoplastic polyolefin and mix.• Compound as usual, walking up the production rate and monitoring processing torque to assure no issues are developing.Curing Polymer A via free radical polymerization by addition of peroxide

[0052] A second method to cure Polymer A that is useful for the production of TPVs is via free radical polymerization by the addition of peroxide. For this study dicumyl peroxide (Perkadox BC-FF from Nourvon ), was used as curative.The half-life properties of dicumyl peroxide are as follows:10 hour half-life - 112° C1 hour half-life - 132° C0.1 hour half-life - 154° C.

[0053] To produce a TPV where the continuous phase is polypropylene the material will need to be processed at 190° C; this peroxide was selected due to the half-life and cure kinetics it would provide but other peroxides may be better suited depending on the compounding conditions required by the continuous phase.

[0054] To evaluate peroxide crosslinking of Polymer A, peroxide was blended into Polymer A (i) neat, (ii) dissolved in an aromatic oil and (iii) dissolved in paraffinic oil. These oils readily absorb into Polymer A, and it was thought that the oil might help to better distribu te / penetrate the peroxide into Polymer A, but the results suggest that the oil was not required. Table 3 below show’s the results obtained with Polymer A cured with four levels of peroxide under each of these conditions.Table 3: Crosslinking Polymer A with Dicumyl Peroxide at 160 °C

[0055] From the data in Table 3 (and comparing them to those in Table 1 and Table 2) it can be seen that peroxide cure yields an elastomer with lower tensile properties than a sul fur-cured product. At a temperature of 160° C the reaction time was too slow (as measured by T(90)). Wien tested at 190° C, the Polymer A / peroxide system provided cure times appropriate for simple evaluation as a TPV produced in simple twin screw compounding.

[0056] The obtained data suggests that the addition of oil as a carrier of peroxide is not required or desired, and the extra oil reduced both hardness and strength properties of the resultant polymers. Additional peroxide did reduce cure time slightly but did improve tensile properties.

[0057] Besides the obvious safety issues in handling peroxides, there are a few’ considerations when using peroxide curing into TPVs. First, peroxide cures start rapidly at high temperatures. It could prove beneficial to side stuff or deliver the peroxide in liquid / molten form into the twin screw once the microstructure has been formed. Second, peroxide cure might have residual VOC that needs to be addressed, for example by applying a vacuum.

[0058] Finally, peroxides are commonly used to “vise break” polypropylene (the peroxide attacks and cleaves the PP backbone, reducing molecular weight and improving flow characteristics). For polyethylene, the opposite happens; the peroxide causes crosslinking in the PE backbone, increasing branching and molecular weight while decreasing melt flow characteristics. This secondary effect on the olefin continuous phase may lead to confounding results.Curing Polymer A via crosslinking by the addition of resole resins with a catalyst

[0059] Crosslinking rubber with resole resins is well known in the literature (see, e.g., U.S. Patent No. 3,000,847, the entire disclosure of which is incorporated by reference herein), both for rubber and TPVs. It is believed that one of the most common methods of production of EPDM-based TPVs is via crosslinking with resole type resins, such as a methylol- terminated phenol formaldehyde resin based on para-octylphenol.

[0060] The benefit of using resole chemistry is that the curing reaction is not expected to take place without the catalyst (commonly stannous chloride, though literature suggests that zinc oxide or halogen donors such as halogenated resins could act as catalysts as well). Also, the crosslinking forms two bonds with the rubber chain on each side of the resole resin, leading to a stronger, more stable elastomer. Resole chemistry can be practiced in conjunction with sulfurbased vulcanization or peroxide chemistry, providing hybrid solutions.

[0061] In making a TPV, resole may offer some processing advantages. By requiring a catalyst to start / drive cure a rubber / olefm / resole microstructure can be developed before the catalyst is introduced. Second, the literature suggests that resole resin, with its four connections per molecule might offer better performance than sulfur or peroxide curatives. On the downside, resole resin might require additional drying of the resultant TPV.Production of TPV via crosslinking Composition B with peroxide

[0062] To demonstrate that crosslinking the rubber phase of a TPE is possible, a scheme was devised to introduce peroxide into a pre-compounded Composition B. Composition B had the following composition:Commercially available from ERGON Inc. as Omniprene A122Tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]hexane3Tris(2,4-di-tert-butylphenyl)phosphite4Isotactic PP with random PE, MFI 21, Shore A 71 , commercially available from ExxonMobil as Vistamaxx 65025Low viscosity isotactic PP with random PE, Shore C 53 Commercially available from ExxonMobil as Vistamaxx 8880

[0063] For this test, Composition B was prepared on a commercial scale and was provided in the form of plastic pellets typically used in injection molding.

[0064] To introduce the peroxide into Composition B, Perkadox BC-FF (dicumyl peroxide) was mixed with paraffinic oil as set forth below and the mix of oil and peroxide was blended with Composition B pellets via mechanical mixing (stirring / tumbling).

[0065] The addition rate of peroxide was based on the total recycled rubber content of the polymer. Composition B is 50% recycled devulcanized rubber (after accounting for the ZnAc), thus an application rate of 0.12 % in the mixture is equivalent to an application rate of 0.25 % on a rubber basis, and an application rate of 0.25 % in the mixture is equivalent to 0.50 % on a rubber basis. The oil readily absorbed into Composition B, assuring even mixing and distribution of the peroxide on / near the surface of the pellets.

[0066] It was anticipated that the incorporation of more oil into Composition B would change the physical and molding properties of the TPV (plasticizing the compound, making the elastomer softer and weaker, while increasing melt flow), and accordingly a sample that contains oil but no peroxide was also included in the study to allow for a fair comparison.Table 4: Formulation and Properties of TPV Based on Peroxide Cure of Composition BPOST CURE

[0067] Once the oil / peroxide mixture was well absorbed, the pellets were fed into a twin-screw extrader and processed at 190° C to initiate and drive polymerization. The microstructure (rubber domains in continuous olefin) was already in place before the second processing took place, and this second processing was intended to only mix the peroxide into the compound and trigger the creation of free radicals to initiate the crosslinking reaction.

[0068] Comparing the base Composition B to Composition B with added oil, it can be taken from Table 4 that Shore A hardness decreases (the material softened / plasticized), flow properties increase as measured by melt flow index and spiral flow, and mechanical properties (tensile, tear and elongation) all decrease - all as expected. Comparing Composition B with oil to the two samples with increasing peroxide content (Examples 1-3), the addition of peroxidedecreased flow characteristics (as measured by MFI and spiral flow) and increased / improved physical properties (tensile, tear, elongation) markedly. Hardness as measured by Shore A did not change with the addition of peroxide in this case.

[0069] As mentioned above, peroxide can be added to polypropylene systems to “vise break” the material (cleave the PP chains to improve melt characteristics, at the cost of physical properties). In this data set the opposite occurred; increasing mechanical properties and decreasing flow properties are what would be expected by crosslinking an uncured rubber domain, confirming that a TPV was produced.

[0070] In this study, residence time in the lab scale twin screw extruder was short; to test if the reaction was near completion the material was post cured for one hour at 160° C and retested for physical properties. Post-curing did not improve properties and it thus, is believed that cure was near completion in the extrusion process.

Claims

CLAIMS:

1. A thermoplastic vulcanizate precursor composition, wherein the composition comprises (i) crosslinkable devulcanized rubber and (ii) one or more polyolefins.

2. The composition of claim 1, wherein particles of (i) are dispersed in a mixture which comprises (ii).

3. The composition of claim 1 or claim 2, wherein at least a part of (i) is derived from rubber for recycling.

4. The composition of claim 3, wherein at least a part of (i) is derived from rubber of end- of-life tires.

5. The composition of any one of claims 1 to 4, wherein (i) is produced by using one or more devulcanization aids as well as shear energy to devulcanize vulcanized rubber.

6. The composition of any one of claims 1 to 5, wherein (ii) comprises one or more of polypropylene, polyethylene, propylene-ethylene copolymers, polyethylene modified by one or more C4, C6 and / or C8 olefins.

7. The composition of any one of claims 1 to 6, wherein at least a part of (ii) is material from recycled sources.

8. The composition of any one of claims 1 to 7, wherein the composition comprises at least 10 % by weight of (i), based on a total weight of the composition.

9. The composition of any one of claims 1 to 8, wherein the composition comprises at least 20 % by weight of (ii), based on a total weight of the composition.

10. The composition of any one of claims 1 to 9, wherein the composition further comprises paraffinic oil and / or aromatic oil.

11. The composition of any one of claims 1 to 10, wherein the composition further comprises one or more processing aids.

12. The composition of any one of claims 1 to 11, wherein the composition further comprises one or more crosslinking agents for (i).

13. The composition of claim 12, wherein the one or more crosslinking agents for (i) comprise one or more of sulfur, a peroxide, and a resole resin.

14. The composition of any one of claims 1 to 13, wherein the composition further comprises one or more vulcanization accelerators.

15. A thermoplastic vulcanizate composition, wherein the precursor composition of any one of claims 1 to 14 comprises (i) which has been at least partially crosslinked.

16. The composition of claim 15, wherein (i) has been at least partially crosslinked by one or more crosslinking agents.

17. The composition of claim 15 or claim 16, wherein (i) has been at least partially crosslinked by radiation.

18. The composition of claim 17, wherein the radiation comprises one or more of UV, electron beam, gamma and laser radiation.

19. The composition of any one of claims 15 to 18, wherein the composition is present in the form of granules and / or pellets.

20. A molded or extruded article, wherein the article comprises or essentially consists of the composition of any one of claims 15 to 19.

21. A method of producing the composition of claim 15 or claim 16, wherein the method comprises extruding a mixture which comprises (i), (ii) and at least one crosslinking agent for (i) at an elevated temperature which is sufficient to at least partially crosslink (i).

22. A crosslinkable de vulcanized rubber, wherein the devulcanized rubber is produced by using one or more dcvulcanizarion aids as well as shear energy.

23. The devulcanized rubber of claim 22, wherein the one or more devulcanization aids comprise one or more transition metal acetates.

24. The devulcanized rubber of claim 22 or claim 23, wherein at least a part of the shear energy is provided by a twin-screw extruder and / or a two-roll mill.

25. A method of producing the crosslinkable devulcanized rubber of any one of claims 22 to 24, wherein the method comprises contacting vulcanized rubber with a devulcanization aid, followed by subjecting the vulcanized rubber to shear.

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